様式２

SPICA
Mission Requirement Document

本文書は次世代赤外天文衛星 SPICA のミッション要求を規定したものである。
This document defines the mission requirement of SPICA.

次世代赤外天文衛星、SPICA、ミッション要求書
キーワード
Next-generation Infrared Astronomy Satellite, SPICA, MRD
Keyword
■一般

□取扱指定

情報の区分

開示制限解除年月：付
先宇宙科学研究本部

配

配
付
正
種
類
1
部
数
関連

□秘
□部外
開 示 制
限
年
月

□社外
開示制限

承認

点検

．

．

作成

．

．

技術資料番号
RSE-SP08001

．

i

□極秘

．

□特殊
(TSS SSS SS)

改訂符号A

宇宙科学研究本部

改訂記録

符号

年月日
2008.10.31

承認

点検

作成
松原

改訂箇所
全編

改訂内容、理由等
英語による表記をセクションタ
イトル等に付記した

2008. 12. 8

松原

表 2 および 3

English translation added (notyet complete)A

See ``contributors” in the

松原他

Draft

Appendix for authors’ list

01

2009. 08.07

02

2009.08.17

04

2009/08/28

05

2009/09/01

06

2009/09/30

07

2009/10/10

08

2009/11/24

09

2010/01/27

10

2010/01/31

11

2010/05/28

中川

用語の統一、望遠鏡透過率要求・指向精度要求追加A

2010/05/28

01

2010/05/30

02

2010/06/04

03

2010/08/04

Released for SRR
Table2 &3 (as images) are also
included in a single document.
指向精度最新に改訂。
Revised for the consistency
with the SRR concept of`nominal’and`optional’
instruments.
SRR での指摘事項を受けて、2章・3 章を改訂した。

松原

2

目次 Table of Contents
1.

2.

はじめに Introduction ........................................................................................................... 5
1.1.

本書の目的 Purpose of the Document ............................................................................ 5

1.2.

関連文書 Related Documents ......................................................................................... 7

ミッションの目的 Mission Objectives ................................................................................... 8
2.1.

背景および概要 Background and Overview .................................................................. 8

ミッション目的・意義 Mission Objectives and Purposes .................................................. 10「ミッション目標」について Targets of the Mission ......................................................... 12「成功基準(サクセスクライテリア)」について Success Criteria ........................................ 13搭載する科学観測装置について Focal-Plane scientific instruments onboard ................... 15
2.2 Resolution of Birth and Evolution of Galaxies ................................................................. 15
Objective #1: Probing the High-Redshift Universe toward the Epoch of Reionization .... 15
Objective #2: Origin of Cosmic IR Background .................................................................. 20
Objective #3: Metallicity Evolution of Evolving Galaxies Revealed with SPICA ............. 24
Objective #4: Supermassive Black Hole Mass Growth History ......................................... 26
Objective #5: Cosmic Star-Formation & Mass Assembly History ..................................... 29
2.3 Life Cycle of Interstellar Dust .......................................................................................... 32
Objective #1: Study of Dust-forming Supernovae .............................................................. 32
Objective #2: Dust and Molecular Shells around Low- and Intermediate-mass Stars..... 34
Objective #3: Dust formation and grain growth in Dense Molecular Clouds.................... 36
Objective #4: Study of Supernovae Remnants.................................................................... 38
Objective #5: Interstellar Medium in Nearby Galaxies ..................................................... 41
Objective #6: Imaging and Spectroscopic Survey of Galactic Plane .................................. 43
2.4 Studies of Exoplanets and Solar Systems ........................................................................ 47
Objective #1: Direct Detection and Characterization of Exoplanets ................................. 47
Objective #2: Dissipation of Gas from Proto-planetary Disks ........................................... 51
Objective #3:

Debris Disk Surveys ................................................................................... 53

Objective #4: Role of Ice for Planet Formation ................................................................... 55
Objective #5: Survey of Primordial Objects in the Solar System ...................................... 57
3.

ミッション要求 Mission Requirements .............................................................................. 61
3.1 科学目標・成功基準からミッション要求の導出 Mission Requirement Breakdown from
Scientific Targets and Success Cliteria .................................................................................. 61
3.2 ミッション要求サマリ Summary of Mission Requirements ............................................ 63
3.3 ミッション要求の詳細 Overview & Summary of Mission Requirements ........................ 65
3.4 科学目的別特記事項 Special topics for each Scientific Objectives .................................. 743

3.4.1. 銀河の誕生と進化過程の解明 Resolution of Birth and Evolution of Galaxies ......... 74
3.4.2 銀河星間空間における物質輪廻の解明 The Transmigration of Dust in the Universe76
3.4.3 惑星系形成過程の総合理解 Thorough Understanding of Planetary System Formation 76
4.

トレーザビリティ、根拠資料 Traceability Documents....................................................... 79
4.1.

SPICA ミッション要求の提示履歴 Presentation Log to Stake-holders ...................... 79

4.2.

SPICA 関連の政策文書（抜粋）Related Political Documents ..................................... 79

貢献者リストList of Contributors ........................................................................................... 86

4

1. はじめに Introduction
1.1.

本書の目的 Purpose of the Document
本文書は、プロジェクトマネジメント実施要領(システムズエンジニアリング推進室長
通達 19-1 号 2007 年 4 月 27 日)第 2 章第 6 条に従い、次世代赤外天文衛星 SPICA のミッション要求を規定する。
本文書はユーザである天文コミュニティからの要求をもとに次世代赤外天文衛星
SPICA ミッションの目的を明文化したものである。ミッションの目的は科学的目標と技術的意義として具現化され、それらの目標をもとにミッション要求として規定する。また、ミッション終了後に目標の達成度を評価するための成功基準についても明文化する。
図 1.1-1 にミッション要求書の概要図を示す。
本文書で規定したミッション要求は、システム検討のベースラインとなるものである。
開発の進捗やシステムの実現、軌道上での運用結果に対し、確実なミッション達成へと進んでいることを確認するための指標とする。また、関連するステークホルダーの意見・
期待・ニーズや状況の変化によりミッション要求の見直しが必要となった際には、ミッション要求を変更することに伴うミッション達成への影響について検討するための源泉資料として活用される。
This document defines the mission requirement of SPICA, the next generation
infrared space telescope. Based on the motivations and requests from the user, theastronomical communities, this document clarifies the objectives of the SPICA
mission. The objectives of the mission are more concretely expressed by various
scientific targets (plus also technical purposes), and based on these targets, themissionrequirements,

such

as

required

specifications

of

the

missioninstrumentations, scientific operations etc. are defined. Also the success criteria, bywhich the evaluation of the mission achievement will be addressed, are clearly
described. Overview of structure of this document is shown in Fig.1.1-1.
The mission requirements described here will give the baseline of the study of thesystem requirements. In the future, this document will also be used to confirm thedevelopment status, system performance, and operational results on orbit etc. arewell in-line with the mission requirements described in this document. The
description in this document may be updated depending on the change in thestake-holder’s opinions or external conditions, and in such case this document will be
used as the source and reference document to estimate the effects on the mission
achievement.

5ミッション要求書の範囲
Scope of the Mission
Requirement Document

背景・意義
Background & Purposes
SPICA の目的
Objectives
SPICA の目標

成功基準

Targets

Success Criteria

SPICA の ミッション要求
Mission Requirements

SPICA の 各種仕様
Various Specifications

図 1.1-1 ミッション要求書の概要図
Fig,1.1-1 Overview of the structure of Mission Requirement Document

6

1.2.

関連文書 Related Documents①

上位文書 Program Documents
1.

JAXA 長期ビジョン –JAXA2025- (2005 年 8 月 31 日 第 2 版)

2.

宇宙開発に関する長期的な計画(総務大臣・文部科学大臣 2008 年 2 月 22 日)

3.

2010 年代の赤外線天文学(光赤外天文将来計画検討会検討報告書編集委員会 2005 年 3 月 20 日)②

適用文書 Applicable Documents
1.

プロジェクトマネジメント実施要領

第 2 章第 6 条(システムズエンジニアリング推進室長通達 19-1 号 2007 年 4 月 27 日)
2.

SPICA Mission Definition Document(Issue③

1.0 August 21, 2009)

参考文書 Reference Documents
1.

次世代赤外線天文衛星 SPICA ミッション提案書(次世代赤外線天文衛星ワーキンググループ 2007 年 9 月 第 2 版)

2.

SPICA A Cosmic Vision Proposal for a Joint JAXA/ESA Mission to Discover
Origins of Planets and Galaxies (ESA)

3.

第１９期日本学術会議・天文学研究連絡委員会・特別議事録

4.

システムズエンジニアリングの基本的な考え方 初版(2007 年 4 月 B 改訂

BDB-06007B)

7

2. ミッションの目的 Mission Objectives
2.1.

背景および概要 Background and Overview①

学問的背景 Scientific Background
我々の宇宙は約 137 億年前にビッグバンで生まれた。その後の宇宙の進化の歴史の中で、現在の我々の世界を構成している各種の天体が誕生、進化してきたと考えられている。
しかし、それらの天体が「いつ」「どのように」誕生、進化してきのかは、未だによくわ
かっていない。SPICA は、宇宙の歴史における「天体の誕生と進化」という大きな謎に挑む。
The universe began 13.7 billion years ago by “Big-Bang”, and various kind of objects –constituent of our world – were born and have evolved through the history of theuniverse. SPICA’s challenge is to resolve the big question : “when” and “how” suchobjects were born and have evolved.

②「あかり」との関係 Relation to “AKARI” space infrared telescope「天体の誕生と進化」という大きな謎を解明するには、宇宙からの赤外線高感度観測が必要不可欠である。様々な天体が形成される時，その温度が絶対温度で 3K から 300K に対応し，赤外線で観測されるからである。宇宙誕生(ビッグバン)の光といわれる宇宙背景
放射も，その誕生の際は約 4000K であったが，宇宙膨張のため現在は 3K の温度で観測される。
In order to resolve the “big question”, infrared observation with high sensitivity fromspace is mandatory, since the temperature of primordial objects is 3-300K emitting
majority of their energy in the infrared and submillimeter wavelengths.
宇宙からの赤外線観測を進めるべく、JAXA は 2006 年 2 月に赤外線天文衛星「あかり」を打上げた。「あかり」は全天を観測することを目的の一つとした赤外線サーベイ観測衛星である。従来の赤外線サーベイ観測衛星である IRAS(Infrared Astronomical Satellite・
NASA・1983 年打上げ) と比較すると、解像度が画期的に向上しており、「あかり」はい
わば究極の赤外線サーベイ観測衛星として成果を挙げ、多くの若い星・原始惑星系円盤や赤外線銀河を発見した。
JAXA launched AKARI infrared astronomy satellite in Feb. 2006. AKARI’s major
objective is the advanced all-sky survey in the infrared, with much better spatial
resolution than that of IRAS launched by NASA in 1983. AKARI is a suprime infrared
surveyor discovered many young, stars, debri disks, and infrared galaxies.
しかしながら「あかり」はサーベイ観測衛星としては優れた空間分解能をもっているものの、高い波長分解能・空間分解能をもとに詳細な観測を行う天文台型の観測衛星と比較すると空間分解能が不足していることは否めない。「あかり」の最も長波長における空間分解能は 50” と人間の視力程度であった。
However, AKARI was not an space observatory. Even though it has excellent spatial
8

resolving power as an all-sky surveyor (50” in the far-infrared), it is not enough to
explore the detailed nature of the objects for which a space observatory,

which

enables us to observe objects with long exposure time and better spectral and spatial
resolution, is necessary.
「あかり」のサーベイ観測の結果を活かし、さらなる謎の解明のためには、より優れた
空間分解能と感度をもった次世代の天文台型の観測衛星が必要であり、大口径の宇宙望遠鏡が切望されている。
Therefore, the next generation space infrared telescope with a large collecting
aperture, superior spatial resolution and the sensitivity, is strongly requested③

国際的位置付け Standpoint in the International Trend「天体の誕生と進化」という大きな謎の解明には、赤外線、特に中間・遠赤外線での高感度の観測を行なうことが必要になる。2010 年代までに計画されている赤外線ミッショ
ンは、近赤外線(JWST：James Webb Space Telescope・NASA/ESA・2014 年打上げ予定)
やサブミリ波(Herschel：ESA・2009 年 6 月打上げ) に集中したものであり、中間・遠赤
外線での高感度観測ミッションは、国際的に見ても SPICA の他に存在していない。
Hershel, aiming to observe mainly submillimeter wavelength beyond 60μm, waslaunched in June 2009. In this decade only JWST (James Webb Space Telescope,
NASA/ESA) is planned to be launched (currently in 2014), which, however, aims toobserve mainly near-infrared upto 5μm. Even from the viewpoint in the international
trend, only SPICA is aimed to observe mainly mid and far-infrared wavelength withhigh sensitivity.

9ミッション目的・意義 Mission Objectives and Purposes
SPICA は「我々はなぜ、かく在るのか？」という人類の基本的問いの中で特に「銀河誕生のドラマ」および「惑星系のレシピ」を探る次世代赤外線天文衛星である。この宇宙の歴史における「天体の誕生と進化」という大きな謎に挑むため、銀河の誕生と進化、星と惑星系の誕
生と進化、物質の進化の研究を行う。中でも、赤外線による観測によって大きな進展が期待される「銀河誕生のドラマ（銀河の誕生と進化過程の解明）」と「惑星系のレシピ（惑星系形成
過程の総合理解）」そしてこれらすべての基礎として「銀河星間空間における物質輪廻の解明」
を科学的目的として掲げる。これらの相互関係を図 2.1-1 に示す。
Among the basic questions of human beings “who are we? Where are we from?” SPICA
will investigate “the drama of galaxy formation” and “the recipe for planetary systems”. In
order to challenge this big question in the history of universe, we present three major
science objectives: “resolution of birth and evolution of the galaxies”, “thoroughunderstanding of planetary system formation”, and “the transmigration of dust in theuniverse” as the basis of the former two objectives, with SPICA. In Figure 2.1-1, therelationship of these science objectives is shown.

図 2.1-1 SPICA ミッションの３大科学目的相互の関係。
Figure 2.1-1 Relationship among the three major science objectives performed with SPICA.
これらの科学的目的について、特に赤方偏移した宇宙初期の放射と低温物質からの放射に感度の高いスペースからの赤外線の観測によって、大きな科学的進展が期待される。次節から、
10

具体的に詳しく述べる。
また、科学的意義ばかりでなく、SPICA ミッションには、以下のように重要な技術的意義が存在する：
大型軽量ミラー技術の開拓：「あかり」や Herschel で培われた SiC 冷却軽量鏡技術を発展させ、大口径単一鏡の製作技術・その光学性能の低温での実証技術を開拓する。2009 年に実現された Hershel 宇宙望遠鏡は、遠赤外線〜サブミリ波といった長波長での使用に耐える鏡面精度に過ぎず、しかも温度は 70K であった。
赤外線観測機器技術の開拓：極低温に冷却された望遠鏡によってこれまでになく高感度の赤外線観測を実現するためには、それに見合う高感度・大画素数の赤外線検出器がぜひとも必要である。
効率的冷却システムの開拓：従来の赤外線衛星の概念を打ち破り SPICA は、地上では冷却せずスペースに到達してから望遠鏡・観測装置を冷却する。これを実現するための断熱/放熱技術、
機械式冷凍機の独自開発を行い、今後も我が国の資産というべき「効率的冷却システム」の確立を目指す。
ラグランジュ点利用技術の開拓：JAXA 長期ビジョンに掲げる「深宇宙港」という目標の実現の第一歩として、我が国が初めてラグランジュ点を利用した科学観測を実現する意義は大きい。
また他のスペースからの天文学ミッションにおいても L2 点は非常に魅力的である。
Besides the scientific objectives, there are also important mission objectives on thetechnology in space mission:
Light-weight, large mirror technology for space mission: based on the heritage of SiC
low-temperature, light-weight mirror technology for AKARI and Hershel, we will
undertake the establishment of fabrication and low-temperature performance evaluation
for large, monolithic, light-weight mirror. The large-mirror onboard Hershel achieved
surface accuracy which is only capable to use at far-infrared and submillimeter
wavelengths and the mirror is 70K.
Development of advanced instrumentation for space infrared observations: to achieve theextremely high sensitivity with cooled telescope, large-format infrared array detectors
with high-sensitivity are mandatory.
Effective cooling technology in space: unlike the past infrared telescopes in space, thetelescope and the instruments of SPICA will be cooled when the spacecraft will be put
into space.
Technology Application at Sun-Earth Lagrangian point: as the first step toward the“deep-space port”, one of the targets in the JAXA’s long-term Vision, scientificobservations with SPICA in L2 point will be the 1st space technology application among
the Japanese space activities. The L2 point is also very promising place for other spaceastronomy missions.

11

SPICA の科学的目的を表 2 にまとめる。
「目的」はミッションの内容に重点を置いた記述としている。そのため「目標」に比べて抽象的であり、長期的視点に立った記述である。
In Table 2, scientifc objectives of SPICA are summarized. “Objectives” are describedsomewhat abstractly than “Targets”, since they express more emphasis on the purpose of
the mission in the long-term vision in science and space technologies.
「ミッション目標」について Targets of the Mission「目標」は「目的」をもとに具体化された、目指す成果・数値・数量・時間などに重点を置いた記述としている。そのため、目的を達成するための観測方法やそれによって得られる成果について記述している。
SPICA’s targets are shown in Table 2. “Targets” are concrete description of aimed results,
quantitative numbers, or observing duration, etc., based on the “Objectives”. Thus
observing methods as well as expected results are also described.
SPICA ミッションの目標（科学および技術）を以下にまとめる：
科学的目標


銀河誕生のドラマを探る
宇宙の進化の歴史を示す宇宙赤外線背景放射が、どのような天体から構成されているかを明らかにする。
宇宙の歴史の大半(宇宙年齢の 90%以上）の期間における、銀河・星形成史を明らかにする。



物質輪廻の解明

銀河星間空間における物質循環、特にダストの形成と進化過程を明らかにする。


惑星系のレシピを探る

惑星系の形成過程を総合的に明らかにする。
太陽系内における小天体・固体物質分布の観測から、太陽系形成の歴史を探る。
技術的目標


日本の戦略宇宙技術の開拓

我が国で初めてラグランジュ点の利用技術を確立する
今までの冷却システムに比べて、重量効率をはるかに向上させた冷却システムを実証する。
また SPICA を用いて研究活動を推進する天文科学コミュニティが掲げる科学的目標を表 2に示した。この１６項目（上記の衛星ミッション目標も含まれている）には、現時点でのオプ
ション機器・機能が使用されるもの含まれている。システム定義審査までには、コスト及び技
術的実現性と科学的価値のトレードオフ検討を進め、その結果、搭載することに決定した装置
及び機能のみを使用する前提で再整理する。その上で、これらすべてを達成することを目指して、観測運用計画を立案する。
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「成功基準(サクセスクライテリア)」について Success Criteria「成功基準」は「目標」の達成度の度合を判断するための評価基準である。
「成功基準」は、
JAXA が国民に対して宣言するものであり、JAXA における経営審査を経て宇宙開発委員会における推進部会にて審査されるものである。(NC 版時点では、宇宙開発委員会における審査未了)
なお、成功基準は達成度を明確に判断できるよう簡潔な表現としているため、目標とセットで確認する必要がある。
The “Success Criteria”, also presented in Table 2, are criteria for evaluating theachievement of the “Targets” of the mission. The “success criteria” are also a JAXA’s
declaration to the people in Japan: they are reviewed at the JAXA headquarter first andthen reviewed by the Space Advisory Committee of the Japanese government. Note thatthe success criteria are just written concisely in order to judge the mission achievement
clearly: thus the corresponding targets should be simultaneously referred.
「フルサクセス」はプロジェクトが各種リソースや制約を考慮した上で達成すべき事項を記述している。SPICA では、キーサイエンスとして独創的かつ先端的な成功を達成するための基準を定めている。成果の規模としては【中】以上のサイエンスとして定義する。
“Full success” level should be achieved by the project within the available resources andconstraints. In SPICA project, this is the standard for the successful achievement of uniqueand advanced key sciences. The size of results is defined as [moderate] impact on thecorresponding scientific topics.
「エクストラサクセス」はパラダイムを変えるような大きな成果を達成するための基準を定めている。成果の規模としては【大】のサイエンスと定義する。なお、設計寿命を超えた観測により得られる成果あるいは不定性などの運・不運に左右される事項については、それらの条件を記述する。
“Extra Success” is a criterion to judge if the results of the mission is huge impact, evenchanging the paradigm. The size of results is defined as [large] impact on thecorresponding science. In addition, if the results are obtained from observations beyond thedesigned mission life, the condition of them shall be defined.
「ミニマムサクセス」は投じた費用に対する最低限の科学的成果が得られる基準を示す。
SPICA では、前節に掲げたフルサクセス成功基準のうち 2 つ以上達成することとする。
“Minimum Success” is a criterion to judge if the mission achieved the minimum scientificgoals in exchange for the paid cost. In case of SPICA, among the above criteria, “Minimum
Success” is defined to achieve at least two [moderate] impact scientific goals.
表 2.1-2 に SPICA ミッションの成功基準をまとめる。

