高分解能観測で探るマゼラン雲の星形成

Norikazu Mizuno, Toshikazu Onishi,and NANTEN team(Nagoya University, Japan)
1. NANTEN results of Magellanic Clouds
2. SEST results of Magellanic Clouds
3. CO Observations towards Magellanic Bridge
3. Future prospects (NANTEN2, ASTE, ALMA)

マゼラン雲研究の特徴• 一つの銀河全体の分子ガスの分布– 同じ空間分解能、近い、Face-on• 星団形成の仕組み– Populous Cluserの存在• 原始銀河に近い環境下での星形成– 重元素量：銀河系 > LMC > SMC > Bridge• 現状：GMCの分布が明らかに->高分解能観測Why Magellanic Clouds ?

690 kpc

Nearest bigger galaxies, relative face-on location (LMC)
We can resolve individual GMCs!
Different interstellar environment
lower metallicity, higher gas to dust ratio, strong UV field
Active star formation
populous clusters, huge HII regions (e.g., 30Dor…)

NANTEN telescope in Chile

Since 1996

•Diameter: 4m
CFRP + conductive paint•SIS receiver + AOS backend•85-115GHz, mainly CO(J=1-0)•Beam size 2.6 arcmin (@115GHz)~ 40 pc@50kpc•Velo. Res. 0.1 or 0.6 km/s
•Band Width 100 or 500 km/s
•Tsys ~ 300 K (SSB)

Las Campanas Observatory

270 CO clouds
identified(M > 104 Msun)
Total molecularmass~ 7×107 Msun

500 pc

Properties of giant molecular clouds

c.f. for Galactic clouds
dN/dMCO ~ MCO –1.5
(e.g., Solomon et al. 1987 )Distributions of clusters and CO clouds

Youngest clusters（<10 Myr ）Young clusters（10Myr < 30Myr）
Bica et al. 1996

HPBW

HII regions
Davies et al. 1976

103 CO clouds ( > 105 Msun)
Evolutional time scale~ 3 Myr~ 3 Myr~ 3 MyrM33 BIMA Observations (linear resolution 50 pc)

Engargiola et al. 2003
Rosokowsky et al. 2003

・148 GMCs detected
・More than 2/3 of the GMCs have associated HII regions
・Steep index for mass spectrum ~ -2.6

SEST observations for the LMC
Collaborators
L.E.B. Johansson, S. Nikolic, R.S. Booth, L.A. Nyman (OSO)
SEST 15 m
Beam size45" (10 pc) (115 GHz)23" (5 pc) (230 GHz)
Mapping 12CO (J=1-0/2-1)
grid 40 " （cloud）
20 " （peak）
13CO (J=1-0/2-1), C18O(2-1),

HCO+, HCN, HNC, CS

NANTEN (40 pc)

SEST (10 pc)

NANTEN results of the SMC

Mizuno et al. 2001

Search for CO in the Magellanic Bridge

SMCShapley’sWing, SMC tail

LMC

Putman et al. 1998

マゼラニック・ブリッジ ~環境~
中性水素ガス（HI）で見たマゼラン銀河 (Putman et al.1998)

ブリッジ

Galactic latitude (degree)

-45
SMC

質量は108太陽質量
Putman et al. （1998）-40

内部に星が存在している

LMC

Irwin et al. （1985）
Grondin et al. （1990）

MagellanicBridge-35

分子雲中での-30

星形成？？？
280

290

300

Galactic longitude (degree)観測諸元
名古屋大学「なんてん」電波望遠鏡

口径：4m
観測ライン：12CO(J=1-0)
周波数：115GHz
ビームサイズ：2’.6⇒50pc@60kpc
システム雑音温度：220K
速度分解能：0.1km/s
rms:0.009K@0.1km/s
積分時間：約8時間/1点
観測時間：約20時間/1点
観測期間：(@チリ・ラスカンパナス天文台)

2002/10〜2003/7

Galactic Warp
Nakagawa et al. （2004）

500z(pc)

0-500-1000-1500

Color:HIRed cross:CO

10141618R(kpc)

銀河系の中では重力場が弱く、重元素量が低い

20

考察
Putman et al.（1998）

M(HI)~7×107太陽質量

SMC

dGM total(∆V) ≈d2∆V~15km/s、d~2kpc ⇒M(total)〜108太陽質量

Sub-millimeter observations ofthe Magellanic Clouds
・Structure and evolution of GMCs in the metalpoor environment- CI observations- Comparison with the galactic GMCs
・Reveal the properties (density, temperature, size) ofdense clumps in the GMCs
- CO (J=7-6, 4-3, 3-2)

NANTEN2ASTE

これからのマゼラン雲観測• 高分解能観測– 0.1 arcsec = 0.024pc– 銀河系内のGMCとの比較が可能– 0.01arcsecの分解能ならProto-cluster形成の現場が見える。

• YSOsの探査– 現状は極めて貧弱– IRSF/SIRIUS, ASTRO-F, Spitzer

NANTEN→NANTEN2z Large scale survey of interstellar gas
in the Galaxy and Magellanic Cloudsin CI (3P1- 3P0), CI (3P2- 3P1)
and CO (J= 2-1, 3-2, 4-3, 7-6)
• Move NANTEN telescope to Atacama, ChileAlt. 4,800m starting from November 2003
• Replace the main-ref for higher-freq. operation• Enclosed in a DomeSummary
1. Giant molecular clouds in the Magellanic Clouds are similar toour own in mass etc., except for the apparent CO depletion.
2. The mass spectrum of GMCs in the LMC is steeper than that of
the galactic disk.
3. Very young clusters have been identified by comparing with CO.
The SFE is likely around several to a few %.
4. Starless GMCs have been identified.
5. Formation of stellar clusters is very rapid, and they are efficientin dissipating the parent molecular clouds.
6. CO was detected in the Magellanic Bridge.
7. CI observation has been started with ASTE.