2018年7月23日 天文・天体物理若手夏の学校

ハッブル系列の起源
但木謙一 (国立天文台)

1. 銀河の研究について
2. 海外での研究生活について

銀河の形態と星形成活動

エドウィン・ハッブル

NASA, ESA, M. Kornmesser

銀河形態の定量化
L120

Kormendy & Bender
1996による銀河の形態分類
KORMENDY& BENDER

Vol. 464

FIG. 1.—Proposed morphological classification scheme for elliptical galaxies. Ellipticals are illustrated edge-on and at ellipticity e 3 0.4. The connection between
boxy and disky ellipticals may not be continuous (see § 4). This figure is based on the tuning-fork diagram of Hubble (1936). We make three additional modifications:
The AstrophysicalJournalSupplement
Series,(40pp),January
Kormendy& Benderwe illustrate
the two-component
natureof S0 galaxies
and198:2
label themas 2012
barredor unbarred, we call unbarred spirals “ordinary” rather than “normal”(de Vaucouleurs
1959), and we add Magellanic irregulars.

Kormendy & Bender 2012による銀河の形態分類

2. CLASSIFICATION SCHEME FOR ELLIPTICAL GALAXIES

3. EVIDENCE THAT ISOPHOTE SHAPES MEASURE ANISOTROPY

Figure 1 illustrates the proposed classification. Smoothly
connecting onto S0’s are “disky” ellipticals, i.e., those withisophotes that are more elongated along the major axis thanbest-fitting ellipses. Next come “boxy” ellipticals, i.e., thosewith isophotes that are more rectangular than ellipses. We
illustrate the classification with Hubble’s (1936) tuning-fork
diagram; clearly, it can be incorporated into de Vaucouleurs’(1959) more detailed classification.
Ellipticals with exactly elliptical isophotes are omitted; weconsider them to be intermediate between disky and boxy
ellipticals in the same way that Sab galaxies are intermediate
between the primary types Sa and Sb. However, we also showin § 4 that they are mainly face-on versions of the above twotypes. Unfavorable inclination inevitably makes classificationdifficult. For spirals, edge-on inclination is unfavorable; forOur discussion of isophote shapes follows Bender et al.
(1989, hereafter B189) and Kormendy & Djorgovski (1989).
Evidence that a4 /a measures anisotropy is summarized inFigure 2. The upper panel plots (V/ s )*, the ratio of therotation parameter V/ s to the value for an isotropic oblate
spheroid flattened by rotation (Davies et al. 1983; V is themaximum rotation velocity, and s is the mean velocity dispersion inside one-half of the effective radius). The correlation of(V/ s )* with a4 /a shows that rotation is dynamically lessimportant in boxy than in disky ellipticals (Bender 1987, 1988;
Nieto, Capaccioli, & Held 1988; Wagner, Bender, & Möllenhoff 1988; B189; Nieto & Bender 1989; Busarello, Longo, &Feoli 1992; Bender, Saglia, & Gerhard 1994). All disky
ellipticals show significant rotation, and many are consistentwith isotropic models. Boxy ellipticals have a variety of (V/ s )*銀河形態の定量化
PENG ET AL.

functional forms, which are some of the most frequently
DETAILED DECOMPOSITION
the literature. OF GALAXY IMAGES. II.