13

表 2.1-2 SPICA ミッションの成功基準
Table 2.1-2 Success Criteria of SPICA mission

14

また、SPICA を用いて研究活動を行う天文科学コミュニティが掲げるフルサクセス・エク
ストラサクセス成功基準も表 2 に示した。これらは科学目標同様、現時点でオプションの装置・機能を使用するものを含んでおり、システム定義審査までに搭載することに決定した装置及び機能のみを使用する前提で再整理する。
搭載する科学観測装置について Focal-Plane scientific instruments onboard
焦点面観測装置として以下を想定する（実際の搭載に向けたプロセスについては別文書に記載される）：
中間赤外線撮像装置(MIRACLE)
中間赤外線中分散分光装置(MIRMES)
中間赤外線高分散分光装置(MIRHES)
遠赤外線分光撮像装置(SAFARI)
焦点面ガイドカメラ(FPC-G)
近赤外線カメラ(FPC-S)
中間赤外線コロナグラフ(SCI)
遠赤外サブミリ波分光装置(米国主導装置：BLISS 等。以下 BLISS で代表する)
このうち、MIRACLE の短波長（5-20μm）低分散分光機能、MIRMES の短波長（10-20μm）中分散分光機能、MIRHES、FPC-S、SCI、米国主導装置はオプションである。ただし FPC-S は FPC-Gのバックアップ機能を有する必要があり、オプションとするのは科学観測機能のみについでである。
これらのより詳しい仕様については、Mission Definition Document (MDD) [AD-2]に記載されている。
Currently considered Focal Plane-instruments (FPIs) onboard SPICA are as follows:
MIRACLE (Mid-InfRAred Camera w/o Lens)
MIRMES (Mid-IR medium-resolution echelle spectrometer)
MIRHES (Mid-IR high-resolution echelle spectrometer)
SCI (SPICA Coronagraph Instrument)
SAFARI (SPICA Far-infrared Instrument)
Far-IR & Submillimeter spectrometer (US-lead instrument, such as BLISS :Background-Limited Infrared-Submillimeter Spectrograph)
FPC (Focal-plane finding camera) #FPC-G is a guider camera for the attitude control.
For their detailed specifications, see Mission Definition Document (MDD) [AD-2].
2.2 Resolution of Birth and Evolution of Galaxies
Objective #1: Probing the High-Redshift Universe toward the Epoch of Reionization
We will identify and characterize dust-obscured (i.e., IR-luminous) galaxies at 4<z<10, a
redshift range hitherto unexplored by far-IR/submm observations, and investigate
whether such a population of galaxies played an important role in the early Universe.
15Observational cosmology is now on the verge of making another great breakthrough in the historyof science: to identify the first generation of galaxies that appeared and reionized the intergalactic
space, thereby ending the so-called “Dark Ages” of the Universe.

This process, called “cosmic

reionization”, marks a major phase transition of the Universe, after which the intergalactic space
has become transparent to HI ionizing radiation.

Recent WMAP observations indicate that cosmic

reionization took place around z~10 (e.g., Dunkley et al. 2009) while QSO absorption-line studies
suggest that the reionization process is not complete to z~6 (e.g., Fan et al. 2006). Thus, afundamental question is “When and How the Universe experienced the re-ionization epoch ? Did the first
dust already emerge during the re-ionization era and absorb ionizing photons?” Our challenge, therefore, isto understand how galaxies formed and evolved during this critical epoch in the history of the
Universe.
Deep optical and near-/mid-infrared observations are
now routinely detecting galaxies up to a redshift of 7(and even beyond photometrically), providing a firstglimpse of galaxy populations near the epoch ofreionization.

Preliminary results suggest that therest-frame UV luminosity density (and therefore theUV-derived star formation rate density (SFRD)) is
Fig.2.2-1: Evolution of the UV
luminosity density (right axis) and thecorresponding UV-derived starformation rate density (left axis)
integrated down to 0.2 L*z=3 in eachredshift bin (Bouwens et al. 2008).

sharply declining from z~3-4 to z~10 (Bouwens et al.
2008; Fig.2.2-1).

The next question is whether thisobserved sharp decline reflects the true history ofcosmic star formation or it is substantially steepenedby the effect of dust extinction. For example, whenz~3-4 Lyman Break Galaxies (LBGs) were firststudied, a similar decline was seen at z~3-4, but it

was later understood as the effect of dust extinction.

In fact, when corrected for dust extinction,

the UV-derived SFRD stays nearly flat at z~1-4 (e.g., Steidel et al. 1999).

Furthermore, evenheavier dust extinction could make galaxies drop out of optical (i.e., rest-frame UV) surveys all
together (e.g., LBG surveys), and indeed such a population of luminous but heavily dust-obscured
galaxies have been discovered by submillimeter observations (e.g., Smail et al. 2002).

This leads toa question we hope to answer with SPICA: “Did dust-obscured (i.e., IR-luminous) galaxies play animportant role in the early history of the Universe at 4<z<10?”

Such a population could certainly

hide a substantial amount of star-forming activities at z>4 from optical/near-IR observations
although its relevance to cosmic reionization would need to be examined due to the difficulty of
dust-obscured galaxies to release intergalactic HI ionizing radiation efficiently. However, the dust
emission as a high-z probe provides us with unique opportunity to identify the major epoch of heavy
16element production.
SPICA will play a major role in investigating high-z sources (1) to identify 4<z<10 IR-luminous
galaxies and high-z quasars, and (2) to characterize individual detected sources.

For (2), we expect

a number of interesting targets to be known beforehand from various JWST/ALMA deep surveys aswell as from the SPICA surveys mentioned below.

We will also mention the great potential offeredby lensing cluster surveys (3).
(1) Identify 4<z<10 IR-luminous galaxies
SAFARI Spectro-imaging survey of 7.7 μm PAH emitters: The 7.7 μm PAH featureis the mostluminous and conspicuous emission feature seen in the rest-frame mid-IR spectra of star-forming
galaxies.

For example, the 7.7 μm PAH features of z~2 star-forming submillimeter galaxies(SMGs) have luminosities of ~1010 L (Pope et al. 2008; Fig.2.2-2).

With a flux sensitivity of 10-19

Wm-2 in the low-resolution (R~20) FTS mode, SAFARI can conduct an efficient survey of suchstrong 7.7 μm PAH emitters up to z~10.
MIRACLE Narrow-band imaging/multi-slit survey of Hα emitters: Hα is the brightest hydrogen
recombination line, and therefore will serve as a good marker for high-redshift galaxies. Hα will beredshifted into the MIRACLE passband at z~7 (5.25 μm).

With specifically designed narrow-band

filters/slitmaks together with the large FOV, MIRACLE can conduct an efficient survey of Hαemitters at z>7.

Note that such a Hα survey will detect not only dusty IR-luminous galaxies but

also UV-bright galaxies with minimal dust extinction and strong line-emitters such as giant
Lyα blobs.
MIRACLE and FPC-S spectroscopy of high-z quasars: through future NIR imaging surveys fromthe ground or from the space, it is expected that many quasars will be discovered at z > 6 by thelaunch of SPICA. One of the important issues of high redshift quasars study is how rapidly quasars
are growing at high redshift, as many different models are proposed to explain the existence of ~109
M⊙ black holes at z ~ 6 when the universe was less than 1 Gyr old. AKARI NIR grism spectroscopy
has provided a glimpse of the supermassive black hole (SMBH) growth at z ~ 6, showing that theluminous quasars are shining near at the Eddington luminosity, unlike the lower redshiftcounterparts. The AKARI result suggests that SMBHs seem to be in rigorous growth phase at z > 6
with the SMBHs with 1010 M⊙ appearing only at z < 6 (Im et al. 2010 in preparation; Im 2009 at
AKARI conference). SPICA’s MIR and FIR coverage will detect the IR fluxes of high redshiftquasars, allowing us to estimate the Eddington ratio – a crucial piece of information for estimating
the accretion rate – of high redshift quasars. The MIRACLE spectroscopy, together with FPC-S’s
LVF spectroscopy, will provide us with the Balmer line measured BH masses as well as metal line
information in the optical wavelengths which are important to trace the metal enrichment historyof the broad line region around SMBH in the early universe. A 5-year blind parallel imaging survey
in NIR with three broadband filters to ~26-27 AB magnitude limit has a potential to uncover dozens
of quasars at z > 6 over more than 50 square degree area which will be difficult to find from the17

ground-based surveys or even with JWST.
(2) Characterize individual detected sources
BLISS Fine-structure/H2 line spectroscopy: Some low-redshift (z~0.2) luminous galaxies (e.g.,brightest cluster galaxies in strongly cooling cluster cores) show very strong fine-structure (e.g., [NeII] 12.8 μm) and H2 lines with luminosities up to ~109 L (Egami et al. 2006; Fig.2.2-2). With a flux
sensitivity of 10-20 Wm-2 in the medium-resolution (R~700) mode, SPICA/BLISS can detect suchstrong lines up to z~10, providing information on the physical properties of ionized gas components
as well as of H2-emitting regions.

Compared to these narrow emission lines, the broad PAHfeatures will be much easier to detect, and the strength of the 7.7 μm PAH feature, for example,
may be used to estimate the metallicity.
MIRACLE rest-frame optical spectroscopy: MIRACLE should perform rest-frame optical
spectroscopy of high-redshift galaxies in order to diagnose their nature by using the line ratio,
although JWST has a similar capability.

Fig.2.2-2: (Left) Strong 7.7 μm PAH feature detected in z~2 SMGs (Pope et al. 2008); (Right) Strong[Ne II] 12.8 μm fine-structure line as well as abnormally luminous H2 lines detected in the brightest
cluster galaxy in Zwicky 3146, an X-ray-luminous galaxy cluster in which the existence of a cluster
cooling flow is suspected (Egami et al. 2006).
FPC-S follow-up of GRBs: Gamma-ray bursts (GRBs) are the most energetic events in the universe.
Their extreme brightness makes it possible to detect them at very high redshift, and GRB afterglow
has been identified out to z=8.3 (Tanvir et al. 2009; Im et al. 2009), which marks the highest,
spectroscopically confirmed redshift of any astronomical object. Their extreme brightness in theinitial phase allows us to use them as a probe of the intergalactic medium at the epoch of
re-ionization. We expect current and future GRB missions continue to provide prompt alert andlocalization of GRBs which are candidates for being at the highest redshifts (6 < z < 15). Althoughthese GRBs at the reionization epoch will be studied with JWST, a rapid target of opportunity
observations with FPC-S, especially with LVF low resolution spectroscopy mode, will enable us to18

identify the exact location of the redshifted Lyman break and going deep to identify trace of a small
fraction of ionized Hydrogen in IGM. Subsequent follow-up observation with MIRACLE or SAFARI
will provide an exciting opportunity to understand the GRB infrared emission which is poorly
understood. The GRBs will be the brightest sources at the reionization epoch, therefore rapid GRB
follow-up observations through SPICA will provide a unique opportunity to examine the highredshift universe. To make this observation possible, FPC-S and another science instrument shouldbe operated in parallel so that one can execute a rapid switching from one instrument to another.
(3) Lensing cluster surveys
By observing the fields of massive lensing clusters and thereby taking advantage of their great
gravitational lensing power, we can increase the sensitivities by up to a factor of 20-30.
This great gain in sensitivity is especially important if we consider the possibility thathigher-redshift galaxies may be systematically less massive (and therefore less luminous) as
predicted by hierarchical structure formation theories.

Note that both SAFARI and MIRACLE

have FOVs that are large enough to contain the strongly lensed cluster-core region (radius~1’).
SPICA’s power: Despite its greatly improved far-IR/submm sensitivities, Herschel is unlikely to beable to probe the Universe at z>3-4 because of its confusion limit. Having the same telescope size,
SPICA is also bounded by the same limit, but its excellent spectroscopic capabilities (e.g., SAFARI,BLISS) will make it possible to detect sources deeper into the confusion by exploiting spectroscopic
information.

In fact, such spectroscopic capabilities are essential for SPICA to penetrate theconfusion limit and fully utilize the excellent sensitivities afforded by the cold telescope.
ALMA, together with JWST, is likely to detect and identify dust-obscured (i.e., IR-luminous)
galaxies well beyond a redshift of 4 and toward z~10.

However, the rest-frame mid-IR spectral

range, which only SPICA can probe, will be crucial to understand the properties of detected sources(e.g., AGN vs. Star formation through the PAH feature strength).

Also, SPICA will offer

significantly faster mapping capabilities with respect to ALMA and JWST, and this may become an
important factor when we search for rare high-redshift galaxies.

19

Objective #2: Origin of Cosmic IR BackgroundWe will resolve the cosmic far-infrared background light into individual objects, andreveal the origin of the cosmic far-infrared background residual brightness andfluctuations.
Since the Cosmic Infrared Background (CIB) has been found with the COBE satellite (Puget etal. 1996; Hauser et al. 1998), it has been known that a large fraction of the radiation energy in the
Universe is released in the far-infrared wavelength. Main source of the far-infrared background has
been thought to be the re-emissions of UV light absorbed by dust in the star-forming galaxies athigh redshifts. Up to now, many efforts have been made to resolve the CIB into individual galaxies
by deep surveys with infrared space telescope such as ISO, Spitzer and AKARI. However, only
10-30% of the CIB can resolve to each galaxies, and main bulk of the CIB is still unknown well.

AKARI
COBE
IRAS

Spitzer Stacking

Model CIB
(Lagache et al.)Spitzer &Galaxy counts

Fig.2.2-3 The absolute brightness of the CIB measured by AKARI,
compared with the integrated flux of resolving galaxies.
By using the ultimate sensitivity and high resolution of SPICA, we will be able to resolve the
CIB into individual objects, and reveal the origin of the cosmic far-infrared background brightness
and fluctuations. The scientific objectives of this program are as follows.
1). Source counts for infrared galaxies
Because SPICA has a large 3-m class cold(<6K) telescope, its sensitivity is at least 2 orders of20

magnitude better than that of Herschel, and its spectral resolution is at least 3 times greater thanthat of AKARI and Spitzer. With an ideal sensitivity for point sources, SPICA has a capability toresolve 90% and 60% of the CIB at 70μm and 160μm, respectively (Dole et al. 2004). Galaxy number
counts are useful to constrain the evolutionary scenario of galaxies. AKARI results indicate thenecessity of the multi-band galaxy number counts, especially around the 100μm (Shirahata et al.
2009). Furthermore, with low-resolution spectro-imaging capability of SAFARI, we may able toresolve sources below the turn-over flux density (~1mJy at 70μm) and obtain their low-resolution
SEDs at 35-210μm from which we can infer their crude redshifts.
2). Examination of the properties of detected individual galaxies
In order to reveal what kinds of galaxy are dominant in the CIB, the measurements of SEDs ofdetected sources are very important. AKARI extra-galactic deep survey discovered the very young
pure-starburst ULIRGs (Takagi et al. 2009) and the extremely red objects which have the evidenceof co-evolution of both the obscured AGN and starburst (Matsuhara et al. 2009). We can detectstatistically significant number of these galaxies beyond z~3 with SAFARI and MIRACLE
multi-band imaging. Moreover, we have a possibility to detect the dust-obscured (i.e., IR-luminous)
galaxies at 4<z<10, which are the key objects to probe the high-redshift universe toward the epochof reionization.
3). Stacking analysis with mid-infrared and sub-mm wavelength
The stacking analysis with other wavelength is a useful method to investigate the properties ofunresolved sources. Because the galaxy confusion limit at the mid-infrared wavelength is much
lower than that at far-infrared wavelength, the stacking analysis for the mid-infrared wavelength
have enough possibility to escape from the galaxy confusion limit. On the other hand, because thecosmic sub-mm background are almost completely explained by distant sub-mm galaxies, thestacking analysis for the sub-mm galaxies can prove the distant universe.
4). Absolute brightness and spatial fluctuations of CIB
As the results of AKAFI far-infrared deep survey, we obtained new limits on the absolute brightnessof CIB, and found the signature of the galaxy clustering at angular scales of 10-30 arcmin(Matsuura et al. 2009). With the aim to detect the sign from the 1st stars at the re-ionization epochof the universe, we will study the far-infrared background fluctuations in an effort to reveal their
origin through detailed analyses such as SED fitting to multi-wavelength images.
We propose a multi-wavelength far-infrared deep survey with making use of the very uniquecapability of the SAFARI on SPICA, to obtain statistically significant number of source samples andto detect clearly the CIB fluctuation with the angular distance up to degree-scale. In order to21measure the SEDs of detected galaxies and the absolute brightness of CIB, low-resolution
spectro-photometric imaging mode (Δσ~10 cm-1) will be very useful. The required detection limit is~300μJy (5-σ). To avoid the galactic cirrus contamination, a low HI-column density region should beselected for the survey area. The follow-up observations with MIRACLE imaging with band filters
are also necessary.

Fig.2.2-4a Predicted performance of SAFARI and MIRACLE with SED templateof ULIRG at various redshifts.
In order to measure the absolute brightness of the CIB, we should cool not only the telescope but
also the baffle, as possible as we can. We also need the cold shutter and the calibration lamps.
5) Near-IR CIB observation with FPC-S
Light of first stars could be observed as background radiation in the near-IR. COBE/DIRBE and
IRTS/NIRS have tried to detect this and an excess emission background was detected.
AKARI recently observed fluctuation of the sky towards NEP and clearly detected a large scale
structure (Fig.2.2-4b). The fluctuating component at large angles has a blue stellar spectrum, whichcannot be explained by the clustering of faint galaxies. A typical angular scale of the structure, 200
arcsec, corresponds to ~10 Mpc at present, that is a typical distance between cluster of galaxies.
These results could be a piece of evidence on the structure formation at pop.III era.

22Fig.2.2-9 Smoothed image of NEP field observed with AKARI. Angular diameter is 10 arc-minutes.
Wavelength band is 2.4, 3.2 and 4.1 μm, from left to right.
FPC has a unique capability of surface spectroscopy at 0.8 ~ 5 μm with a combination of linear
variable filter and step scan of the sky. Measurement of the spectrum of the sky with low spectral
resolution certainly provides important data to investigate pop.III era.

Larger field of view andmuch bigger throughput of FPC/SPICA than those of JWST makes it possible to achieve uniqueobservations on CIB.
a) Spectrum of cosmic near-infrared background
FPC is powerful to measure the spectrum of the sky. Observations at several points on the sky
makes it possible to obtain the model and template of the spectrum of zodiacal light. By subtracting
zodiacal light and diffuse galactic light, spectrum of excess emission will be obtained even at the
shorter wavelength side. Thanks to high sensitivity of FPC/SPICA, removal of foreground sources,
faint stars and galaxies, can be executed much better than previous observations. If excess emissionis due to pop.III stars, spectral peak at around ~1 μm should appear. In this case, the peak indicatesthe redshifted Lymann a at the end of pop.III star formation. Peak position and spectral shapeprovide important clue to study the star formation history of pop.III era.
b) Fluctuation measurement
Measurement of fluctuation of sky also provides important result. Compared with AKARI andSpitzer, detection limit and angular resolution are much better, and which faint sources down to~27 mag. can be removed. This makes it possible to detect fluctuating power at ~10 arcsec, since
shot noise due to faint galaxies is much lower than AKARI and Spitzer. Furthermore, thefluctuation map can be obtained for the wide wavelength range from 0.8 ~ 5 μm. Absolute
fluctuating power and angular dependence of fluctuation, and their dependence of the wavelength
are crucial pieces of evidence to study the structure evolution at pop.III era.

23

Objective #3: Metallicity Evolution of Evolving Galaxies Revealed with SPICA
We will explore the metallicity of high-z dusty galaxies, which are in the evolving phase in
the galaxy evolutionary processes. We will use FIR emission lines that enable us to study
the metallicity in dust-enshrouded parts in galaxies.
The unprecedented spectroscopic sensitivity of SPICA in mid and far-infrared will enable us to
substantially improve our understanding of the dust-obscured star-formation and AGN growth ingalaxies. This is because in the mid- and far-infrared regions there are plenty of diagnostic lines totrace the star formation and the gas accretion to the super-massive black holes. The diagnostics
lines are atomic/ionic fine structure lines (Spinoglio, Malkan 1992), molecular lines such as H2,
UV-excited emission bands of Polycyclic Aromatic Hydrocarbon molecules (PAHs), and the silicate
features. The spectrometer onboard Herschel can detect the brightest objects at z~1, while SPICA
will be able to carry out spectroscopic surveys out to z~3. Here we focus on the metallicity
measurement of dusty galaxies, one of unique capabilities of SPICA, in the following.
Measuring the metallicity of galaxies at various redshifts is a powerful way to give constraints on
the galaxy evolutionary scenarios, since the chemical properties of galaxies are the result of theirpast cumlative star-formation. Especially the tight mass-metallicity relation of galaxies (i.e., more
massive galaxies have higher metallicity; hereafter MZR) is important, because the MZR suggests
more efficient loss of created metals thgough galactic superwind phenomena in less-massive
galaxies (e.g., Tremonti et al. 2004). A more interesting issue is the redshift evolution of the MZR.
Maiolino et al. (2008) reported a mass-dependent evolution of the MZR between 0<z<3; i.e.,
less-massive galaxies tend to shows gradual metallicity evolution in this redshift range while
massive galaxies completed their metallicity evolution at earlier cosmic epoch (see also, e.g.,
Savaglio et al. 2005, Erb et al. 2006). This may corresponds to the chemical version of the“down-sizing” galaxy evolution.
However, all of the above studies are for “already-evolved” galaxies; i.e., dust-unreddened
populations. Recently it is pointed out that ULIRGs are significantly deviated from the standard
MZR (Rupke et al. 2008, Caputi et al. 2008). Since the ULIRGs are in a rapidly evolving phase,
MZRs (and its redshift evolution) for ULIRGs will give strong constraints on the galaxy
evolutionary scenarios. Such studies are evidently important especially at high redshifts, where alarge fraction of star formation occurred in ULIRGs (e.g., Le Floc’h et al. 2005). Note that thecurrent metallicity measurements for ULIRGs are still relying on rest-frame optical emission lines,
and thus the dust-enshrouded parts in ULIRGs have not yet examined.
A breakthrough in this issue will be achieved through MIR metallicity diagnostics for high-z dusty
star-forming galaxies with using SPICA/SAFARI. Among various potential metallicity diagnostics,
emission-line flux ratios using [NIII]57.2μm are promising. Specifically, the flux ratio of[OIII]51.8μm /[NIII]57.2μm is very sensitive to the gas metallicity. The simultaneous use of24

[OIII]88.3μm in addition to [OIII]51.8μm and [NIII]57.2μm is even better since the density
dependence of the diagnostic ratio is well corrected. This method has an advantage with respect toother NIR-MIR metallicity diagnostics using hydrogen lines (e.g., Verma et al. 2003), since the IRhydrogen lines such as Pfunt and Humphreys series lines are generally very weak. The method
using [OIII] and [NIII] lines has been already applied to the ISO data to infer the metallicity of
Galactic planetary nebulae (e.g., Liu et al. 2001). The superb sensitivety of SPICA/SAFARI enables
us to extend such an approach toward the extragalactic universe. We already confirmed that theflux ratio of [OIII]51.8μm +88.3μm /[NIII]57.2μm works very well as a metallicity diagnostic tool
also for star-forming galaxies, based on detail photoionization model calculations (Nagao, Maiolino,
et al., in prep.). Note that these three lines are the strongest emission from HII regions in galaxies(i.e., excluding PDR lines such as [OI] and [CII], because they comes from different regions).
Here we mention on the detection feasibility. The [NIII]57.2μm line (faintest one among the threelines) from galaxies whose SFR is similar to M82 (Colbert et al. 1999) can be detected up to z~0.4
with SPICA/SAFARI (5 sigma detection with a 1 hour exposure). However, since ULIRGs (that are
our main targets) have ~2 order higher SFRs than M82, we will detect [NIII]57.2μm (and two [OII]
lines simultaneously) from ULIRGs at up to z~2. This redshift range is limited by both flux
sensitivity and the wavelength coverage of SAFARI. Note that a wavelength resolution of ~1000 is
adequate for this science, taking a typical emission-line velocity width of star-forming galaxies to be~300 km/s into account.
Summarizingly,

SPICA/SAFARI

canmeasurethemetallicityof

ULIRGsbasedonreddening-insensitive MIR lines of the [OIII] and [NIII] transitions, up to z~2. This is crucial toexamine the redshift evolution of the MZR for rapidly-evolving galaxies, that will then contribute togive strong constraints on the galaxy evolutionary scenarios.

Fig.2.2-5 Flux of redshifted [OIII] and[NIII] lines (green and red curves),
assuming the M82 spectrum (Colbert etal.

1999).

SPICA/SAFARI

1

hour

sensitivity limit is shown by blue lines.
Note that our main targets are not
M82-like galaxies but ULIRGs, whose
SFR reaches ~100 times higher thanthat of M82.

25

Objective #4: Supermassive Black Hole Mass Growth History
In order to understand the role of supper-massive black holes (SMBHs) in galaxy
evolution, we will make a systematic survey for actively mass-accreting, but elusive,
SMBHs deeply buried in dust in the early universe at z>1, when both star-formation and
SMBH mass growth history have peaks.
The recent discovery that (1) all spheroid galaxies (bulges and elliptical galaxies) ubiquitously
contain super-massive black holes (SMBH) at their centers, and that (2) the masses of spheroid
stars and SMBHs are tightly correlated, strongly suggests that star-formation in galaxies (several
kpc scale) and SMBH mass growth (<pc scale, the so-called AGN activity) are closely linked.
Understanding this co-evolution of galaxies and SMBHs throughout the history of the universe is
one of the most important topics in present astronomy.
The cosmic energy radiation density, which is the sum of star-formation and AGN activity in theuniverse, is even higher in the infrared than in the UV/optical. Hence, more than half of activity inthe universe is hidden behind dust. At z > 1, the population of ultraluminous infrared galaxies(ULIRGs; L(IR) > 1012 L◎) dominates the cosmic infrared radiation, so that distinguishing thedust-obscured hidden energy sources of the ULIRG population is directly related to clarify thehistory of star-formation and SMBH mass growth, and the interplay between galaxies and AGNs, inthe early universe.
Unlike AGNs surrounded by torus-shaped dusty medium, which are classified optically as Seyferts,
the putative AGNs in ULIRG’s nuclei are deeply buried (=obscured along virtually all directions),
and so are very difficult to find. Infrared 3-35 μm low-resolution (R~100) spectroscopy is an effectivemeans to investigate such optically-elusive buried AGNs in ULIRG’s nuclei. First, the effects of dust
extinction are small. Second, we can distinguish between star-formation and buried AGNs, based on
infrared spectral shapes (Fig.2.2-6).
Using the Subaru 8.2m telescope, Spitzer and AKARI infrared satellites, nearby ULIRGs at z<0.3
have been systematically investigated spectroscopically, and Imanishi & his colleagues found that(1) luminous buried AGNs are common in nearby ULIRGs classified optically as non-Seyferts(HII-region or LINER types), and (2) the energetic importance of buried AGNs is relatively higher
in galaxies with higher infrared luminosities, but the star-formation rates are also higher (i.e., morestars will be formed in the future) in these galaxies (Imanishi et al. 2006; Imanishi et al. 2007;
Imanishi et al. 2008; Imanishi 2009).
Their results may observationally support the widely-proposed scenario that the galaxy downsizing
phenomenon, where more massive galaxies with currently larger stellar masses have finished theirmajor star-formation in an earlier cosmic age, is caused by stronger feedbacks from buried AGNs,
which expel or heat surrounding gas in galaxies, stopping further star-formation on a shorter timescale.
26

Both star-formation and SMBH mass growth history have peaks at z>1, so that it is extremely
important to directly investigate the interplay between galaxies and AGNs in this crucial epoch,using the successful 3-35 μm (rest-frame) spectroscopic energy diagnostic method. For this purpose,
infrared low-resolution (R~100) spectroscopy at 6-200 μm in the observed frame (required capability
for SPICA) is the most powerful, and the combination of Safari and MIRACLE onboard the cooled
SPICA mission is clearly the best choice. Herschel lacks wide-band, high-sensitivity spectroscopic
capability. JWST studies of ULIRGs at shorter wavelengths are severely hampered by the large
effects of dust extinction.

Since ULIRGs are, by definition, bright in the infrared, infrared

low-resolution spectroscopy is applicable to a statistically meaningful number of distant ULIRGs at
z>1 within a reasonable amount of telescope time, which is essential but prohibitively difficult atother wavelengths (e.g., (sub)millimeter energy diagnostics using ALMA; Imanishi et al. 2007). For
these reasons, SPICA is clearly best suited to comprehensively understand the interplay between
star-formation and AGNs in the distant universe.
To perform the scientific objectives described above, we will undertake targeted low-resolution
spectroscopic observation with MIRACLE, MIRMES, and SAFARI for statistically meaningful
number of mid-IR selected AGN necessary to discuss their difference with redshift, age, and theenvironment, etc. At the time of the launch of SPICA, not only the targets found by Spitzer, AKARI,& Herschel, but also ones found by JWST will be available. We also emphasize that the mid &far-IR blank-field survey with MIRACLE & SAFARI is quite effective to explore the dusty AGN in
high-z universe, since the emission from dust torus peaks in the rest mid-IR and the mapping speedof SAFARI and MIRACLE is unprecedentedly fast to survey an area at a depth close to the galaxy
confusion limit.

27

Figure Fig.2.2-6: (Left): ULIRGs dominated by star-formation activity. Polycyclic Aromatic
Hydrocarbon (PAH) emission is strong. (Right): ULIRGs dominated by buried AGNs. PAH emission
is invisible.

28

Objective #5: Cosmic Star-Formation & Mass Assembly History
We will reveal the star-formation & mass assembly history of galaxies in relation to theforming processes of the galaxy clusters and the large scale structures, as well as theenvironmental effect on the galaxy evolution.
Our final goal is to understand the cosmic starformation history and its relation to massassembly history of the Universe (i.e. clusterandgroup formation). It is well established thatcosmic star-formation rate density is clearlyhigher in the past Universe, showing a peak at
z~1-2. However, since current surveys of thez>>1

Universe mainly utilize rest-frame UV light, itisalways claimed that MIR-FIR study is essential
because current surveys may have missed alarge amount of “hidden” star formation activity.
Therefore, looking back the distant Universe intheFig.2.2-7 Spatial distribution of MIR-detected

MIR-FIR is a fundamental but an exciting

galaxies (red) around a z~0.8 cluster andapproach to understand the “real” history of the

starburst

galaxies(squares)withclustermember distribution (small dots).

Universe.

However, the situation is even more complicatedbecause galaxy properties (e.g. morphology, colour,star-formation

rate)

are

environment.

In

local

the

strongly

dependent

Universe,

galaxiesoninhigh-density environment such as clusters have little
star-formation activity, but this may not be necessarily
true for the distant Universe. For example, a wide-field
MIR study of a distant cluster at z~0.8 with AKARI findapossiblepeak of star-forming

activity

atthe“intermediate-density” environment such as cluster
outskirts, groups and filaments. In fact, strong dusty
Fig.2.2-8 MIRACLE FoV with a simulation

starburstsof cluster formation by Yahagi et al (2005).

structures around the cluster (Fig.2.2-7). This indicates

JWST/MIRI

that the star formation activity of galaxies may becomparison.

FoV

is

also

shown

as

a

are

distributed

along

the

large-scaleclosely related to the formation of large-scale structuresof the Universe, and therefore we should explore the star formation not only in cluster or general29

fields but along large-scale structures at even higher redshift with SPICA.
Taking advantage of (1) wide-field capability in MIR (MIRACLE) and (2) excellent sensitivity
at λ >20μm (MIRACLE/SAFARI), we can examine dusty star formation up to z~5 based on therest-frame 7.7μm PAH emission (a good tracer of dusty star formation). We show in Fig.2.2-8 theFoV of the MIRACLE with a simulation of cluster formation. It is notable that the 6’ x 6’ FoV of
MIRACLE can well trace large-scale structure surrounding the forming cluster at z~1-5. The mostinteresting targets will be “proto-clusters” at z>2, which are in the early stage of clusters where
many massive galaxies are being formed and possibly tremendous amount of dusty star formation
is taking place. We can detect such population (down to LIRG level) up to z~3 with MIRACLE at
λ~20-40μm. Also, the excellent sensitivity at λ>40μm of SAFARI will give us a great opportunity toextend our study up to z~5. Mapping out the very active star-forming ULIRGs along high-z
structures will be an exciting step and this is accomplished only with SPICA. Here, we note that weneed to collaborate with wide-field ground-based survey (e.g. with Hyper Suprime-Cam to beinstalled on Subaru) to provide good targets of high-z structures for SPICA. At z < 2, the rest-frame
7.7μm PAH shifts to ~10-25μm where JWST is also sensitive. However, the limited field coverage of
JWST makes it difficult to trace whole range of environment around a large sample of clusters (seeFig.2.2-8). We should concentrate on the surrounding region and construct a large sample ofgalaxies at various environments, which will allow us to identify the key environment for galaxy
evolution at every redshift.
Thus, SPICA has unique advantages over other IR missions at all redshifts. We can look back on the
dusty Universe across wide range of environment based on the identical tracer (i.e. 7.7μm PAH) ofdusty star formation up to z~5. We will unveil the importance of hidden activity of galaxies along
the cluster formation history by a wide-fieldsurveyof distant galaxy clusters (and proto-clusters) at

z~1-5

and their surroundings, in comparison with ablankfield survey over sufficiently large Cosmic volume(~106Mpc3). This means that SPICA can constructlarge

samples of galaxies at various redshifts andvariousenvironments very effectively. This will enable us

to

add

the environmental axis in the plot of cosmic
star-formation history (e.g. Fig.2.2-9), which isimportant

step

towards

theFig.2.2-9 The role of SPICA in the objective

complete

understanding of the history of the Universe.

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anDole et al. 2004, ApJS, 154, 87
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31

2.3 Life Cycle of Interstellar Dust
Objective #1: Study of Dust-forming Supernovae
The process of dust formation by massive stars in the ejecta of supernovae in nearby
galaxies is examined based on mid- to far-infrared spectroscopic observations ofseveral (>5) supernovae in nearby galaxies to explore the origin of interstellar dust in
the early universe.
Since after the detection of thermal dust emission in high red-shift universe, dust formation aroundmassive stars has become the object of attention to explore the origin of dust in the early universe due tothe effective feedback of synthesized materials into the ISM in relatively a short timescale (less than
30M☉ even in low metallicity). One of the major processes of dust formation by massive stars is the dust
condensation in the ejecta of core-collapse supernova (SN) explosion. The latest observations with
Spitzer and AKARI reveals, however, the amount of dust newly formed in the ejecta of core-collapse SNeseems to be much smaller than that predicted theoretically. Moreover, we have little observational
understanding on the composition and the properties of newly formed dust in the ejecta of SNe.
Therefore, we propose here the multi-epoch mid- to far-infrared spectroscopic observations of several (>5)
dust-forming supernovae in nearby (<25Mpc) galaxies within 1-2 years after the explosion. We aim to
demonstrate the mid- to far-infrared spectral evolution of dust-forming supernovae in their early epoch
unveiling the dust condensation process in the ejecta gas until it is cooled down to the temperature of
circum-stellar pre-existing dust (~ a few hundred K).

Fig.2.3-1 (a) Three false-colors composite image of the SN2006jc on 220 days after the explosion andthe host galaxy UGC4904 taken with AKARI/IRC 3μm(blue), 7μm(green) and 11μm(red).

(b) Nearto mid-infrared spectral energy distribution of SN2006jc on 220 days after the supernova explosion.
The gray solid line shows the model calculation result of dust thermal radiation. 300K amorphous
carbon dust (green solid line) are found in addition to 800K amorphous carbon dust (red dotted line).
(Sakon et al. 2009)
Figure 1a shows an AKARI near- to mid-infrared image of type Ib supernova 2006jc on 220 days
after the explosion. The red appearance of SN2006jc in the three false-color composite image made32

with 3, 7, and 11μm band data indicates the presence of dust emission around the supernova. The
near-infrared spectra is well reproduced by the 800K amorphous carbon dust which is regarded as
the newly condensed dust in the SN ejecta. Moreover, mid-infrared photometric data indicate excess
emission carried by 300K amorphous carbon dust over the thermal emission of 800K component,
which suggests the dust condensation in the mass loss wind associated with the Wolf-Rayet stellar
activity before the SN explosion (see Figure 1b). In order to distinguish the newly formed dust fromthe pre-existing circumstellar dust and to examine their compositions and the amount correctly,
multi-epoch spectroscopic observations in 5-40μm with high sensitivity are crucial. The obtained

datasets in this study will provide us strong constraints on the composition and the mass of newly
formed dust in the ejecta of various types of SNe in nearby galaxies.
Higher dispersion (R>1000) spectroscopic abilities in the mid- to far-infrared are also effective todetermine the physical condition of the circumstellar materials and to elucidate the transitions
among the gas-phase materials in the SN ejecta, newly condensed dust and its precursory
molecules (e.g., SiO molecules for silicate dust). For example, [SiII] line at 34.82μm and [FeII] line
at 25.99μm are useful to examine the vaporization of pre-existing circumstellar silicate dust and[OIII] line at 88.4μm and [OI] line at 63.2μm are efficiently used to constrain the electron density
and temperature of the emitting region. In order to distinguish the [FeII] line at 25.99μm out fromthe [OIV] at 25.89μm and the [FIV] at 25.83μm, spectral resolution power of R>1000 is required in
the mid-infrared.
This study requires the multi-epoch mid- to far-infrared spectroscopic observations of supernovae ofvarious types in nearby galaxies within 1-2 years after the explosion with high sensitivity in the mid- to

far-infrared. Especially, high-sensitivity spectroscopic abilities in λ>20μm, where MIRMES and
SAFARI onboard SPICA have the great advantages of JWST and Herchell, are crucial to achieve
this project. Moreover, in order to demonstrate the mid- to far-infrared time-variance of dust andgas emission associated with the supernovae, high sensitivity spectroscopy with continuous wider
wavelength coverage from 10-40μm with higher spectral resolution power of R>1000 is
indispensable. We note, since the SNe are the transient phenomena, the loss of the spectroscopic
ability even of overlapping wavelength regime (e.g., 10-20μm) between SPICA and JWST results infatal fault in achieving this project.