No. 6, 2010

100

V

150

200

The Sérsic profile. The Sérsic power law is one of th
frequently used functions to study galaxy morphology, a
表面輝度プロファイル
the following
form:!
"# $%&r 1/n
Σ(r) = Σe exp −κ−1 ,repixel surface brightness at the effective
where Σe isn:theセルシック指数
re . The parameter n is often referred to as the concen
n=0.5 n->isGaussian
parameter. Whenlarge, it has a steep inner profile
highly extended
wing. Inversely, when n is small,n=1 outer-> exponential
shallow innerprofile
anda steep truncation
at large radin=4-> deVaucouleurs(1/4乗則)parameter re is known as the effective radius such that hal
total flux is within re . To make this definition true, the dep
o more exotic grids than the standard
variable κ Re:
is coupled
to n; thus, it is not a free par
有効半径（50%の光が入る半径）a is in fact implicit in all 2D imageThe classic de Vaucouleurs profile that describes a num
e Figure
the axis
ratioparameter,, turns agalaxy bulges is Figure
a specialcase Ferrerof theSérsic
profilewh4. Modified
profile.
The blackreference
3. Sérsic
profilewhere re and Σqe are held fixed. Note that the larger therout= 0.5,βAs= 2,= 1000.
The redSérsic index
value n, the steeperthe
the central
core, and more extended
the outer
llipseby compressing
coordinate
4 (corresponding
to= κ100,= α7.67).
explained
below,bPeng
etandal.Σ02010
reference only in the α parameter, as indicated by the rwing. A low n has a flatter core and a more sharply truncated wing. Large Sérsic
eventhoughthefunctionalformof
theexponential
andGaussianfunctions are also special casethe green curves differ from the reference only in the βindex components are very sensitive to uncertainties in the sky background leveln every direction. In the same manner,Sérsic function when n = 1 and n = 0.5, respectively. A

parameters in the Galfit input file of Figure 1.
ified by a single Fourier mode m = 5, creating
the inner region by a truncation function, whichm = 2, with a lopsided Fourier mode of m = 1.
Fourier modes m = 1 and m = 5 is modified bycreate a lopsided, multi-armed, spiral structure.

銀河形態の定量化

円盤形 (n<2)
円盤が目立つNASA, ESA, M. Kornmesser

楕円形 (n>2)

中心部の膨らみが目立つ

銀河の形態と星形成活動
al Journal, 742:96 (20pp), 2011 December 1
Wuyts et al. 2010

‣ 星形成銀河は円盤形（n~1）‣ 星形成を止めた銀河は楕円形（n~4）‣ 120億年前（z=2.5）にすでにこの関係が成立
Table 1brightness profile shape in the SFR–mass diagram. A “structural main sequence” is clearly present at all observed epochs, and w
e of 1 and a zero point that increases with lookback time (white line). While SFGs on the MS are well characterized by exponenti
chs are better described by de Vaucouleurs profiles. Those galaxies that occupy the tip and upper envelope of the MS also have cus
een MS galaxies and red and dead systems.
f this figure is available in the online journal.)
Overview Deep Lookback Surveys

質量-光度比の影響
Wuyts et al. 2010

rophysical Journal, 753:114 (25pp), 2012 July 10

静止系紫外光静止系可視光星質量観測された画像がクランピーな構造でも、星質量の空間分布はスムーズな円盤である

Wuy

銀河の形態と星形成活動

0.5 < z < 1.5

Lang et al.

バルジ質量と星形成活動に強い相関がある
1.5 < z < 2.5

Fraction of Quenched Galaxies

The Astrophysical Journal, 788:11 (15pp), 2014 June 10

Lang et al. 2014
Figure 3. Fraction of massive galaxies (M > 1010 M⊙ ) that are quiescent (fquench ), as a function of total stellar mass (left columns), bulge mass (middle columns),
and disk mass (right columns) for z ∼ 1 and z ∼ 2. Galaxies with sSFR < 1/3 ∗ tHubble are assigned as quiescent, the others are assigned as star-forming. In the middle
and bottom rows, we split the galaxy sample in bins of B/T for the two redshift bins. Uncertainties are derived from bootstrapping and include sample variance as昔の円盤形銀河

現在の楕円形銀河（イメージ図）

進化

円盤形
活発

形態
星作り

楕円形終えたNASA, ESA, M. Kornmesser昔の円盤形銀河

現在の楕円形銀河（イメージ図）進化
形態の変化、星形成活動の停止はほぼ同時期に起きたと考えられる
一方で相関関係＝因果関係とは限らない
NASA, ESA, M. Kornmesserいつ銀河の形態が形作られたのか？

10倍銀河の中で作られる星の量銀河の屋台骨が作られた、

銀河進化史上最も重要な時代

138億年前 90-110億年前（z=1-3）（宇宙誕生）

人間でいう成長期に相当現在Madau+14

いつ銀河の形態が形作られたのか？

hysical Journal, 808:161 (12pp), 2015 August 1

Onodera et al.