33

Objective #2: Dust and Molecular Shells around Low- and Intermediate-mass Stars
Dust formation scenario by low- to intermediate-mass stars is examined based on midto far-infrared imaging and spectroscopy of faint dust and molecular shells around ~30
low- to intermediate- mass evolved objects to explore the origin of dust contained in the
Milky Way and to understand the chemical evolution of ISM in the current universe.
Attempts to understand the dust formation scenario by low- to intermediate-mass stars areimportant to explore the origin of dust contained in the Milky Way and to understand the chemical
evolution of ISM in the current universe. Actually, many observational and theoretical studies haveinvestigated the properties of dust and molecular shells formed in the ejecta gas and/or in theswept-up materials around the evolved low- to intermediate-mass stars such as post-Asymptotic
Giant Branch (AGB) stars and Planetary Nebulae (PNe). It is generally understood that molecules
such as OH, H2O, CO2 and SiO form and O-rich species like silicates dust are expected to condense
when the C/O ratio in the envelope is less than unity and that, on the other hand, molecules such as
C2H2, HCN, C2, CS and SiC form and C-rich species like amorphous carbon, SiC, MgS and PAHs are
expected to condense when the C/O ratio in the envelope exceeds unity. However, the formation andchemical evolution processes of these molecules and dust grains have not yet been fully understoodobservationally. For example, PAH features in the mid-infrared have been observed in the
post-AGB stars and C-rich planetary nebulae, but their existence and/or formation in the gentle
wind of AGB stars have not yet been confirmed possibly due to the lack of ultraviolet photons fromthe AGB stars. For this purpose, mid- to far- infrared (5-200μm) imaging and spectroscopic
observations with high spatial resolution and with sufficient sensitivity are crucial to detect the
faint dust features dominantly powered by soft optical radiations in circumstellar dust shells
around the AGB stars. In this study, we propose mid- to far-infrared high-resolution imaging andspectroscopic observations of faint dust and molecular shells around ~30 low- to intermediate-mass
evolved stars (including AGB stars, post-AGB stars, planetary nebulae, novae etc) in the Milky Way
and in the Magellanic Clouds. We aim to investigate the chemistry and dynamics of the
MOLsphere and its role in the formation of dust grains and to demonstrate the mass-loss history
and the formation process of molecules and dust in the mass-loss wind of evolved stars.
Fig.2.3-2 shows the schematic view of MOLsphere. MOLsphere has been detected in red giants
based on ISO spectroscopic observations but no significant progress have been made since then,although it is expected as a key region to infer the mass loss and34the dust formation mechanisms. Especially,
CO2 (e.g., at 4.27μm and 15.2μm), OCS (at4.89μm) and SO2 (at 7.3μm) are important
molecules to understand the chemistry anddynamics in MOLsphere and high spectral
Fig.2.3-2 --- schematic view of
MOLsphere (see Tsuji 2000)

resolution (R~30000) in 4-20μm is required.
Figure 1a shows an AKARI far-infrared imageof a famous red giant U Hydra.

of warm dust shell, which had been formed about

104

The structure

years before, was successfully resolved.

Fig.2.3-3b shows the 8m Subaru telescope/COMICS 11.7μm image of Galactic planetary nebulaoBD+30 3639 and the detailed structures of PAH emission, silicate absorption as well as of hot dust
continuum emission are discussed. Spatially well- resolved imaging and spectroscopy ofcircumstellar dust shell in mid- to far-infrared are indispensable to investigate the mass-loss
history and chemical evolution (e.g. transition between C/O<1 and C/O>1) in the envelope of
evolved objects.
Izumiura et al.

Matsumoto et al. 2008

Fig.2.3-3 (a) AKARI 90μm image of the
red-giant U Hydra (Izumiura et al.).
(b) Subaru COMICS 11.7μm image of PN

ISAS/JAXA

BD+30o3639 (Matsumoto et al. 2008).

So far only a handful of bright evolved objects have been spatially resolved in the mid- to
far-infrared. In order to resolve the faint diffuse dust and molecular shells around larger number ofother evolved objects in the Milky Way and in Magellanic Clouds, imaging and spectroscopic
capabilities with high spatial resolution and high sensitivity in 5-200μm achieved by >3m classspace infrared cryogenic facility are required.
Mid- to far-infrared imaging capability with high spatial resolution and high sensitivity of
MIRACLE and SAFARI onboard SPICA are quite useful to demonstrate the dynamical andchemical process in which the newly formed dust in circumstellar environment is ejected into theinterstellar space. Moderate-dispersion (R>600-1000) spectroscopic abilities in the mid-infraredwith MIRMES and in the far-infrared with SAFARI is crucial to examine the physical conditions
and chemical composition of the circumstellar gas, molecules and dust grains around the evolved
objects. High-dispersion (R>10000) spectroscopic abilities in the mid-infrared 4-20μm with
MIRHES is important to examine the properties of molecules in MOLsphere of redgiant. Neither
JWST nor Herchel has the sufficient capability to complete this study.

35

Objective #3: Dust formation and grain growth in Dense Molecular Clouds
Dust formation and grain growth in the dense molecular clouds are examined based on
mid- to far-infrared spectroscopic observations of ~30 molecular clouds with embedded
young stellar objects in the Milky Way and in nearby galaxies
Theoretical studies indicate that the interstellar dust is replenished by stellar dust sources (SNe,AGB stars, etc) in a typical timescale of 5×109 yr and that it is destroyed by SN shocks in much
shorter timescale of <1×109 yr. This suggests the existence of another dust formation sequence,
which should be more effective than that occurring in the mass-loss wind of evolved stars.
Glass with Embedded Metals and Sulfides (GEMS) is a particle found in the Interplanetary Dust
Particles (IDPs). Figure 1 shows the infrared spectra of GEMS in IDPs, laboratory spectra of troilite(FeS) and pyrrhotite (Fe1-xS), and “23.5μm” band spectra found in the ISO SWS spectra of AB
Aurigae and HD163296, young stars embedded in dense molecular clouds. Close resemblanceamong these spectra indicates the link between the dust in dense molecular clouds and the GEMS
in IDPs. Since sulfur is largely depleted in dense clouds and not in the general ISM (see Fig.2.3-5),
incorporation of sulfur in GEMS in dense clouds is suggested. Therefore, dense molecular clouds
with embedded young stellar objects in the Milky Way and in nearby galaxies are favorable places
to look for iron sulfides.

Figure Fig.2.3-4 (left panel) Glass with Embedded Metals and Sulfides (GEMS)
in Interplanetary Dust Particles (IDPs) (Bradley et al. 1999). (right panel)Comparison of “23.5μm” features in laboratory infrared spectra of troilite (FeS)and pyrrhotite (Fe1-xS), the infrared spectra of sulfide-rich IDPs (L2011*B6,U2012A-2J), and the ISO SWS spectra of two young stars AB Aurigae andHD163296 after subtracting the model spectra composed of amorphous silicates,
metallic Fe and carbonaceous materials and water ice (Keller et al. 2002)

36

Fig.2.3-5 (left panel) Depletion of elements in general ISM. Little depletion isindicated for sulfur (Savage & Sembach 1996). (right panel) Depletion of elements
in dense molecular clouds. This time, on the other hand, significant depletion isindicated for sulfer (Joseph et al. 1986).
In this study mid- to far-infrared spectroscopic observations of ~30 dense molecular clouds withembedded young stellar objects in the Milky Way and in nearby Galaxies are proposed to detect the
infrared bands of iron sulfide grains and to demonstrate the connection between the GEMS in IDPs
and the interstellar grains. The presence of 23.5, 34, 38, 44μm features carried by iron sulphides(e.g., troilite FeS) are searched in the mid- to far-infrared (20-45μm) spectra of dense molecular
clouds, in which the enhanced depletion of sulfur to dust grains are suggested. Then we try tosystematically understand the role of cold dense molecular clouds as the site of dust synthesis
and/or the grain growth.
This study requires high sensitivity for diffuse emission, especially, in 20-45μm, the core spectral
range of SPICA. Neither JWST nor Herschel has the required capability. Moderate-dispersion(R>~1000) and high sensitivity spectroscopic abilities in the mid-infrared (10-36μm) with MIRMES
and in the far-infrared (35-200μm) with SAFARI are crucial to identify the mid-infrared features ofiron sulfide grains at 23.5 μm, 34 μm, 38 μm and 44μm. High-dispersion (R>10000) spectroscopic
abilities in the mid-infrared (4-20μm) with MIRHES is crucial to examine the properties ofmolecules in dense molecular clouds and their chemical evolution including the formation of icy
mantles onto the dust grains. Especially, collaboration with ALMA project is quite useful toobservationally demonstrate the detailed chemical synthesis of organic molecules on the surface of
the icy mantle.

37

Objective #4: Study of Supernovae Remnants
The effects of supernovae on the material evolution in the universe are investigated bymid- to far-infrared imaging spectroscopic observations of about 50 supernova
remnants that are detected in the infrared with spotlighting the formation anddestruction of dust grains and the energy supply to the ISM.
Supernovae (SNe) are the major factory of heavy elements and play a vital role in the various key
processes in the material evolution in the universe.

In particular, theoretical investigations

suggest that SNe make significant contributions both to the formation and destruction of dust
grains.

However recent observations of Spitzer and AKARI indicate that dust may not be formed

efficiently in SN explosions, whereas very few observational studies have been carried out for thedust destruction by SN shocks.

Infrared is the best spectral range to investigate the properties ofdust grains and the interaction of SN shocks with the surrounding medium.

We propose here to

make a systematic infrared study of supernova remnants (SNRs) and investigate the dust
formation and destruction in SNe as an important part of the study of the life cycle of interstellar
dust.

It is complementary to Object #1 (observation of supernovae).

SNRs show complicated structures in the infrared.
image of the young oxygen-rich SNR G292.0+1.8.

Fig.2.3-6(a) shows an AKARI mid-infrared

The ring-shaped structure seen in the middle ofthe image (ER) comes from the emission of dust grains formed before the SN explosion. The
emission from dust grains associated with the SN ejecta appears clearly in the 15 to 24m band
intensity ratio map (b).

Fig.2.3-6(c) shows the spectra of the ejecta, indicating the presence of abroad feature around 18m that contributes to the increase in the band ratio.

Other oxygen-rich

SNRs also indicate
(a)

(c)

(b)

Fig.2.3-6 AKARI 7, 15, and 24μm artificial color image (a) and the 15 to 24μm band intensity ratio(b) of SNR G292.0+1.8 (Lee et al. 2009).

The SN ejecta is clearly seen in the ratio image.

(c)

Spitzer IRS spectra of the ejecta in G292.0+1.8 (Ghavamian et al. 2009). A broad feature is seenaround 18μm.
the presence of a broad feature in 18–23μm region, suggesting common properties of dust grains
38

associated in SN ejecta, but no firm identification of the carriers have so far been established.
These observations demonstrate the importance of high-spatial resolution observations to separate
each component and extract the emission from the SN ejecta and the significance of
medium-resolution spectroscopy of SNRs to correctly understand the nature of the infraredemission and dust properties in the SNRs.

Similarly high spatial resolution is strongly required in

the far infrared to fully understand the nature of SNR emission and investigate the presence of cold
dust associated with SNRs.

A wide spectral coverage from the mid to far infrared is crucial tounderstand spectra of SNRs that consist of dust bands as well as emission lines. Full infrared
spectra of the interacting region of SN shocks (a shell-like emission in Fig.2.3-6(a)) are also
important to study the size distribution of dust grains and thus the dust destruction process.
Spectroscopy also tells us gas chemistry taking place inthe ejecta as well as in the interacting gas.

Fig.2.3-7

shows an infrared spectrum of a knot in the Cas A SNR,
suggesting the presence of CO gas. The detection of CO
gas is significant since some theoretical work predicts
direct condensation of carbonaceous dust from carbon
gas without forming CO.

If CO is formed in the ejecta,

the formation of carbonaceous dust is largely reduced.
Fig.2.3-7 AKARI spectrum of a knot in

Similarly, observations of SiO gas band around 8μm are

the Cas A SNR.

valuable for the study of silicate dust formation.

CO gas emission

feature in 4.4–4.7μm is clearly seen.

High-resolution spectroscopy of these bands enables us
to

make

detailed

investigations

of

the

physicalconditions and gas chemistry in SN ejecta. High-resolution spectrograph in the 4–8+α μm region
thus provides unparalleled information on the study of dust formation process in SNe.
This study requires high sensitivity for diffuse emission from the mid- to far-infrared, the core
spectral range of SPICA.

Neither JWST nor Herschel has the required capability.

High spatial

resolution in the mid to far infrared is indispensable to separate the various components andspectroscopic imaging capability for an arcminute scale is important.

Imaging spectroscopy

capability with sufficient spatial resolution and high sensitivity for diffuse emission of MIRACLE,MIRMES, and SAFARI onboard SPICA provides the unprecedented opportunity to execute thisstudy.
Study of Young Core-collapse Supernova Remnants with FPC-S
We propose FPC-S spectral mapping of young core-collapse SNRs in the Galaxy in order to study
the SN explosive nucleosynthesis and explosion process. The explosion of core-collapse
supernova(SN) is known to be asymmetric and turbulent, but the physical mechanism and the
explosion process remain to be largely unknown. The young Galactic SNRs provide an unique39

opportunity to study the detailed spatial and kinematical distribution of ejecta. For example, in the
3,000-yr old SNR G11.2-0.3, [Fe II] emission line observations revealed that the Fe ejecta from theinnermost layer of the explosion are both spatially and kinematically asymmetric (Koo et al. 2007,
Moon et al. 2009). The Fe ejecta do not show other heavy elements which indicates the production
without intense microscopic material mixing as in alpha-rich freezeout process. A similar
asymmetric distribution of ejecta has been observed in another young SNR G292.0+1.8 using the
AKARI infrared space telescope (Lee et al. 2009). The LVF observation can provide unprecedented
information on the distribution of ejecta material produced in core-collapse supernova explosion as
well as that of the circumstellar material from progenitors.
There are many important elements of the ejecta and circumstellar material that can beobserved in the near-infrared wavebands. The ejecta usually have significant amount of Fe, S, Si, O,
and/or He from the supernova nucleosyntheses, and all of them have bright emission lines in thenear-infrared wavebands. H, H2, and/or He from the circumstellar material of the progenitors also
have strong near-infrared transition lines. Considering that young core-collapse SNRs are locatedin the Galactic plane where there are numerous stars overlapping, it is critical to subtract out thestellar radiation using the nearby continuum emission to identify the line emission of the ejecta andcircumstellar material. The LVF spectral mapping naturally provides such a capability of obtaining
nearby continuum emission with the same point spread function of the line transitions.

40

Objective #5: Interstellar Medium in Nearby Galaxies
By mid- to far-infrared imaging spectroscopy, we spectrally decompose and spatiallyresolve emission from the ISM in 50 nearby galaxies of our AKARI sample, to track
galactic-scale material circulation from sources to sinks of the ISM in galaxies.
The physical processing and chemical evolution of the ISM in galactic scales are examined in viewof material circulation within nearby galaxies. From this viewpoint, “sources” of the ISM include
SNR, giant molecular clouds, environments around evolved stars, outflows from galactic nuclei,
accretion of intergalactic matters, and mergers of galaxies, while “sinks” of the ISM are such as
shocked regions, nuclear activities in jets and X-ray, hot plasmas, and galactic outflow. By spatiallyresolving these components from diffusely extended components, we track the large-scaletransmigration of dust and the gradient of ISM properties within a galaxy. Since the evolution ofdust highly depends on the phase of associated gas, we spatially decompose the phases of molecular,
atomic (including PDR), and ionized gases by spectral line diagnostics to obtain the density andtemperature of gas. With MIRACLE and SAFARI, we derive large-scale spatial information over awhole galaxy, while MIRMES probes local regions such as galactic nuclei (and SSCs) to study theproperties of LINERs and nuclear starburst as well as the effects of nuclear activities on ambientmaterials.
The wavelength range of 20-200 micron, in which SPICA has high sensitivities, is suitable for studyof the ISM associated with high-energy phenomena such as shocks, plasma/X-ray heating, galactic
super-wind, and nuclear jets, providing knowledge complementary to cold matters (Herschel,
Planck, and ALMA) and stars and PAHs (JWST). In particular, the 35-55 micron range that neither
Spitzer nor Herschel can cover is the key to understand spatial variations in the chemicalcomposition (silicate, carbonaceous) and size distribution (sputtering, fragmentation, aggregation)of dust.

Fig.2.3-8 Edge-on disk galaxy NGC253. (a) AKARI 9um (PAH+old stars). (b) 18um (warmdust). (c) VLA 20 cm continuum. Discrete radio sources: SNRs? HII regions? (d) AKARI
90um in color, ROSAT X-ray in contours. Dust outflow entrained by X-ray superwinds.
The objective can be categorized into two big themes: (1) 3D picture of ISM distributions in various
gas phases, and (2) galactic nuclei and influence of their activities on ISM, AKARI examples of41

which are shown in Fig.2.3-8 and Fig.2.3-9, respectively. For the former, MIRACLE and SAFARI(low-res.) enable spatially-resolved spectroscopic studies of dust and gas in disks and haloes forface-on and edge-on galaxies. For the latter, MIRMES and SAFARI (high-res.) probe central regionsof galaxies by detailed gas line diagnostics, even revealing the kinematics of material circulationflow.
Based on our AKARI nearby galaxy sample, we carefully select 50 target galaxies for SPICA, whichhave sizes of 5-10 arcmin with various morphological types. We require 600 hrs in total, thebreakdown of which is 4, 1, and 7 hrs per galaxy for MIRACLE, MIRMES, and SAFARI, respectively.
In the final decision of target selection, we will, of course, account for new knowledge to be revealed
by upcoming observatories such as Herschel, JWST, and ALMA.
Why do we need SPICA other than Herschel and JWST? There are mainly two reasons: (1) low FIR
background thanks to the cold telescope enables faint extended emission to be detected from nearby
galaxies, which Herschel cannot detect. (2) Small and simple PSFs in the MIR-FIR thanks to themonolithic 3.5m mirror can reliably resolve various dust and gas components in nearby galaxies.
Our requirements for SPICA are as follows:(1) MIR-FIR continuous spectral coverage is crucial for dust physics, maximizing outputs from thecold telescope; this would make SPICA unrivalled.
(2) MIR-FIR spectroscopic imaging capability with low - moderate spectral resolution is essential
for spatially-resolved studies of nearby galaxies.
(3) For efficient mapping, we need the capability of raster mapping with variable integration time
at different positions.
(4) For better calibration of extended sources, [SiII] 34.8 μm line should be observed by both
SAFARI and MIR instruments with matched spectral capabilities. Two different modes arecompared: imaging FTS and long-slit spectral mapping.

Fig.2.3-9 : LINER elliptical galaxy NGC1316. AKARI/FIS 4-band contours overlaid on
AKARI 11um image. Energy feedback outflow from a central dust reservoir (Temi et al.
2007)

42

Objective #6: Imaging and Spectroscopic Survey of Galactic Plane
Structures and constituents of the Milky Way are illustrated in detail by exploiting an
imaging survey covering the region of -90o<l<+90o and -2o<b<+2o in several
mid-infrared bands and a spectroscopic survey covering the region of -60o<l<+60o and-1o<b<+1o in the mid-infrared. The life cycle of the interstellar medium in the Milky Way
is examined on a galactic scale in terms of the activities of low-mass to massive stars.
For the thorough understanding of the circulation and physical/chemical evolution of matter in the
Galaxy, we need to know the distribution of each population of mass-losing objects, including
low-mass RGB and AGB stars, massive Wolf-Rayet stars, luminous blue variables, supernovae, andso on. High mass-loss rate stars that are preferentially found near the Galactic center may
dominate the mass and dust return rates in that local space.
Besides, knowledge on the shape of the Galaxy, as a result of the synthesis of all kinds of stellar
populations, is also indispensable for understanding the matter circulation in the Galaxy.

It iswell accepted that our Milky Way Galaxy is a spiral galaxy with a thin disk of stars and gas
rotating about the Galactic Center. There are accumulating pieces of evidence that the Milky Way
Galaxy has a bar structure in its center (Binney et al. 1991; Blitz & Spergel 1991; Nakada et al.
1991; Stanek et al. 1994) and the bar may have an additional finer structure (Nishiyama et al. 2005,
Fig.2.3-10, and references therein). GLIMPSE surveys with the Spitzer Space Telescope (Benjaminet al. 2005, Fig.2.3-11) revealed a stellar bar structure in the near-side of the Galactic disk withrespect to the Galactic Center. Their survey, however, suffers source confusion that hampers thedetection of the far side of the bar structure. Also, the stellar spiral pattern of the Milky Way
Galaxy still remains controversial (e.g. Benjamin et al. 2009).
To obtain a correct view of the distribution of dust-supply stellar sources in our Galaxy we
propose to make a MIR Galactic plane survey with SPICA. The MIR (Mid-Infrared), the essential
waveband for the census of mass-losing objects in the Galaxy, is not accessible with coming
cutting-edge facilities such as Herschel or ALMA. The proposed survey consists of imaging andspectroscopic observations. Spitzer GLIMPSE survey (Benjamin et al., 2003) has a limiting
magnitude of 0.4 mJy at 4.5 μm (Mead et al., 2005). It is also confused with sources in the Galactic
plane. The flux of red clump stars at the other edge of the Galactic disk is estimate to be about 70
μJy (5 σ) at 5 μm, including the interstellar extinction. The source density down to this flux level is
extrapolated from GLIMPSE data (Benjamin et al., 2005) to be 0.2 sources in one arcsec^2.
Therefore SPICA survey will not be limited by confusion. The flux level of 70 μJy should be reached
in a net integration time of 3 sec with MIRACLE. Ergo, the imaging survey to detect all red-clump
stars in our Galaxy can be completed in a relatively short time if an efficient survey capability of
SPICA is equipped. For the imaging survey we propose to cover the region of −90o < l < +90o and43−2o< b < +2o. We also propose to make about 10 repeated observations to monitor the variability.
The imaging survey will provide us with the structure of our entire Galaxy, including the bar, bulge,
and arms and the distribution of dust supplying sources in our Galaxy. We expect to detect one
billion sources in this survey. In addition, a supplemental imaging survey of the same region at~4μm with a similar sensitivity with FPC-S will further enhance the scientific capabilities of the
MIRACLE imaging survey, if available.

The wide field of view of SPICA is a great advantage toother mid-infrared space missions with a comparable spatial resolution.
The spectroscopic survey makes use of the multi-slit of MIRACLE and obtains spectra for theregion of -60o < l < +60o and −1o< b < +1o. With the net integration time of 3 sec per slit position, we
would like to reach 600 μJy (5 σ) at 5 μm. Again we need an efficient slit scan capability with
MIRACLE of SPICA, which would be a tough requirement for SPICA. The spectroscopic survey is
expected to detect one million sources, including very luminous red objects, which allows us toobtain the distribution of mass-losing massive stars in our Galaxy for the first time. It will also
provide a complete diffuse emission map of the Galactic plane. Combining the results of this survey
with the detailed study of SNe, SNRs and low-mass evolved stars, we will be able to obtain the fullunderstanding of the contribution of each stellar source to the dust supply at every position of theinner part of our Galaxy. The planned multi-slit function in spectroscopy of MIRCLE makes SPICA
a unique space mission at mid-infrared.

Fig.2.3-10 Peak magnitude of red
clump

star

countsagainstthe

Galactic longitude (Nishiyama etal.2005). Changes in the slope of theplot indicate the presence of an inner
structure in the central bar of thebulge.

44

Fig.2.3-11 Power-law exponent ofsource counts as a function of flux
density, plotted as a function of the
Galactic longitude and apparent
magnitude (Benjamin et al. 2005).
Upper panel: Positive longitude,
lower pane: Negative longitude.
The features in yellow-orange anddark blue together in the upper
panel indicate the detection of acentral stellar bar.

45

References
Benjamin 2009, in The Galaxy Disk in Cosmological Context , IAU Sypm. 254, eds. J.
Andersen, J. Bland-Hawthorn, and B. Nordström, p. 319-322
Benjamin et al. 2005, ApJ, 630, 149
Benjamin et al., 2003, PASP, 115, 953
Binney et al. 1991, MNRAS, 252, 210
Blitz & Spergel 1991, ApJ, 379, 631
Bradley et al. 1999, Science, 285, 1716
Ghavamian, P. et al. 2009 ApJ, 696, 1307
Izumiura et al. 2009, in prep.
Joseph et al. 1986, ApJ, 309, 771
Keller et al. 2002, Nature, 417, 148
Lee, H.-G. et al. 2009, ApJ, submitted
Matsumoto et al. 2008, 677, 1120
Mead et al. 2005, GLIMPSE Legacy Science Data Products (ver. 1.5; Madison:
Dept. Astron.,

Univ. Wisconsin)

Nakada et al. 1991, Nature, 353, 140
Robitaille et al., 2007
Sakon et al. 2009, 692, 546
Savage & Sembach 1996, ApJ, 470, 893
Stanek et al. 1994, ApJ, 429, L73
Temi et al. 2007, ApJ, 666, 222

46

2.4 Studies of Exoplanets and Solar Systems
Objective #1: Direct Detection and Characterization of Exoplanets
To understand the diversity of the exo-planetary systems, we will attempt direct
detection and characterization of exoplanets in the infrared wavelengths. Complement
al two methods, coronagraphic observation and planetary transit monitoring, aredescribed as key observations.
(Introduction)
The solar system including the Earth;
Is such a system unique in the Universe, or is it commonplace?
How is such a planetary system born and evolved?
We consider these are ones of the most important questions for space science in the near future,potentially connected to the search of the origins of life. Since the first report by Mayor and Queloz(1995), more than 300 exoplanets have been found. However, most of the detections are by indirect
methods, e.g., detail monitor observation of radial velocity of a mother star. For the next step, we
need observations which make the systematic characterization of Jovian exoplanets (one of themost major elements of planetary system) possible. When such characterization is attempted,
usually huge contrast between a mother star and a exoplanet is critically serious problem.
(Observation requirement ; Why SPICA?)The contrast is relaxed in mid-infrared wavelength rather than optical wavelength because ofthermal infrared emission from a planet as shown in Fig.2.4-1, which also shows there areimportant spectral feature of Jovian exoplanets in mid-infrared. So the capability of mid-infrared(>3.5 µm) observation is needed. For the characterization (not only the detection) of the exoplanets,
we require spectroscopy with the spectral resolution of 20-200 in order to measure spectrum of
exoplanets including features of CH4, NH3, H2O and so on. To improve sensitivity in order toobserve old (a few Gyr) Jovian planets in shorter wavelength than 5um, it’s preferable to use a InSb
detector together with a Si:As detector. HERSCHEL does not have sensitivity in mid-infrared.
Mid-nfrared sensitivity of groud-based giant telescopes of the next generation (e.g., TMT) is quite
limited because of huge infrared emission from the sky and telescope itself. After all, only JWST canbe a rival of SPICA. Strategy to go over JWST is described below with each observation method.

Coronagraphic observation
Direct imaging and spectroscopy by a coronagraph is the most straightforward way to the detection47

and the characterization of the exoplanets. Recent papers reported the success of direct imaging ofseveral exoplanets (Marois et al. 2008, Kalas et al. 2008, Fig.2.4-2) using ground based telescopewith adaptive optics and Hubble Space Telescope (HST) in near-infrared and optical wavelength.
However, such examples are strongly limited in only luminous planets far from the mother star andspectroscopy is not achieved. These examples make significance of SPICA coronagraph more surebecause they do provide evidences of existence of targets, and concrete information of detection forupcoming characterization with SPICA. For SPICA coronagraph, required contrast in PSF, andinner working angle is 10-6, and 3.3lambda/D, respectively, to perform coronagraphic observation for
significant number of (~100) targets. Broad bandpass filters are needed for the coronagraphic
imaging mode. Major advantage of SPICA coronagraph over JWST’s one are 1)Thanks to the clean
PSF by monolithic telescope mirror and active optics, the contrast of SPICA coronagraph will be~10times higher than JWST’s. 2)Continuous wavelength coverage of spectroscopy. Use of InSb
detector together with Si:As detector is also useful for differential observation in two closed bands
simultaneously, which improves contrast by image subtraction.
Monitor observation of the planetary transit
Another hopeful way for the characterization of spectrum of the exoplanets is the monitor
observation of the planetary transit. It was shown by observations with SPITZER space telescopethat absorption feature by atmosphere of an exoplanet is detectable by non-spatially resolved
monitoring of transiting planetary system (e.g., Deming et al. 2005).

Recently detection ofimportant features, e.g., H2O, are reported (e.g., Tinetti et al. 2007). At current succeeded targets ofsuch observation are limited “hot Jupiter”. SPICA can extend the targets of spectroscopic study ofplanetary transit toward smaller planets vastly because of photon gathering power by larger
telescope aperture than SPITZER. To realize systematic study by this method, spectroscopy with

R~200 or more is needed. Strategy to avoid saturation in the detector and achieve high duty-cycle isimportant. Stability of the observing system is essentially important. The coronagraph instrumentwith coronagraph-mask removed mode (i.e., fine-pixel camera mode) can be also useful tool for thispurpose, in which instrument design against the saturation problem (e.g., defocusing function) andinternal calibrator will be adopted. InSb detector extends spectral coverage of this observation tonear-infrared region. Instrument designed considering saturation problem, stability calibration,and simultaneous wide-spectral range monitoring by two detectors can be advantage of SPICA over
JWST for the planetary transit monitoring. Targets of this study have to be discovered before. Space
telescopes, COROT, Kepler, and projects using ground-based telescopes will provide much enoughnumber of detection of planetary transit via ongoing or upcoming operation. The coronagrahpic
observation and the planetary transit monitoring are complementary because the former and later
method is suitable for distant and closed planet from the mother star, respectively.

48

49

Fig.2.4-1 Spectrum of Jovian exoplanets derived by simulation (left: Burrows et al.
2004, right: Burrows et al. 1997)

Fig.2.4-2 Directly imaged exoplanets. (left: Marois et al. 2008, right :Kalas et al. 2008)

Fig.2.4-3 Left: Planetary transit data to derive infrared spectrum feature (Deming et al. 2005).
Right: Spectral features of an exoplanet derived from the transit monitor detecting H2O (Tinetti etal. 2007).

50

Objective #2: Dissipation of Gas from Proto-planetary Disks
We will reveal the formation mechanism of gas giant planets and initial condition ofterrestrial planet formation, by observing the dissipation of gas and their structural
evolution in planet-forming regions.
For the last decade, more than 300 gas-giant planets have been discovered by measuring the radial
velocity of parent stars. It is intriguing that many of them have orbital period much shorter thanJupiter on our solar system, and also a variety of orbital eccentricities. In contrast, coronagraphic
imaging at optical and near-IR wavelengths have revealed promising candidates of extrasolar
planets, whose orbital scales are larger than Jupiter. Forthcoming space missions like Corot and
Kepler would even discover a number of terrestrial planets in the next several years.
The best examination of their formation and evolution theories require the observations ofcircumstellar disks in active planet-formation. The evolution of the disk at r=1-30 AU is ofparticular interests for investigating planet formation like our solar system,

orbital migration ofgas-giant planets, and formation of extrasolar terrestrial planets. Spectroscopic capability of SPICA(MIRMES, MIRHES, SAFARI, BLISS) will provide an excellent opportunities for observing gas insuch regions. Such studies are complementary with (1) ongoing studies of disk structured bymeasuring spectral energy distribution of gas disks; (2) ALMA, which will allow us to resolve thestructure of dust disks at AU scales in nearest planet forming regions; and (3) JWST, whose
spectrographs have unprecedented sensitivity at λ<20 μm with a spectral resolution up to R=3000.
The gas comprises most of the initial disk mass and may consequently play an important role in theformation and evolution of planetary systems. It would allow gravitational instability to occur for
the formation of gas-giant planets (e.g., Boss 2003), or provide gas drag on rocky materials,
determining the mass and orbital eccentricities of terrestrial planets (e.g., Kominani & Ida 2002).
So far, observational studies of gas disks have been conducted mainly through radio interferometry
and ground-based optical-IR spectroscopy. The former technique allows us to observe regions on a
few hundred AU scale (Dutrey et al. 2007), while the latter allows us to observe regions within a few
AU from the central star (Najita et al. 2007). Recent advances in mid-to-far IR spectroscopy haveallowed us to explore the gas at intermediate radii from the star (i.e., 1-30 AU), the key zone forunderstanding planet evolution. Such studies to date include: (1) Spitzer spectroscopy of atomic([Ne II], [Fe II] etc.) and molecular lines (H2O, OH, HCN, C2H2- e.g., Lahuis et al. 2007; Carr &Najita 2008; Salyk et al. 2008) and (2) ground-based observations of [Ne II] and H2 17 μm (e.g.,
Herczeg et al. 2007; Bitner et al. 2008) 5. The spectrographs discussed for SPICA are well optimized
to extend such research to truly discuss the evolution of gas disks due to planet formation.
MIRMES, SAFARI and BLISS would detect emission lines over a wide-spectral range (10-200 μm)
at an unprecedented sensitivity, being free from telluric absorption. The coverage of these
spectrographs include a variety of atomic/ionic/molecular lines expected from the protoplanetary51

disks (Fig.2.4-4). This would allow us to measure the total mass of gas with many young stars witha variety of evolutionary phases. As a result, we would be able to determine the dissipation time of
the gas disk at 1-30 AU, and its relationship with stellar mass and binarity. Such observations
would provide crucial information for identifying the formation mechanism of gas-giant planets,
and initial conditions of terrestrial planet formation.
MIRHES would be sensitive to the profiles of various emission lines, leading to the determination ofphysical/chemical conditions as a function of radius. To facilitate this, its spectral coverage isdesigned to observe a variety of emission lines (CO, H2O, HCN, CO2, C2H2 etc.) at 4-8 and 12-18 μm.
This would allow us to observe how the structure of gas disks evolve due to planet formation(Fig.2.4-5).

Fig.2.4-4: modeled spectrum of a relatively evolved protoplanetary disk (M ~1 M solar, t~10 Myr, left),and predicted line fluxes as a function of gas mass (right) (Gorti & Hollenbach 2004). The reddashed lines indicate the sensitivity of SPICA (1 hr, 5-σ at 140 pc).

Fig.2.4-5 (left) a variety of molecular lines associated with a protoplanetary disk. Adapted from
Spitzer Press Release. (top-right) Numerical simulation for a protoplanet tidally interacting with a52

protoplanetary disk and opening-up a disk gap (Bryden et al. 1999). (bottom-right) Schematic viewof how the disk clearing due to a proto-Jupiter would change the emission line profile.

Objective #3:

Debris Disk Surveys

We reveal the similarity or diversity of extrasolar systems by observing a number ofdebris disks, which are much more easily observable than exoplanets.
Not only the molecular gas but also dust grains play the key roles in the evolution of circumstellar
disks and the planet formation, since all planets are thought to form in the accretion disks thatdevelop during the collapse and infall of massive dusty and molecular cocoons larger than ~10 000
AU where stars are born.
The young disks are very optically think in dust, with high radial midplane optical depths in thevisual (τV >> 1). These protoplanetary disks then start to become optically thin (τV ~ 1) in a few
million years after formation and evolve into transitional discs as their inner regions begin to clear
at >10 Myr. Disks with ages above >10 Myr are thought to be practically devoid of gas (Duvert et al.
2000) and the dust in these older debris disks is generally not primordial but continuously
generated “debris” from planetesimal and rocky body collisions. At this stage, the disk becomes very
optically thin (τV << 1). Debris disks are thus younger and more massive analogs of our own asteroid(hot inner disk, Td ~200 K) and Kuiper belts (cool outer disc, Td =~ 60 K), so their study is vital toplace the Solar System in a broader context.
SPICA is also capable to survey existence of such dust disks in our Galaxy, with extremely highsensitivity in the mid and far-infrared.
Debris Disk Survey in the Solar Neighborhood
A number of dusty debris disks have been discovered to date since the initial IRAS identificationof an infrared excess from the A-type main-sequence star, Vega. While most pre-main sequencestars host a dust disk, a recent census by Spitzer Space Telescope suggests that 10-15 % of nearby
main sequence stars host such disks, independent of spectral types. They have given very important
information on what is happening during early stage of planet forming processes. However, they
comprise only a small portion of the whole extra-solar systems: debris disks discovered so far arevery bright ones due to limited capability of the telescope/instruments.
SPICA’s unique capabilities of high sensitivities at FIR and a coronagraph at MIR enable us todetect debris disks around nearby normal stars as faint as our Solar system’s by imaging
observations.

It may not be easy to detect Zodiacal light equivalents around Asteroid Belt evenwith SCI due to the limited spatial resolution. However, since all the extrasolar planetary systems
do not always have the identical architecture, it is worth trying to detect debris disks in the MIR
with SCI. Kuiper Belt debris should be detected with SAFARI if it is equipped with a simple
53

coronagraph. The faint debris is most likely produced by mutual collisions of less disturbed small
bodies like our own, and provides us with clues on current status of planet formation. The location(radii) of the debris disks (rings) give clues to current disposition of planets.

Although they may

not be direct evidences of the presence of plants, we can obtain a lot of circumstantial evidences forthe architecture of the extrasolar planetary systems.
Targets are almost all normal stars (of about 30-50) closer than a certain distance which is < 5pc.
They should be chosen from the latest list of nearby stars before the observations.
A coronagraph mask is required to overcome possible limited dynamic range of SAFARI.
Statistical Study of Debris Disks around Early type Main-Sequence Stars
The number of detected debris disks is increasing but is still far from satisfactory when making
statistical discussions.
a factor of 10.

The sensitivity of SPICA at FIR will be higher than AKARI and Spitzer byThus, it will potentially increase the sample of debris disks dramatically.

However,just a high sensitivity is not enough to detect faint debris disks because a debris disk is detected as
an excess over the stellar photospheric emission. In order to detect small excess emission,
photoshperic emission should be accurately estimated based on the observations at shorter
wavelengths and model stellar atmospheres but the accuracy is at best only a few percent. Below
this level, it is detection of excess emission is not practical even if the sensitivity is high enough.
Therefore, best strategy utilizing high sensitivity of SPICA at FIR is to try to detect debris diskswith large fractional excesses (relative to the stellar photospheres) at large distances, i.e. a volume
limited debris disk survey. With a limited available observing time, higher detection rate ispreferred. Early type stars (A and F types) are the most promising targets because they areassociated with bright debris disks more frequently than other spectral type stars. Targeted
observations of carefully selected A type stars within a few kpc will provide statistically uniform
samples.

This data set will dramatically increase bright debris disks around A type stars andenable us to study early phase of planetary system formation of early type stars statistically. Solartype stars (G type) are more important because they provide more direct information about
formation process of our own solar system but bright debris disks are rarer than early type stars.

54

Fig.2.4-6 Spectral energy distributions of debris disks at distances 1, 2.5, and 8kpc compared withSPICA/SAFARI (SOAP & GOAL) sensitivity as well as JWST/MIRI and Herschel/PACS.
Objective #4: Role of Ice for Planet Formation
We will reveal the distribution and crystallinity of water ice in the disk, and investigate
role of ice for planet formation, and how the elements for originating and sustaining life
could be supplied to terrestrial protoplanets.
Water ice is supposed to play a significant role in the formation of planets. Below gas temperaturesof ~150 K, water vapor freezes out and the main form of water in the cold disk midplane and atlarge disk radii will be ice which determines the
position of the so called “snow line” (the water ice
sublimation front; see figure). Grains covered bywater icy mantles enable the formation ofplanetesimals and the core of gas giants beyond

thesnow line, which separates the inner disk regionofterrestrial, rocky planets from that of the outergas

giant planets. Furthermore, it is possible thatduring the later phases of planetary formation,

theatmospheres, and indeed the oceans, of the rocky
planets are formed by bombardment of comets

Fig.2.4-7 position of “snow line”
andasteroids which contain water ice. However, very little is known or constrained from observational
point of view. It is partly because water ice grains have spectral features at ~44 μm and ~62 μm
that are difficult to be accessed so far.
SPICA enables us to access various water ice features especially at ~44 μm (never accessed since55ISO) and ~62 μm. In particular 44 μm water ice feature is a powerful tool to investigate thecrystallinity (crystal or amorphous) of water ice and its temperature. For most disk sources, it is
impossible or very difficult to use MIR absorption features to trace water ice and the material is toocold to emit in the NIR/MIR bands. Hence, these strong FIR features are robust probes of (1) the
presence/absence of water ice, even in cold or heavily obscured regions without a MIR background,and (2) the amorphous/crystalline state which provides clues on the formation history of water ice
and origin of comets. Note that JWST can not access these solid state bands and Herschel only has
access to the ~62 μm band with much poorer sensitivity and limited bandwidth. Therefore, ice
spectroscopic survey with SPICA/SAFARI towards a broad range of environments (such as
protostellar envelopes, circumstellar disks, and solar system bodies) enables us to explore the roleof ice for planetary formation and evolution and the emergence of habitable planets. SPICA surveys
will thus provide the first census of the water ice content towards hundreds of planet forming
systems in our Galaxy. A complementary approach with SPICA/SCI to search for NIR ice
absorption features in the disk scattered light spectra should be accomplished (see e.g., Honda et al.
2009 for water ice coronagraphic observations at ~3.1 μm).
For nearby debris disks (d~10 pc) such as those around Vega, Formalhaut or β Pictoris (~100A-type stars), the angular resolution of SPICA at the 44 μm water ice feature will be sufficient tospatially resolve the location of the snow line (the diffraction limited resolution is ~3'') . In debris
disk, presence of water ice grain is not fully established. There is a prediction that water ice grains
can not survive around early type stars due to photosputtering by UV irradiation (Grigorieva et al.
2007). Therefore, observation of presence/absence of water ice grains around debris disks and its
distribution is important to understand the stability of ice grains. Furthermore, SPICA/SCI MIR
coronographic spectroscopic studies of disk scattered light should also be made because it enables
us high angular resolution spectro-imaging, which is complementary to SPICA/SAFARI
observations, again. SCI high contrast and spectroscopic capabilities will enable to detect MIR
dust/ice spectral features in very faint debris disk and investigate their evolution as a function of
disk radii.