星形成を止めた銀河の観測（Onodera+14）‣ 星形成を止めたのはz=22.5頃‣ 星形成のタイムスケール
は<1Gyr‣ あくまで巨大銀河の場合
夏の学校2016 招待講演
(http://astro-wakate.sakura.ne.jp/ss2015/
web/file/torape/shohtai/onodera.pdf)

lar population parameters as a function of stellar velocity dispersion (A), (C), (E), and redshift (B), (D), (F). Shown are the luminosity-weighted age
H] (C), (D), and the [α/Fe] ratio (E), (F) of stellar populations in quenched galaxies at various redshifts. In each panel, the red symbol represents ourat z§  1.6 . In the right panels, the thick and thin error bars correspond to the standard deviation and range of redshift of the sample, respectively. Blue

昔の円盤形銀河

現在の楕円形銀河（イメージ図）進化

形態の変化、星形成活動の停止はz~2の時代にほぼ同時に起きたと考えられる
NASA, ESA, M. Kornmesserいつ銀河の星形成が止まったのか？
The Astrophysical Journal, 777:18 (30pp), 2013 November 1銀河の星質量関数の赤方偏移進化（Muzzin+13）

Astrophysical Journal, 777:18 (30pp), 2013 November 1

Mstar*Bell enow cwe, w
definitbeΦ∗ inchaselecti
sinceevolve
uncertlog(Ma stea
Ithamassiv
tionof(Figurinet al.hig2TheP
growthintotwAting”;
tMstar s
thelatgalaxi
selvesupturndetermBell epopulanow ce 5. Stellar mass functions of all galaxies, quiescent galaxies, and star-forming galaxies in different redshift intervals. The shaded
σ uncertainties of the maximum-likelihood analysis, including cosmic variance and the errors from photometric uncertainties deri
ormalization of the SMF of quiescent galaxies evolves rapidly with redshift, whereas the normalization for star-forming galaxie
ular, there is almost no change at the high-mass end of the star-forming SMF, whereas there is clear growth at the high-mass en
is also evidence for evolution of the low-mass-end slope for quiescent galaxies. At low redshift, a double Schechter function fiMF.
or version of this figure is available in the online journal.)‣ 銀河は無限大に成長していない
Figure 9. Best-fit Schechter parameters as a function of redshift for combined
SMFs determined using the UltraVISTA data (red circles). The squares and‣ Mstar~1011Msolarになると、成長が止まる
is a significant improvement in the un
5. DISCUSSION
circlesarethez=0
measurements
fromColeetal.
(2001)
andBelletal.
derivedfrom
theUltraVISTA
catalog,
5.1.‣
TheCombined Population
単純にΛCDMモデルでは説明できない
area that is a factor of 8.8(2003). Also shown arecovers
parameters anfrom previous
rest-frame-optical-selected

Figure 9, we plot the evolution of the Schechter parameters, Φ∗ , and α as a function of redshift for the combined

areas used in the Pérez-González et alet al. (2009) studies, respectively. Figu

昔の円盤形銀河

現在の楕円形銀河（イメージ図）進化z~2でMstar>1011Msolarの円盤形銀河はまもなくその形態を変え、星形成を止めると期待される
NASA, ESA, M. Kornmesser

どの波長帯で形態を特徴付けるか？
z=4.3にある星形成銀河のSED

Flux density [mJy]10102101100

ダスト（赤外光度、星形成率）

ダストダスト（ダスト質量）（星形成率）

10-110-210-310-410

電離ガス（星形成率）

星（星質量）星（星形成率）-1

10010

1102103104105

Wavelength [µm]多くの場合は静止系可視（λrest~6000Å）での形態
z=1だと1.2 μm、z=2だと1.8 μm

銀河の形態と星形成活動

trophysical Journal, 742:96 (20pp), 2011 December 1WuytsWuyts et al. 2010

1. Surface brightness profile shape in the SFR–mass diagram. A “structural main sequence” is clearly present at all observed epochs, and well approx
nstant slope of 1 and a zero point that increases with lookback time (white line). While SFGs on the MS are well characterized by exponential disks, quat all epochs are better described by de Vaucouleurs profiles. Those galaxies that occupy the tip and upper envelope of the MS also have cuspier light p
diate between MS galaxies and red and dead systems.
r version of this figure is available in the online journal.)‣ HSTに観測によって、『銀河のどこに星があるか』はかなりよくわかってきた
Table 1
Overview Deep Lookback Surveys‣ 『銀河のどこで星が作られているか？』がわかFieldArea
FilterImage Depth
Sample Depth
NN(deg )(AB mag, 5σ )(AB mag)
れば、銀河の形態進化が予測できる
2