56

Fig.2.4-8 ISO spectrum of the circumstellar disk around HD 142527 young star (adapted from
Malfait et al. 1999) showing the model components including the crystalline water ice FIR features.
Water ice can only be directly detected at these temperatures through the ~44 and ~62μm FIRemission features. SPICA will take the equivalent spectra of objects at flux levels less than 10 mJy
in one minute in SAFARI's low spectral resolution mode.

Objective #5: Survey of Primordial Objects in the Solar System
In order to reveal the whole picture of the solar system, we will survey physicalinformation on primordial objects in the solar system.

Since the discovery of the first Kuiper-Belt object, 1992 QB1 (Jewitt & Luu 1993), our view of thesolar system is undergoing radical changes and has been expanding. One of the goals for the solar
system science in the next decades is the establishment of comprehensive catalogue ofphysicochemical properties for primitive solar system small bodies (SSSBs); near-Earth objects,
main-belt asteroids, Jovian Trojans, Centaurs, trans-Neptunian objects (TNOs), comets, and so on.
Albedos, diameters, and thermal inertias of SSSBs from asteroids to TNOs are particularly
important information for the study on the origin and evolution of the solar system. It is generally
recognized that TNOs are the remnants of planetesimals beyond Neptune’s orbit in the early solar
nebula, which are physicochemically unaltered by the solar radiation. The present distribution of
TNOs shows the sign of the dynamical migration of the giant planets in the early solar nebula(Malhotra 1993; Levison & Morbidelli 2003). It is a hint of the initial mass distribution of the57

planetesimals in the proto-planetary nebula (Morbidelli et al. 2003; Gomes et al. 2005).
It is, however, not easy to derive the albedo and size of TNOs by observations in either
optical (reflected light) or infrared/radio (thermal emission) range alone. The combination of
measurements at optical and infrared/radio range constrain these properties of TNOs. Especially,
multi-band observations of the thermal emission around its peak wavelength are important for thedetermination of the precise SED of TNOs (Stansberry et al. 2008; Brocker et al. 2009).
SPICA/SAFARI-MIRMES will cover the wavelength region of thermal radiation of asteroids andTNOs (30 to 210 μm) and have good sensitivity throughout the infrared. It is also supposed that
surface conditions of TNOs might give us information on the constituent materials that make upplanetesimals. In the far-infrared region, there are diagnostic spectral features of water ice andminerals. Past infrared satellites, and even Herschel, do not have the enough capabilities andsensitivities to detect these features in far-infrared region. SPICA/SAFARI will be the first
instrument to observe these ice and dust features for the brightest TNOs.
SPICA/SAFARI will be able to detect most of the known outer SSSBs and the SSSBs which
will be discovered in the future in the photometric mode, specifically TNOs of 50 km in diameter at
35 AU, and 100 km TNOs at 50 AU (Fig.2.4-9). Herschel will observe the TNOs larger than 250 km,
and requires ~300 hours to detect photometrically ~10% of the currently known TNOs. JWST does
not cover the critical wavelength range longer than 30 micron. In addition, SPICA/SAFARI cancarry out the first far-infrared spectral survey for the brightest TNOs. Therefore, SPICA will
provide the precious information to the correlation between the size and albedo distribution and theorbital properties for TNOs, and clarify the dynamical evolution beyond the giant planet region in
the early solar nebula. With the help of 10 times or more higher sensitivity than AKARI, we will
make an unprecedented survey of the albedo, size, thermal inertia, and surface condition for SSSBs.
Since the confusion limit does not apply for moving objects like TNOs, extremely deep sensitivity(better than 50μJy, 5σ, achieved with SAFARI GOAL detectors) in the far-IR can provide dramatic
improvement in the exploring capability of our solar system, hence highly recommended.
Fig.
2.49
Dia
met
ers
(in
km)
of a
pop
58

ulation of known outer solar system objects as a function of their heliocentric distance, comparedwith the detectability predictions for photometry (left) and spectroscopy (right). SAFARI predictions
do not take into account the confusion limits.

59

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60

3. ミッション要求 Mission Requirements
3.1 科学目標・成功基準からミッション要求の導出 Mission Requirement Breakdown from ScientificTargets and Success Cliteria
2 章で述べた科学目標とフルサクセス成功基準からミッション要求が導かれる過程を図 3.1-1〜3 に示す。

図 3.1-1 科学目標・フルサクセス成功基準からミッション要求が導かれる過程（銀河誕生のドラマ）

61

図 3.1-2 科学目標・フルサクセス成功基準からミッション要求が導かれる過程（物質輪廻の解明）

62

図 3.1-3 科学目標・フルサクセス成功基準からミッション要求が導かれる過程（惑星系のレシピ）
3.2 ミッション要求サマリ Summary of Mission Requirements
ミッション要求は、目標を達成するために必要な要求事項を集約したものである。要求は仕様とは区別され、機能要求として記述する。ただし、観測機器等については技術的な性能要求(「仕様」63

とは異なる)についても記述する。
The mission requirements describes the required instrumental capability to achieve thescientific objectives & targets. Note that the ``Requirements” is different from the``Specifications”, and they are described as functional requirements over variety of technicalaspects.
前節で示したブレークダウンから、フルサクセスレベル（2.1 節）で達成するために必要かつ十分なミッション要求を以下のようにまとめた：•

望遠鏡に対する要求•

口径３ｍクラスの望遠鏡を極低温（６Ｋ以下）に冷却•

精度：波長 5μm での回折限界、波面誤差で 0.35μm 以下•

視野 30 分Φ以上•

光学効率変化：ミッション期間中効率が 10%以上劣化しないこと（ コンタミネーションに関するシステム要求）
•

コア波長：
•

5−210μm

JWST、ALMA では観測できない波長帯

•

観測期間：

•

可視範囲：全天の 20%以上の領域が観測できる visibility を有すること。

•

データ発生量：•

焦点面観測装置•

２年以上
4 M bps（一日分の観測データを蓄積し、地上に伝送できること）

検出感度 : Herschel（波長＞60μm）よりも 1.5 桁以上の分光感度、コンヒュージョン
限界の撮像感度。

•

視野要求：
中間赤外線撮像：4 分角以上 ／•遠赤外線撮像：2 分角以上

波長域・波長分解能要求：
５−２１０ μm （撮像）、２０−２１０μm で低分散・中分散分光機能•

姿勢精度要求波長域・モード

指向制御精度(3σ)

指向安定度(0-P)

中間赤外線撮像

15”

0.075” / 600 sec

中間赤外線(≧20μm)分光

0.625”

0.625” / 600 sec

遠赤外線撮像12”0.15” / 20 min

遠赤外線分光12”0.15” / 20 min

次に FPI オプション機器・機能要求に関しては、以下のようにまとめられる：• オプション観測装置についての機能要求
64

R~100 の低分散、及び 1000 の中分散分光機能（5-20μm）
R~30,000 の高分散分光機能（4-8, 12-18μm）
中間赤外コロナグラフ機能
サブミリ波分光機能
近赤外(0.8-5μm)分光・撮像機能•

オプション観測装置についての姿勢精度要求
波長域・モード

指向制御精度(3σ)

指向安定度(0-P)

中間赤外線高分散分光

0.135”

0.075” / 600 sec

中間赤外線コロナグラフ

0.03”

0.03” / 20 min

以上の要求根拠（特に、前節のブレークダウンでは明示していない観測期間・可視性・データ量、
望遠鏡光学効率）については、3.3 節、3.4 節で詳しく述べる。

3.3 ミッション要求の詳細 Overview & Summary of Mission Requirements
表 3 にミッション要求の詳細を示した。以下にこれらの要求根拠および背景を詳細に述べる。
(ア) 波長領域 Wavelength Coverage
JWST・Herschel・ALMA では困難だが SPICA でこそ行うべき科学目的・目標を２章では詳しく述べた。これらを達成するためには、赤外線、特に中間・遠赤外線での高感度の観測を行なうことが最重要である。そこで、SPICA では、波長 5-210μm の中間・遠赤外線領域をコア波長域と設定する（それより短波長および長波長側はオプション）。JWST と Herschel のカバ
ーしない波長域（20−60μm）では、SPICA のみが感度および解像度で独壇場となる。また、
この波長 20μm―210μm をカバーすることがミッションの成功に必須である。
In section 2, we described the scientific objectives & targets which shall be performed
uniquely with SPICA, while they are quite difficult to be achieved with JWST, Herschel,and ALMA. High sensitivity in the mid-and far-IR is most important. Therefore, the corewavelength of SPICA is defined as 5-210 μm, and shorter or longer wavelength extension is
optional. Namely, wavelengths longer than 20μm, where JWST/MIRI lacks good capability,
are mandatory to be covered with SPICA.
(イ) 望遠鏡の温度 Temperature of the Telescope
波長 5-210μm の中間・遠赤外線領域において、充分な感度を達成しようとする際に留意すべ
き点は、観測機器からの熱放射を、自然背景放射よりも低く抑えることである。これができな
いと、観測機器からの熱放射の揺らぎが観測限界を決めてしまうことになり、本来達成することができる感度にまで到達することができないためである。遠赤外線域で自然背景放射よりも、
65

望遠鏡の熱放射をおさえるためには、望遠鏡を６K 以下に冷却しなければならない（図 3.1-4）。
A key requirement to achieve sufficient sensitivity at 5-210μm is to suppress the thermal
emission from the instrumentation well below the natural background emission. As shownin Fig. 3.1-4, the telescope should be cooled to (or below) 6K to achieve the requirement.

Fig. 3.1-4 : Comparison between
thermalemission

from

the

telescope at various temperature
and

the

naturalbackgroundradiation (zodiacal emission andCirrus(Galactic dust emission).

(ウ) 望遠鏡の口径 Diameter of the Telescope Primary Mirror
望遠鏡の口径に対する要求には、集光力と解像度という 2 つの側面がある。多くの科学目標の達成のためには 3.0m 級以上が必要である（2.5m 未満では、殆どの科学目標の達成が不可能である）。集光力は、天体の検出感度に直接影響する（（エ）で詳述）。解像度要求は、多くのミッション要求において、厳しいものはない（コロナグラフ観測は例外、以下に詳述）。60μm より長波長側では、Herschel の解像度を上回ることはできないが、我々の銀河系内の星間物質や近傍銀河の観測においては、Herschel には不可能な低輝度拡散放射を高精度で測定することがSPICA だけが可能であることを考えると、3m クラスの口径の実現が強く望まれる。
なお解像度要求は、3m 級口径の回折限界をすべてのコア波長域で実現すること、であるので、鏡面精度に対する要求となる。コロナグラフ観測に関してはさらに厳しい鏡面精度要求がある（3.2.3 に詳述）。
There are two aspects in the telescope diameter requirement, the light-collecting power
and the spatial resolving power. In most of scientific targets, 3.0m-class or larger telescopeis necessary. The light-collecting power directly affects the sensitivity, while the spatial
resolving power requirement is not so stringent for most of the science requirements except
for the coronagraph observations. Although Herschel achieved excellent spatial resolving
power at wavelengths beyond 60μm, only SPICA enables us to accurately measure thefaint diffuse emission from the interstellar matter and nearby galaxies with the cooled 3-mclass telescope.
(エ) 感度 Sensitivity
ミッション要求の実現のためには、以下の感度を一時間程度の積分時間（5σ）で達成することが求66

められる。これらを達成するには、FPI の性能も重要だが、望遠鏡の口径（集光力）を約 3m 以上とすることが必要である。
It is desired to achieve the following sensitivities in one hour integration (5σ) or so with
sufficiently high performance of FPI as well as the collecting power of 3m-class telescope.
中間赤外線撮像 MIR imaging（波長 5－40μm）：10μJy at least, 1μJy is favorable
遠赤外線撮像 FIR imaging（波長 40－200 μm）：100μJy @50μm at least, 50μJy is favorable（excluding the confusion limit コンヒュージョン限界は除外した数値）
中間赤外線分光 MIR spectroscopy（波長 5－40μm）：(低分散 low-dispersion)

50μJy at least, 10μJy is favorable(中分散 moderate-dispersion)

Line sensitivity: 10-19W/m2 at least

遠赤外線分光 FIR spectroscopy（波長 40－210 μm）：
(低分散 low-dispersion)

1mJy @50 μm at least, 0.2mJy is favorable(中分散 moderate-dispersion)

Line sensitivity: 10-18W/m2 at least（検出器のピクセルサイズを最適化できるのであれば）望遠鏡の集光力と、天体の検出限界は反比例する。 従って 3.0m の場合、3.5m の時の検出限界は 1/0.73=1.4 倍に悪化する。次に述べるコン
ヒュージョン限界と無関係な撮像・分光観測では、観測時間（検出限界の２乗に比例して増大）が、
ほぼ 3.5m の場合の 2 倍必要となる。
The detection limit for a point-like source is inversely proportional to the light-collecting powerof the telescope (so far as the detector pixel size, i.e. spatial sampling resolution is optimized.
Thus, the detection limit with 3.0m aperture is worse by a factor of 1/0.73=1.4 than that with
3.5m aperture. In case of observations free from the source confusion, roughly twice longer
integration time (i.e. proportional to the square of the detection limit) is necessary for the 3.0m
aperture telescope.

Fig.3.1-5 Expected point-source
sensitivities of SPICA/MIRACLE(green) & SAFARI(red, orange) incase of 3.0m (effective diameter)
telescope. Gray lines are for 3.5m
telescope. Confusion limit by faintgalaxies (Takeuchi et al. in prep.) is
shown by dotted lines. Crosses are
JWST/MIRI expected sensitivities.

(オ) 波長分解能 Wavelength Resolution67

分光観測における波長分解能要求は以下となる。中間赤外では、JWST の分光機能にはない高分散分光機能を持つことが強く望まれる。
中間赤外線分光 MIR spectroscopy（波長 5－40μm）：(低分散 low-dispersion)λ/δλ ~100(中分散 moderate dispersion)λ/δλ ~1000(高分散 high dispersion、λ<20μm)λ/δλ ~30,000 (velocity resolution of 10km/s)

遠赤外線分光 FIR spectroscopy （波長 40－210 μm）：
(低分散)λ/δλ ~100(中分散)λ/δλ ~2000 at 100μm(カ) 視野要求 Field-of-View
撮像・分光観測における視野要求は以下となる。中間赤外線では、JWST よりも十分大きな視野を持ち、掃天観測能力で JWST を圧倒すべきである。遠赤外線においては、低分散分光を行いつつ広い視野を観測する（３次元マッピング）能力をぜひ持つべきである。そのためには、各焦点面観測装置が、以下に掲げる視野を持つ必要がある。さらに、それらの観測装置を搭載するために、望遠鏡のケラレのない視野として、直径 30’φ以上が必要となる。
Field-of-view (FoV) requirements in both imaging and spectroscopy is shown below. In
Mid-IR, sufficiently large FoV than JWST is desired. In the Far-IR, large imaging FoV with
low-dispersion spectroscopic capability (i.e. 3D mapping) is recommended. Hence each
instrument is required to have a FoV listed below. To accommodate the instruments,
30arccmin diameter unvignetted FoV of the telescope is required.
中間赤外線撮像 Mid-IR Imaging (5－40μm) : 5’x5’ minimum, 6’x6’ is favorable
遠赤外線撮像 Far-IR Imaging (40－200 μm): 2’x2’ minimum @40-70 μm deep imaging
中間赤外線分光 Mid-IR spectroscopy (5－40μm):>1’ desirable for low-resolution spectroscopy with multi-slit>10” desirable for moderate-resolution spectroscopy
遠赤外線分光 Far-IR spectroscopy (40－210 μm): 2’x2’ is desirable for fast 3D mapping(キ) 観測期間 Duration of Observations
観測期間（定常運用に移行後、フルサクセスレベルの観測運用を終了するまでの期間）に対する要求は、観測ターゲットの可視性に大きく依存する。天の黄極方向を除き、SPICA が同じ
天体を常に観測できるわけではなく、例えば黄道面方向の天体は、年に 2 か月程度の期間しか可視性がない。また天体によっては（超新星のように）定期的に観測を継続的に行う必要がある。このような理由から、観測期間は２年以上と要求されている。
The duration of observations (defined as a duration between the start and end of routine
observation to achieve the objectives at the full-success level) critically depends on thevisibility of the observation targets. Except for the objects near the ecliptic poles, SPICA
68

cannot observe the same targets at any time. For example, the targets at the ecliptic plane
will be visible over ~2 months from SPICA in a year. For some sources like Supernavae,
periodic observations should be performed. Therefore, observing duration more than two
years are requested.
また、科学コミュニティが掲げる全１６項目の科学目標をフルサクセスレベルで達成するのに必要な実観測時間（天体からの赤外線を実際に SPICA の装置で観測を行っている時間）は、
口径 3.5m を前提とした場合 10−20 日、口径 3.0m の場合 20−40 日と見積もられている。表２，３には合計 16 の科学目標を掲げており、これらの実行には実観測時間で約１年（口径 3.5m）、２年（口径 3.0m）が必要となる。衛星ミッションとしての成功基準 6 項目（表 2.1-2）すべてを満足するには、実観測時間で約９カ月が最低限必要である（口径 2.5m では、ミッション成功基準を達成するためだけの観測を行ったとしても、観測期間のマージンが殆ど確保できない）。
The net observing time (i.e. on-source exposure time with SPICA) to achieve thefull-success level of each scientific target (in Table 2) is estimated to be 10-15 days in caseof 3.5m telescope, while 20-30 days in case of 3.0m. To fulfill all the scientific targets inTable 2 (17 in total), the total net observing time amounts to approx. 1 year (2 year) for
3.5m (3.0m) telescope. In order to perform the Mission Success Cliteria( Table 2.1-2 ) at the
Full-Success level, net observing time of at least 9 months is required. Hence with 2.5m
aperture telescope, we cannot allocate margin in the nominal observing duration of two
years.
(ク) 可視範囲 Visibility
上記に述べられたような限られた観測期間を有効に活用するために、観測期間中はいつでも、全天の 20%以上の領域が観測できる visibility を有すること。
To make the best use of the observation period discussed above, SPICA is required to have avisibility to cover more than 20% of the all sky at any time during the observation period.
(ケ) 運用(時期) Timing of Commissioning of the Mission
遠赤外・サブミリ波においては、Herschel が 2009 年に打ち上げられ、この波長域でこれまでになく高い解像度の観測がおこなわれる。この成果を十分に活かすこと、Herschel でできないことを見極めて SPICA による観測計画を立案すべきである。
また地上ではミリ波サブミリ波干渉計 ALMA が 2011 年頃から観測を開始する予定であるし、（主に近赤外線波長主体の）スペース大望遠鏡 JWST が 2014 年に打ち上げられる。SPICA は、
これらの次世代観測装置と波長域や分光・撮像能力において相補的であり、従って未だ JWST・ALMA が運用を続けている間に観測を開始することが強く望まれる。
また地上光赤外の次期計画として提案されている大型望遠鏡 TMT が、やはり 2018 年頃の実現
69

を目指している。宇宙再電離期の天体の正体を探ること、惑星系形成の総合理解を進める上で、TMT と SPICA のシナジーは非常に重要であり、TMT と同時期の実現が望まれる。
Herschel has been launched in 2009, and undertaking far-infrared imaging with
unprecedentedly high spatial resolving power. For planning the observation with SPICA weshould take into account of the achievement of Herschel.
Atacama Large Millimeter/submillimeter Array (ALMA) will also start observations fromaround 2011, and JWST will be launched in 2014. SPICA is complimentary to these next
generation facilities in respect of wavelength coverage and spectral/imaging capabilities,
and thus early commissioning of SPICA is very much recommended.
Thirty Meter Telescope (TMT), a next generation telescope for the ground optical/IR
astronomy, is also planned to start commissioning in 2018. In order to reveal the nature ofsources responsible for the Cosmic re-ionization, and to thoroughly understand theplanetary system formation, synergy between TMT and SPICA is quite important, and thus
SPICA should be realized in the similar timing of TMT commissioning.
(コ) データ量 Data Volume and Rate
上記の視野を持つ観測機器を効率的に運用するためには、4Mbps 以上のデータ発生量に対して、それを一日分以上の観測データ蓄積し、地球に適切に伝送する能力を有することが求められる。
To operate the instruments with the FoV listed above, SPICA is required to be able to store
the data for at least a day and send the data with the data rate of 4Mbps.

(サ) 望遠鏡の光学効率変化 effective transmittance of the telescope
上記で議論された感度をミッション中に維持するために、望遠鏡の光学効率がミッション期間中
で 10%以上は変化しないよう、コンタミネーションが低く抑えられなければならない。
To keep the sensitivity during the mission, contamination of the telescope is required to keep
low so that the effective transmittance of the telescope does not change more than 10%
during the mission period.
(シ) 観測装置 Observing Instruments
2 章で述べた３つの科学目的大項目のすべてに用いられている観測装置は、MIRACLE、
MIRMES、SAFARI の３つである。MIRHES は、「惑星系形成」の科学目標（表 2 および表 3の第 1、第 2、第 3）と、「物質輪廻」の科学目標（第 3）の達成のために用いられている。
SCI、BLISS は、それぞれ「惑星系形成」（第 1、第 4）、「銀河進化」（第 1、第 2、第 3）のエ
クストラな成功基準達成のために用いられている。FPC-S も「銀河進化」（第 1、第 2）及び「物質輪廻」の第４、6 目標のエクストラな成功基準を達成するために必要である。
Three focal plane instruments, MIRACLE, MIRMES, SAFARI, are utilized to perform all70

major scientific objectives. MIRHES is utilized to perform objectives in the planetary systemformation (#1, #2, & #3) and the life cycle of interstellar matter (#3). SCI is utilized toperform the extra success of the planetary system formation (#1, #4), while BLISS is utilized
to perform the extra success of the evolution of galaxies (#1, #2, & #3). FPC-S is also
necessary to perform the extra success of the evolution of galaxies (#1 & #2) and thelife-cycle of interstellar matter(#4, & #6).
(ス) 指向精度および安定度 Pointing accuracy and stability
ミッション要求から各観測モード毎に整理された観測指向精度要求および運用要求を本節にまとめる。精度要求は各々クロススリット方向とアロングスリット方向で異なり、要求異方性を持つ。以下、特に断りのない限り、より厳しいクロススリット方向の数値を示す。また N/A とは、その FPI の該当するモードにおいて非適用(Not Applicable)であることを示す。TBD 項目は具体的な数値が確定していないが、基本的に AKARI と同等性能を要求されることを前提とする。
The pointing accuracy and stability requirements for each observing mode are summarized
as follows. The accuracy requirements is different between cross and along the slit directions.
In the following values refer to those for the along-the-slit direction (more stringent).
ポインティングモードにおける指向精度要求 Pointing Mode
各観測モードのポインティングモードにおいて要求される指向精度要求を表 3.1-1 に示す。これらの要求に対して、単一周波数から構成される指向誤差を想定し周波数に応じた指向精度要求を表現したものを図 3.1-6 に示す。もっとも厳しい要求を赤太字で示す。

表 3.1-1 ポインティングモード指向精度要求
Table 3.1-1 accuracy/stability requirements in the pointing mode
Absolute pointing control
Pointing stability
Observation mode
accuracy [arcsec] (3σ)[arcsec, 0-P] /time (3σ)
MIRACLE Imaging Short
15
0.075 / 600[sec]
MIRACLE Imaging Long
15
0.21 / 600[sec]
MIRACLE Spectroscopic Short
0.135
0.135 / 600[sec]
MIRACLE Spectroscopic Long
0.405
0.405 / 600[sec]MIRHES (S-mode) 0.72 x3.5
0.216
0.216 / 600[sec]MIRHES (L-mode) 1.2 x6.0
0.36
0.36 / 600[sec]MIRMES (Arm-Short) 12 x6
0.3
0.3 / 600[sec]MIRMES (Arm-Long) 12 x12.5
0.625
0.625 / 600[sec]SAFARI (SPECObserve Mode)
120.15 / 20[min]SAFARI (PHTObserve Mode)
120.15 / 20[min]FPC-S Imaging mode
0.3
0.1 / 600[sec]
BLISS dispersion
0.5
0.5 / 1[hour]
Coronagraph0.03 (0-P)
0.03 / 20[min]71SPICA Pointing Accuracy Requirement

1E+2

Angle [arcsec]

1E+1

MIRACLE imaging-mode
MIRACLE spectroscopic-mode
MIRHES (S/L-mode)
MIRMES (Arm-Short/Long)SAFARI (SPECObserve Mode)
SAFARI (PHTObserve Mode)
BLISS dispersion
FPC-S imaging-mode
Coronagraph

SAFARI

1E0

1E-1

MIRACLE spectroscopic
MIRACLE imaging
Coronagraph

1E-2
1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E0

1E+1

1E+2

1E+3

Frequency [Hz]図 3.1-6 ポインティングモード指向精度要求 (周波数領域表示)
Fig. 3.1-6 Pointing accuracy requirements in the frequency domain
指向決定精度要求

Attitude Determination Accuracy

ポインティングリコンストラクション後に達成すべき指向決定精度である。SAFARI、BLISS 等、
陽に指向決定精度を要求する FPI を表に示す。他の FPI の決定精度は制御精度と同等レベルを達成要求とする (決定精度が制御精度より悪くなることは定義上ありえない)。
表 3.1-2 指向決定精度要求
Table 3.1-2 Attitude determination accuracy
Observation mode
Pointing determination accuracy [arcsec] (3σ)(After pointing reconstruction)
SAFARI
0.15
BLISS
0.5
ステップスキャンモードにおける指向精度要求

Step-scan mode

各観測モードにおけるステップ運用モードに対する指向精度要求を表に示す。ステップ方向は、
衛星機体 X 軸回り／Y 軸回りあるいはその合成軸回りであり、Z 軸回りのステップ運用は、冷却系が要求する太陽角制限に基づき実施しないことを基本とする。
Requirements in the step-scan mode are shown in Table 3.1-3. Direction of a step is around
X or Y-axis, or mixture of both axis of the spacecraft, while no step-scan around the Z-axis ispermitted due to the Sun-avoidance angle constraint.
72表 3.1-3 ステップスキャンモード指向精度要求
Table 3.1.3 Requirements in the step-scan mode
Step angle
Step angle
Observation mode
[arcsec]
accuracy[arcsec]
MIRACLE Imaging dithering
0.075~22.8
0.075~0.39
MIRACLE Spectroscopic Step Scanning
0.135~1.14
0.135~0.57

Settling time
[sec]
30
30

MIRHES (S-mode) Single Staring

1.17 (along slit)

0.216

MIRHES (L-mode) Single Staring

2.0 (along slit)

0.36

AKARI Performance
Level
AKARI Performance
Level

0.216

AKARI Performance
Level

0.36

AKARI Performance
Level

0.3

AKARI Performance
Level

0.625

AKARI Performance
Level

0.3

AKARI Performance
Level

0.625

AKARI PerformanceLevel

0.1 (3σ)±12 (overlap)±12 (overlap)
N/A
N/A

N/A
100
100
N/A
N/A

MIRHES (S-mode) Step Mapping
MIRHES (L-mode) Step Mapping
MIRMES (Arm-Short) Single Staring
MIRMES (Arm-Long) Single Staring
MIRMES (Arm-Short) Step-Mapping
MIRMES (Arm-Long) Step-Mapping
FPC-S Step scan mode
SAFARI （SPECObserve Mode）
SAFARI（PHTObserve Mode）
BLISS
Coronagraph0.36 or 0.72
(cross slit)
2.9 (along slit)
0.60 or 1.20
(cross slit)
5.0 (along slit)
0.60 (cross slit)
6 (along slit)
1.25 (cross slit)
6 (along slit)
4.8 (cross slit)
10 (along slit)
10 (cross slit)
10 (along slit)
3
108
108
N/A
N/A

彗星追尾モードにおける指向精度要求 Non-siderial tracking mode
各観測モードにおける彗星追尾モードに対する指向精度要求を表 3.1-4 に示す。彗星追尾モードを有しない観測モードを除き、基本的に指向精度要求はポインティングモードにおける指向精度要求と同等である。コロナグラフ観測装置の同モードは現状 N/A である。
表 3.1-4 彗星追尾モードにおける指向精度要求
Table 3.1.4 Requirements in the Non-siderial tracking mode
Items
Requirement
Pointing accuracy / stability
Same accuracy / stability as pointing mode
Tracking speed< 10 arcsec/min
Tracking duration< 1200 sec
スロースキャンモードにおける指向精度要求 Slow-scan mode
各観測モードにおけるスロースキャンに対する指向精度要求を表 3.1-5 に示す。スキャン速度×
スキャン継続時間が FPC-G の視野範囲を超える場合には別途性能を規定する。SAFARI に関しては、FPC-G は本モードで用いないことを前提とする。
表 3.1-5 スロースキャンモード指向精度要求73

Table 3.1-5 Slow-scan mode requirements
Scan speed
Scan speed
range
accuracy
Observation mode
[arcsec/sec][arcsec/sec]
MIRACLE Spectroscopic Slow scan
0.054~2.28
10 %MIRHES (S-mode)
N/A
N/A
MIRHES (L-mode)
N/A
N/A
MIRMES
N/A
N/A
FPC-S Slow scan mode
TBD
TBD
SAFARI （SPECObserve Mode）
N/A
N/A
SAFARI（PHTObserve Mode）
10~72
1%
BLISS (A2-D rastered mapping mode)
1~20
1% *1
Coronagraph
N/A
N/A
*1
20arcsec/s で 10arcmin スキャン時

Scan
duration
[sec]
>5~50
N/A
N/A
N/A
TBD
N/A
600
600 *1
N/A（参考：用語の定義）
指向精度

指向軸を観測対象方向に指向させる際の精度として定義する。具体的には、観測要求に応じて、絶対指向制御精度および指向安定度の規定がある。指向精度という場合には、これらの総称を表す概念として扱う。
絶対指向制御精度観測対象を検出器の所定の位置に入れることを目的として、指向軸を観測対象方向に指向させる際の制御精度として、3σの統計量として定義する。指向制御精度は、搭載系で実現すべき精度である。指向制御精度には、その誤差要因として、アライメント誤差（あるいは、アライメント
補正誤差）、姿勢制御誤差（あるいは指向軸制御誤差）、姿勢制御（あるいは指向軸制御）で制御できな
い内部擾乱による誤差を含む。
指向安定度

規定時間における検出器上の観測対象の移動量をある所定の値以下に抑えることを目的として、指向させるべき軸を観測対象方向に指向させる際の安定度として 3σの統計量として定義する。 0-P は

P-P の 2 分の 1 の意である。指向制御精度が時間的に一定である固定成分を含めて規定されるのに対して、指向安定度はこの成分を含まず、ある規定時間における変動成分のみで規定する。
指向安定度は、搭載系で実現すべき精度である。指向安定度には、その誤差要因として、規定時間内に変動するアライメント安定度、姿勢制御安定度（あるいは指向軸制御安定度）、姿勢制御（あるいは指向軸制御）では制御できない内部擾乱誤差を含む。
3.4 科学目的別特記事項 Special topics for each Scientific Objectives
3.4.1. 銀河の誕生と進化過程の解明 Resolution of Birth and Evolution of Galaxies
望遠鏡口径：口径は、高赤方偏移宇宙の探査（目標第 1）にとって最も重要である。図 3.2-1 は、宇宙赤外線背景放射を、一個一個の銀河に分解する能力を、口径の関数として示したものである。宇宙赤外線背景放射の 50％を波長 160 で分解するためには、少なくとも 3m の口径が必要である。さらに、銀74

河コンヒュージョンによる限界は、特に中間赤外線波長で口径に大きく依存する（図 3.2-2）。
The requirement on diameter of telescope is most serious for probing high-z universe (Objective #1).
The best sensitivity is required for detecting distant, faint galaxies, hence the required observing
time is inversely proportional to the effective collecting area of the telescope primary (common to all
the objectives #1~#5). Figure 3.2-1 shows the capability of resolving CIRB as a function of telescope
diameter. In order to resolve 50% of CIRB at 160μm, we need 3-m diameter at least. More
importantly, however, the sensitivity limit due to the galaxy confusion is more stringent in the
mid-infrared rather than far-infrared: showing strong dependence on the telescope diameter(Figure 3.2-2).

Fig. 3.2-1: Resolving capability of
Cosmic Infrared Background (CIB)
to discrete sources(galaxies) as afunction of telescope diameter(Dole, 2004).

Fig. 3.2-2: sensitivity degradation
factor (with respect to 3.5m) for
the galaxy confusion limit(Takeuchi et al. in prep.).

波長域・検出感度・観測装置：

オプション装置の BLISS は、波長域・検出感度の面で SAFARI と相補的な装置であり、その実現は科学目標の達成のために強く望まれる。例えば、目標第 3 ( Metallicity
Evolution )で重要な役割を担う[C II] 158μm、[N II] 205μm 等のスペクトル線は、SAFARI では赤方偏移のために、我々が最も関心のある遠方宇宙の銀河からは観測することができない。
Wavelength Coverage / Sensitivity of BLISS (optional instrument) is complementary to those of
SAFARI, and thus its realization is very much desired to achieve the extragalactic scientific targets.
For example, the fine-structure lines such as [C II] 158μm, [N II] 205μm are known to play animportant role to achieve the Objective #3 (Metallicity Evolution) from distant Universe cannot be
75

observed with SAFARI due to the redshift.
3.4.2 銀河星間空間における物質輪廻の解明 The Transmigration of Dust in the Universe
観測装置の視野：近傍銀河や銀河系内星間塵雲の研究においては、天体は空間的に広がっており、波長によって変わらない固定された大きさの視野からの放射の、多波長分光スペクトル情報を取得することが強くのぞまれる。さらに、星などの点源のまわりのコンパクトな放射領域（〜10 数秒程度）の空間情報を得ることが非常に重要である。
観測期間要求：超新星観測（目標＃１）においては、最低１年にわたる時間的な変化を追うことが本質的である。このため、ミッション観測期間として２年以上継続することがのぞまれる。
望遠鏡口径：望遠鏡の口径縮小により観測限界が悪化することのサイエンスへの影響は、多くの科学目
標に関して問題とならない（２ｍ級でも実施可能なものもある）。しかし、遠赤外線波長域では口径３．
５ｍの Herschel がすでに観測を開始していることを考えると、解像度を著しく落すことは避けなければならない。この点で３ｍクラスの実現が強く望まれる。
Field-of-View Requirement: in the study of interstellar matter of nearby galaxies and Galacticinterstellar dust clouds, multi-wavelength spectra of the extended emission from the fixed-size FoV
common to all the wavelength is strongly desired, in order to avoid the uncertainty from the spatial
extension which may vary with wavelength. Furthermore, it is very important to obtain “compact”
spatial information (~10 and a few arcsec scale) around the energy sources (such as stars).
Duration of Observation: as for the SNe observations (target #1), it is essential to follow the time
variation. Thus it is strongly desired to have more than two years duration for the routine
observation phase.
Diameter of Telescope: the impact of sensitivity degradation due to the shrink of the telescope
diameter is moderate (even 2m-class, some mission objectives can be achieved), however, in the
point of view of spatial resolving power, 3-m class aperture is highly recommended since HerschelSpace Observatory (3.5m aperture) is already in space for far-IR and submm observations.
3.4.3 惑星系形成過程の総合理解 Thorough Understanding of Planetary System Formation
コロナグラフによる惑星探査： この観測は、検出限界が鏡面反射率の一様性や表面精度に非常に大きく左右される。また、木星や土星と同様の軌道サイズの惑星系を探査するために、短い波長の観測が特に重要となる。ＪＷＳＴなどとの競合を考慮に入れると、他の観測装置やプロジェクトに比べ厳しい下記の仕様を達成する必要がある。
―

鏡面反射率一様性< 1.5 % rms―

副鏡支持スパイダー

最小限に抑える必要がある。（優先順位：２本＞４本＞３本）

―

観測波長

ミッション全体では最短観測波長は 5 μm となっているが、できる限り
3.5 μm までカバーし、4 μm 付近の惑星固有の分光フィーチャーを検出することが望ましい。
76―

鏡面表面精度装置内の可変鏡により高い精度が達成されるものの、望遠鏡による波面誤差が 2 μm 以内に収められる必要がある。

Coronagraphy of Exoplanets: The detection limit of the space coronagraphy is determined by the
uniformity of the telescope transmission, and surface accuracy of the mirrors. Furthermore, theobservations of short (~5 μm) is highly desired to observe exoplanets with orbital scales similar to
Jupiter and Saturn in our solar system. These impose the most stringent requirements described
below:―

Uniformity of Transmission< 1.5 % rms―

Telescope Spider

should be minimized (the number = 2,4,3 in order ofpreference)―

Wavelength

while the SPICA mission is mainly designed forwavelengths longer than 5 μm, observations at > 3.5 μm is
desired to observe a feature predicted for exoplanets at 4 μm.

―

Wavefront peak-to-valley error

should be compensated using its own wavelengthcompensation, but should be no higher than 2 μm with thetelescope optics.
他のプロジェクト（１）検出器読みだし速度およびデータ量： 惑星のトランジット分光は、距離 = 3- 5 pc 程度の晩期 M 型星（10μｍで 4 - 5 等）がターゲットとなる。その場合、低分散分光でも１秒程度で光電荷が飽和するため、高速読み出しが必要となる。サイエンスの面から必要な時間分解能は１０分のオーダーのため、データ転送量軽減のためデータをまずオンボードで足し合わせ、地上転送する必要がある。
Other Project (1) detector reading and transfer rate: Spectroscopy of transiting planets will target
late M stars at 3-5 pc (4-5 mag.@10μｍ). Since the targets are very bright, this project requires fast
reading (<1 sec). The data corresponding to ~10 min. (i.e., integration acceptable for the sciencegoal) should thus be stuck at the telescope before transferring to the ground in order to achieve a
feasible data transfer rate.
他のプロジェクト（２）コンフュージョン：

3.2.1 節に記述されたコンフュージョンの問題は、遠赤外域でのデブリ円盤の探査に影響する(#3)。口径に対する検出限界の依存性は中間赤外ほどではないものの、より大口径での観測が望ましい。
なお、太陽系内小天体についても遠赤外域での撮像を行うが、他の多くの観測と異なり天体自身が運動するため、複数回の観測によりコンフュージョンノイズを軽減ことができる。
Other Project (2): Source Confusion: The source confusion described in 3.2.1 affects the detection
limit to search for debris disks in the far infrared (#3). The dependence of the detection limit on thetelescope diameter is less crucial than some extragalactic projects, due to observing wavelengths,
though a larger diameter is preferred to achieve the science goal.
77

Note that the FIR observations of solar system small bodies is not affected by the source confusion.
Since these are moving targets, we would be able to minimize the confusion noise due to different
exposures at multiple epochs.

78

4. トレーザビリティ、根拠資料 Traceability Documents
SPICA ミッション要求の提示履歴 Presentation Log to Stake-holders

4.1.