COSMOS
UDS

1.480
0.056

amorph

I814
H

27.2
26.7

b25.0
26.7

0.5<z<1.5

10608010443

c

1.5<z<2.5

21430
6796c

銀河のどこで星が作られているか？
HST観測によるHα輝線放射の分布（Wuyts+13）

hysical Journal, 779:135 (16pp), 2013 December 20

sively switched off inside these high-z galaxies,
which, given their high masses, will have toevolve into “red and dead” systems by z = 0.
We measured such quantities for a sample of
22 star-forming galaxies at a median z of 2.2 [(17)and section S1]. The sample spans a wide range
in stellar mass M ~ 4 × 109 to 5 × 1011 M⊙ andSFR ~20 to 300 M⊙ year−1 and broadly traces theages provide maps of the stellar mass densitythat is stored in such older underlying populations. Visual inspection of the two-dimensional
SFR distributions immediately reveals their notoriously irregular appearance, with bright clumps
at large radii, in contrast with their centrally
peaked and smooth stellar mass distributions(figs. S4 to S6).

early-type galaxies out to galactocentric distancesof a few kiloparsecs, corresponding to typically~2 effective radii. At these high stellar masses(~1011 M⊙), our sample of galaxies on the z ~ 2.2
have therefore already saturated their central stellar mass densities to those of galaxies of similar mass at z = 0, which are quenched systems
with a bulge-dominated morphology. Thus the

銀河のどこで星が作られているか？

VLT観測によるHα輝線放射の分布（Tacchella+15a,b）l Journal, 802:101 (32pp), 2015 April 1

Tacchella et al.

Fig. 1. Stellar mass
Mass Mand star-formation
rate surface density
distributions. The
three panels of (a) to(c) show results forthe three bins of stellar
mass indicated at the
top of each column,
z=2.38containing 9, 8, and 5
galaxies, respectively.
(A) (upper row) The
stellar surface mass
A(a)
A(b)
A(c)
density profiles (red,B(a)
B(b)
B(c)
scale on the left vertical axis) and SFR surface density profiles(blue, scale on thez=2.39right vertical axis) for
our z ~ 2.2 sample.
Thin lines represent
individual galaxies; themean values are givenby the solid circles(with error bars indicating the 1s scatter).
C(a)
C(b)
C(c)
The derivations of
z=2.45these profiles aredescribed in detail inthe supplementarymaterials (17). (B) (middle row) The mean sSFR as a function of radius r (sSFRr; black line). In gray we show the 1s scatter. (C) (bottom row) The averagesurface stellar mass density profiles of the star-forming z ~ 2.2 galaxies (red points with dashed line; error bars indicate the 1s scatter) overplotted on theaverage profiles for the mass-matched samples of z = 0 galaxies (colors indicate morphological types: orange for early types, blue for late types).

‣ 星形成領域（Hα輝線）は星の分布より広がっている‣ 中心部に比べて、外側で星形成（SFR/Mstar）が活発‣ inside-out quenching
SCIENCE sciencemag.org

17 APRIL 2015 • VOL 348 ISSUE 6232

315

years in the galactic peripheries.
The galaxies will be fully quenchedby z ~ 1. The solid orange line indicates the mean quenching time for all galaxies in the highest-mass bin,whereas the orange-shaded region marks the 1s scatter.

銀河のどこで星が作られているか？

銀河の形態進化とクエンチング（Tacchella+15a）

Fig. 4. Proposed sketch of the evolution of massive galaxies. Our results suggest a picture inwhich the total stellar mass and bulge mass grow synchronously in z ~ 2 main sequence galaxies,
and quenching is concurrent with their total masses and central densities approaching the highest
values observed in massive spheroids in today’s universe.

形態進化?