ミッション要求は SPICA を取り巻くステークホルダーと共有されている事が重要である。ステーク
ホルダーの意見・期待・ニーズが的確にミッション要求書に取り入れられていることを示すため、「何時」「誰から」「どの様に」提示されたかの履歴を表 4-1 に記録として記す。
表 4-1 SPICA ミッション要求の提示履歴
提示時期
MDR

説明者
次期赤外線天文衛星ワー

対象

提示資料

宇宙理学委員会

SPICA ミッション提案書(第 2 版)

JAXA 経営者

プロジェクト準備審査説明資料

キンググループ

プロジェクト

宇宙科学研究本部(ミッション提案書からの抜粋)

準備審査
概念設計

SPICA プリプロ

JAXA DE 組織

キックオフ

ジェクトチーム

JAXA SE 部門

概念設計フェー

光赤天連 SPICA タスク

光学赤外線天文連絡ズ

フォース＆SPICA プリ

会・日本天文学会

ミッション要求書 NC 版

ミッション要求書Ａ版ドラフト

プロジェクトチーム

4.2.

SPICA 関連の政策文書（抜粋）Related Political Documents●我が国における宇宙開発利用の基本戦略（平成１６年９月９日

総合科学技術会議）

２．宇宙開発利用の意義、目標及び方針（１）意義③地球・人類の持続的発展と国の矜持への貢献
宇宙開発利用は、長期的視点から地球システムの持続的発展を目指すため、地球環境の現状と人類活動の及ぼす影響を全地球的規模で把握するために、もっとも有効な手段である。また、フロンティ
アとしての宇宙への挑戦を続けることは、国民に夢と希望を与えるとともに、国際社会における我が国の品格と地位を高めることにも大きく貢献する。
（２）目標③知の創造と人類の持続的発展
多くの人々に夢や希望を与えるべく、未知のフロンティアとしての宇宙に挑む。宇宙空間を探査し、利用することにより、宇宙の起源、地球の諸現象などに関する根源的な知識・知見を獲得する。さら79

に、地球の有限性が語られるようになった今日、宇宙からの視点を活用して、人類の活動と地球環境との共生を目ざすとともに、更なる飛躍を求めて、宇宙における人類活動の場を拡大する。
（３）方針
我が国の国際的地位、存立基盤を確保するため、諸外国における宇宙開発利用の状況を踏まえつつ、
我が国は人工衛星と宇宙輸送システムを必要な時に、独自に宇宙空間に打ち上げる能力を将来にわたって維持することを、我が国の宇宙開発利用の基本方針とする。
そのため、技術の維持・開発においては、信頼性の確保を最重視する。また、重要技術の自律性を高めるため、適切な選択と重点化を行った上で、ソフト面も含めた基盤的技術を強化するとともに、技術開発能力を維持する。
なお、研究開発目標の設定や研究開発計画の策定に関しては、利用者の要求を十分に反映することが可能となる仕組みを構築する。
４．分野別推進戦略（３）宇宙科学研究
宇宙科学研究は、真理の追究、知の創造に寄与し、多くの人に夢、誇り及び活力を与えるものであり、宇宙開発利用の柱の一つである。
我が国の独自性を重視した研究開発を推進し、国際的水準の活動を持続する。我が国として独自性を発揮できる、太陽系探査や天文観測などの分野を中心に、資源を集中する。また、国際協力の重要性に配慮した上で、我が国の独自性を発揮できる戦略をとる。欧米などの当該分野の取組みに対しては、その状況を十分踏まえた上で、競争、連携あるいは補完の形をとる。対象分野の選択に当たっては、関連コミュニティの合意と適切な外部評価（他分野の関係者も含める）の下に、透明性を持って実施する。
（６）長期的視野に立つ研究開発の方向性③宇宙科学研究の目指すべき方向
我が国の独自性を打ち出せる、特色ある太陽系探査や天文観測などを推進する。その際には、宇宙物理学や惑星物理学などの基礎科学研究の目指すべき長期的方向性を十分に勘案しつつ、我が国における宇宙科学研究として、知の創造に貢献できる分野に焦点を合わせる必要がある。
●宇宙開発に関する長期的な計画（平成２０年２月２２日

総務大臣、文部科学大臣）

１．我が国の宇宙開発に関する基本的な考え方（１）我が国の宇宙開発の目的
宇宙開発利用を取り巻く国内外の情勢を踏まえ、中長期的な展望に基づく我が国の宇宙政策を策定するに当たり、これまでの我が国の宇宙政策との整合にも配慮しつつ、我が国が宇宙開発を進める目
的と意義を以下のとおり位置付け、我が国の宇宙開発のよって立つべき柱とする。
80◯

我が国は以下の目的の下に宇宙開発を行うものとする。
①

国及び国民の安全と安心の確保②

宇宙空間を活用した社会基盤の整備・拡充③

未知のフロンティアたる宇宙への挑戦（中略）「未知のフロンティアたる宇宙への挑戦」の下では、先進的な宇宙科学ミッションや魅力的かつ先駆的な宇宙探査等のミッションに挑戦し、人類全体の知的欲求に応えるとともに、我が国の宇宙開発活動を支える技術へ成長する可能性を秘めた革新的・萌芽的な技術の創出を目指す。
また、これらの目的に応じた便益や成果を目指すことは、以下のような国として希求する意義に大きく寄与する。
ア）人類の知的資産の拡大・深化
宇宙科学は、人類の知的資産形成に極めて重要な分野である。このため、宇宙科学への積極的な取組は、我が国が人類の知的資産の蓄積に積極的に寄与するという意志を国民と国際社会に明示することとなる。また、宇宙科学研究の推進や宇宙開発の成果に端を発する技術革新の促進は、我が国における知的活動を活性化することにつながるものである。
２．宇宙開発利用の戦略的推進（２）宇宙科学研究の推進
宇宙科学研究は、「宇宙がどのように成立し、どのような法則によって支配されているのか」を知るための高度な知的活動であるとともに、宇宙開発に新しい芽をもたらす可能性を秘めた革新的・萌芽的な技術の源泉であり、宇宙開発利用の基盤を支えるものとして、我が国の宇宙開発利用の持続的発展のために不可欠なものである。また、我が国は、これまでにＸ線天文学や太陽・地球磁気圏観測などにおいて、高い創造性・先導性を有する世界第一線級の成果を上げてきている。
このため、以下の方針により、宇宙科学研究を推進することとする。

◯

長期的な展望に基づき、我が国の特長を活かした独創的かつ先端的な宇宙科学研究を推進する。

国内外の関係する研究者グループとの密接な連携の下、研究者の自由な発想に基づく研究計画から
ピア・レビューを通じて精選し、我が国の特長を活かして、科学衛星の打上げ・運用や理学的・工学的研究など独創的かつ先端的な宇宙科学研究を継続的に実施し、世界最高水準の成果の創出を目指す。
今後重点を置く研究分野は、世界において広く認められる重要な科学目標を有していること、目標及び実現手段における高い独創性と技術及び予算の観点から高い実現可能性を有していること、我が国の独自性と特徴が明確であること、並びに我が国が既に世界第一級にある分野をのばすとともに、これからを担う新しい学問分野を開拓することにも留意することの観点から、以下のとおりとし、ミ81

ッションに即した多様な規模の計画を展開する。
ア）宇宙空間からの宇宙物理学及び天文学地上で実施できない観測を宇宙から行うことにより、宇宙の大規模構造から惑星系に至る宇宙の構造と成り立ちを解明するとともに、暗黒物質・暗黒エネルギーを探求し、宇宙の極限状態と非熱的エネルギー宇宙を探る。
イ）太陽系探査による科学研究
太陽、地球、惑星、始原天体及び太陽系空間環境を多様な手段で調査し、太陽系諸天体の構造、
起源と進化、惑星環境の変遷、これらを通じた宇宙に共通な物理プロセスを探るとともに、太陽系惑星における生命発生、存続の可能性及びその条件を解明する。

●宇宙科学研究の推進について（報告）（平成１８年１２月２１日

宇宙開発委員会計画部会
宇宙科学ワーキンググループ）

第２章

宇宙科学研究における長期的な展望

３．今後のプロジェクト研究の重点分野について（２）各重点分野のプロジェクト研究の目標①宇宙空間からの宇宙物理学及び天文学
1)宇宙の大規模構造とその成り立ちを解明し、暗黒物質・暗黒エネルギーを探る。
ア．長期的な目標
我が国が優位性を持つ赤外線、Ｘ線、ガンマ線及び電波を用いた宇宙観測により、宇宙の大規模構造の姿を捉え、基本的物質であるバリオンや様々なエネルギーの宇宙における存在形態を探ることにより、宇宙の基本構造を解明する。宇宙の初期揺らぎから現在の宇宙の大規模構造に至るまでの過程を解明し、暗黒物質の果たす役割、暗黒エネルギーと宇宙の状態及び進化との関係を探る。
イ．今後５年程度の目標
赤外線天文衛星「あかり」による全天サーベイにより宇宙地図を作成し、銀河進化の解明に資する。Ｘ線天文衛星「すざく」による銀河団等の観測研究を発展させるとともに、大気球や小型衛星等による萌芽的なミッションの開拓を行う。
ウ．２０年先を視野に入れた今後１０年程度の目標
軟Ｘ線精密撮像分光観測による熱的な宇宙の詳細観測を実現する。銀河の誕生過程及び銀河団の進化を解明するために、高解像度赤外線観測衛星及び大型Ｘ線望遠鏡衛星等の大型国際ミッシ
ョンを推進する。銀河構造を解明することを目的とした高精度位置天文観測衛星の実現に必要な技術開発を行う。

82

2)太陽系外惑星の直接観測により惑星の形成過程を探る。
ア．長期的な目標
太陽系外惑星の直接観測により、惑星の形成過程を解明するとともに、生命が存続する可能性のある惑星を探る。
イ．今後５年程度の目標
赤外線天文衛星「あかり」により、惑星誕生環境を探る。太陽系外惑星の直接観測を目的とした次世代高解像度赤外観測衛星の実現に必要な技術開発を行う。
ウ．２０年先を視野に入れた今後１０年程度の目標
次世代高解像度赤外線観測衛星により木星型系外惑星の直接観測を実現する。地球型系外惑星の観測に必要な研究開発を行う。

●衛星の信頼性を向上するための今後の対策について（平成１７年３月１８日
３．調査審議の結果

宇宙開発委員会

推進部会）（１）ＪＡＸＡの衛星開発に関する基本的な考え方

ⅰ）目的を明確に区別した衛星開発の徹底
・今後の衛星開発においては、実利用の技術実証を主目的とするものと、技術開発自体や科学を目的とするものを峻別して、その衛星の開発計画を企画立案する。
ⅱ）目的に応じた衛星の開発②技術開発や科学を目的とした衛星の開発
・科学衛星については、世界初を目指す挑戦的な取組みに合った、衛星の開発を行う。
・技術開発や科学を目的とした衛星の開発においても、信頼性の確保に十分配慮する必要があり、これらの衛星のバスの開発についても、その目的を達成するために必要な技術開発を行う部分以外は、既存技術をできる限り活用するとともに、新規技術を採用する際には、地上試験や解析等
によって信頼性を確保する。
ⅲ）開発期間の短縮
・先ず、予備設計の前（研究の段階）に十分な資源を投入するとともに、計画の企画立案時には、プロジェクトの目標を明確にした適切な開発計画を立て、プロジェクト全体の技術的な実現可能性についての検討及び審査を徹底的に行うことが必要である。予備設計を開始する時点では、既に重要な開発要素は概ね完了し、その他の要素についてもその後の開発研究及び開発の段階で解決すべき課題とその解決方法が見通せていることが必要である。
・今後の衛星の開発期間（予備設計が開始され、開発が終了するまでの期間）を、計画段階において５年程度以内を目途とし、その実現を図っていく。ただし、信頼性を一層向上する等の観点から、
真に止むを得ない場合にあっては、宇宙開発委員会における計画の事前評価の段階でその必要性を十分に吟味の上、この期間を超えることもあり得る。
83

●宇宙基本計画〜日本の英知が宇宙を動かす〜（平成２１年６月２日

宇宙開発戦略本部決定）

別紙２「９つの主なニーズに対応した５年間の人工衛星等の開発計画（10 年程度を視野）」●2010 年

日本学術会議記録

日本学術会議物理学委員会「天文学・宇宙物理学の展望と長期計画」
天文学・宇宙物理学分科会

天文学・宇宙物理学長期計画小委員会 (委員長

佐藤勝彦) 要旨

本小委員会は 天文学・宇宙物理学分野コミュニティーを代表して我が国の天文学・宇宙物理学分野の10〜20 年を見通す展望と長期計画のとりまとめを進め、その中でも次の三つの大型計画は特に日本のコミュニティー全体が一丸となって早急に実現すべき計画である。
・重力波観測計画 LCGT
・次期大型光学赤外線望遠鏡計画 TMT・衛星搭載次世代赤外線望遠鏡計画 SPICA●独立行政法人宇宙航空研究開発機構が達成すべき業務運営に関する目標（中期目標）（平成２０年４月１日

総務大臣、文部科学大臣）

Ⅱ．国民に対して提供するサービスその他の業務の質の向上に関する事項
84２．宇宙科学研究
人類の知的資産及び我が国の宇宙開発利用に新しい芽をもたらす可能性を秘めた革新的・萌芽的な技術の形成を目的とし、宇宙空間からの宇宙物理学及び天文学、太陽系探査、宇宙環境利用並びに工学の分野において、長期的な展望に基づき、我が国の特長を活かした独創的かつ先端的な宇宙科学研
究を推進し、世界的な研究成果をあげる。
（１）大学共同利用システムを基本とした学術研究
宇宙科学研究における世界的な拠点として、研究者の自主性の尊重、新たな重要学問分野の開拓等の学術研究の特性にかんがみつつ、大学共同利用システム※を基本として、宇宙の大規模構造から惑星系に至る宇宙の構造と成り立ちを解明するとともに、暗黒物質・暗黒エネルギーを探求し、宇宙の極限状態と非熱的エネルギー宇宙を探る宇宙空間からの宇宙物理学及び天文学、太陽系諸天体の構造、起源と進化、惑星環境の変遷、これらを通じた宇宙の共通な物理プロセス等を探るとともに、太陽系惑星における生命発生、存続の可能性及びその条件を解明する太陽系探査、
生命科学分野における生命現象の普遍的な原理の解明、物質科学及び凝縮系科学分野における重力に起因する現象の解明等を目指す宇宙環境利用、
宇宙開発利用に新しい芽をもたらし、自在な科学観測・探査活動を可能とするための工学の各分野に重点を置いて研究を実施し、人類の英知を深めるに資する世界的な研究成果を学術論文や学会発表等の場を通じて提供する。
※

大学共同利用機関法人における運営の在り方を参考にし、大学・研究所等の研究者の参画を広く求め、関係研究者の総意の下にプロジェクト等を進めるシステム（２）宇宙科学研究プロジェクト
大学共同利用システム等を通じて国内外の研究者と連携し、学問的な展望に基づいて科学衛星、国際宇宙ステーション（ISS）搭載装置及び小型飛翔体等を研究開発・運用することにより、（１）に掲
げた宇宙空間からの宇宙物理学及び天文学、太陽系探査、宇宙環境利用並びに工学の各分野に重点を置きつつ、大学共同利用システムによって選定されたプロジェクトを通じて、我が国の独自性と特徴を活かした世界一級の研究成果の創出及びこれからを担う新しい学問分野の開拓に貢献するデータを創出・提供する。その際、宇宙探査プロジェクトの機会も有効に活用する。

85

貢献者リスト

List of Contributors

光赤天連 SPICA タスクフォース
SPICA task force for Group of Optical and Infrared Astronomers
市川隆（東北大学・委員長）、泉浦秀行（国立天文台）、今西昌俊（国立天文台）、
川良公明（東京大）、河野孝太郎（東京大）、斎藤智樹（IPMU）、高見道弘（ASIAA）、田村元秀（国立天文台）、山下卓也（国立天文台）、渡部潤一（国立天文台）
Takashi Ichikawa, Hideyuki Izumiura, Masatoshi Imanishi, Kimiaki Kawara, Kotaro Kohno,
Tomoki Saito, Michihiro Takami, Motohide Tamura, Takuya Yamashita, Jun-ichi Watanabe

サイエンスワーキンググループメンバー
Member of Science Working Group
江上栄一（アリゾナ大）、長尾透（愛媛大）、小山祐世（東京大）、山田亨（東北大）、児玉忠泰（国立天文台）、本田充彦（神奈川大）、岡本美子（茨木大）、大坪貴文(ISAS, JAXA)、長谷川直（JSpec, JAXA）、
芝井広（大阪大）、大山陽一（ASIAA）、後藤友嗣（Univ. Hawaii）、鈴木 仁研（国立天文台）、深川
美里（大阪大）、石原大助（名古屋大）
Eiichi Egami, Tohru Nagao, Yusei Koyama, Toru Yamada, Tadayasu Kodama, Mitsuhiko Honda,
Yoshiko Okamoto, Takafumi Ootsubo, Sunao Hasegawa, Hiroshi Shibai, Yoichi Ohyama,
Tomotsugu Goto, Akihito Suzuki, Misato Fukagawa, Daisuke Ishihara

SPICA プリプロジェクト
SPICA pre-project
松原英雄(ISAS, JAXA)、中川貴雄(ISAS, JAXA)、高橋伸宏(MDSG, JAXA)、片坐宏一(ISAS, JAXA)、
和田武彦(ISAS, JAXA)、塩谷圭吾(ISAS, JAXA)、松本敏雄(Seoul Natl. Univ.)、松浦周二(ISAS,
JAXA)、白旗麻衣、小谷隆行、大薮進喜、高木俊暢、尾中敬（東京大）、左近樹（東京大）、小林尚人（東京大）、金田英宏（名古屋大）、川田光伸（名古屋大）、
Hideo Matsuhara, Takao Nakagawa, Nobuhiro Takahashi, Hirokazu Kataza, Takehiko Wada,
Keigo Enya, Toshio Matsumoto, Shuji Matsuura, Mai Shirahata, Takayuki Kotani, Shinki Oyabu,
Toshinobu Takagi, Takashi Onaka, Itsuki Sakon, Naoto Kobayashi, Hidehiro Kaneda,
Mitsunobu Kawada
欧州・米国・韓国 Europe / US / Korea
Kate Isaak, Javier Goicoechea, Bruce Swinyard, Matt Bradford, Woong-Seob Jeong,
Myungshin Im, Hyung Mok Lee【第 2 章執筆者】[ Writers of section 2. ]86

2.2 Birth and Evolution of Galaxies:#1: Egami, Eiichi#2: Shirahata, Mai#4: Imanishi, Masatoshi#3: Nagao, Tohru#5: Koyama, Yusei

2.3 Life Cycle of Interstellar Dust
#1, #2, #3: Sakon, Itsuki#5: Kaneda, Hidehiro#4: Onaka, Takashi#6: Izumiura, Hideyuki

2.4 Studies of Exoplanets and Solar Systems#1: Enya, Keigo#2: Takami, Michihiro#4: Honda, Mitsuhiko#3: Yamashita, Takuya#5: Ootsubo, Takafumi87表 2. 天文科学コミュニティが掲げる SPICA の科学目標・成功基準（1/3）

88表 2 天文科学コミュニティが掲げる SPICA の科学目標・成功基準（2/3）

89表 2 天文科学コミュニティが掲げる SPICA の科学目標・成功基準（3/3）

90表 3. 天文科学コミュニティが掲げる SPICA のミッション要求（1/3）

91表 3. 天文科学コミュニティが掲げる SPICA のミッション要求（2/3）

92表 3. 天文科学コミュニティが掲げる SPICA のミッション要求（3/3）

93Table 2

Scientific Objectives, Targets, & Success Criteria (1/3)

94Table 2(cont.) Scientific Objectives, Targets, & Success Criteria (2/3)

95

Table 2(cont.) Scientific Objectives, Targets, & Success Criteria (3/3)

96Table 3 Mission Requirements( in terms of specification requirements) (1/3)

97Table 3(cont.) Mission Requirements( in terms of specification requirements) (2/3)

98Table 3(cont.) Mission Requirements ( in terms of specification requirements) (3/3)

99