クエンチング‣ 星形成領域（Hα輝線）は星の分布より広がっている
sciencemag.org SCIENCE‣ 中心部に比べて、外側で星形成（SFR/Mstar）が活発‣ inside-out quenchingダスト減光問題
遠方銀河
軽い星（年老いた） 塵重い星（生まれたばかり）電離ガス

可視光線
遠赤外線サブミリ波
紫外線

Hα輝線

ダスト減光問題
ダスティー

The Astrophysical Journal, 850:208 (11pp), 2017 December 1Whitaker et al.
Whitaker et al. 2017

Figure 2. Fraction of obscured star formation relative to total derived from median stacks is a strong function of M and does not evolve strongly out to z=2.5. Left:linear y-axis version, comparing to a local SDSS sample based on GALEX/WISE photometry at 0.02<z<0.05 in grayscale (R. Cybulski et al. 2017, inpreparation). We additionally compare to 450 and 850 μm SCUBA-2 stacks of a mass-selected sample from Bourne et al. (2017), ﬁnding excellent agreement at themassive end (squares). The Herschel imaging from Casey et al. (2014b) agrees at the massive end down to the limits of the FIR-selected sample of star-forming
galaxies (triangles). The dotted–dashed line represents the implied ratio based on UV light attenuation measurements by Pannella et al. (2009). Right: logarithmic
y-axis version, including grayscale contours of the individual 3D-HST measurements in addition to the median stacks (circles) from Whitaker et al. (2014). The thinlines represent the completeness limits of the 24 μm imaging. The dashed line is the average relation when using the Murphy et al. (2011) SFR calibrations.

‣ 重い銀河ほどUV光は吸収され、IRで再放射されている‣ Mstar>1011Msolarの星形成銀河では、UVやHα輝線は星形成の指標として不定性が大きい‣ ダストの連続光を観測すれば良い
only weakly (Df˜obscured < 0.04) for a correspondingly largechange in the log(sSFR) limit.
The mode of the SDSS distribution in Figure 2 (right) tracks
the higher-redshift data well, but with a broader distribution. InFigure 2, there appears to be a dearth of highly obscured lowmass galaxies at z ~ 0 . We forgo interpretation of theindividual distributions at the lowest M due to complications
by the completeness limits of both data sets. For obscuration

ダスト減光問題
z~2にある星形成銀河 (Tadaki+2017)
MIPS/24um

PSF=6″

PACS/160um

PSF=12″?

0.2″‣ 中間赤外・遠赤外の観測はスペースからの観測になる
ため空間分解能が悪い‣ 8 kpc程度（~1 ）の遠方銀河を分解するには、これらより遥かに高い空間分解能が必要

Going to ALMA observations

ESO/NAOJ/NRAO

ダスト減光問題
z~2にある星形成銀河 (Tadaki+2017)
MIPS/24um

PSF=6″

PACS/160um

PSF=12″

ALMA/870um

PSF=0.2″‣ 圧倒的に高い空間分解能でダスト連続光を観測‣ 銀河のどこで星が作られているか直接観ることが可能

銀河のどこで星が作られているか？

ハッブル（可視光）
若い星
弱い星形成現場

ハッブル（近赤外線）

アルマ（電波）ちり星の総量星の材料となる塵

銀河の形

激しい
星形成現場

HSTで観る遠方銀河
Tadaki+2017

84

R1/2 [kpc]

21

0.5

HST/H
10.8

11.0

11.2

11.4

log M * [Msola r ]‣ 円盤形（n~1）で広がっている（Re=3-6 kpc）

HST & ALMAで観る遠方銀河
Tadaki+2017

84

R1/2 [kpc]

2
10.5

HST/H
ALMA/870um
10.8

11.0

11.2

11.4

log M * [Msola r ]‣ 円盤形（n~1）で広がっている（Re=3-6 kpc）
‣ 中心1kpcで激しい星形成ガスが銀河の中心に運ばれている

銀河の進化を予測する円盤で星が生まれている場合

円盤形の銀河

もっと円盤が目立つ銀河に中心部で星が生まれている場合

円盤形の銀河

中心の膨らみが目立つ銀河にbulge formation
inside-out
quenchinginside-out
growth phase