Star Formation in High Redshift Galaxies

Star Formation in High Redshift Galaxies

Mauro GiavaliscoSpace Telescope Science Institute

and the GOODS Team

GOODS: Great Observatories Origins Deep Survey



Finding high-redshift galaxies:color selection

B435 V606 z850

Unattenuated Spectrum Spectrum

Attenuated by IGM

B435 V606 i775 z850

z~4

1. Color selection is very efficient in finding galaxies with specific spectral types in a pre-assigned redshift range

2. Wide variety of methods available, targeting a range of redshifts, galaxies’ SEDs:• Lyman and Balmer break

(Steidel, Adelberger, MG)• DRG (Franx, Labbe et al.)• BzK (Daddi et al.)• Photo-z (Mobasher et al)

Here, the case of “Lyman-break galaxies” GOODS yielded the deepest and

largest quality samples of LBGs at z~4 to ~6 (7?)


Color selection at z>3B-band dropouts: 3.5<z<4.5

Vanzella et al. 2006


Color selection at z>3 V-band dropouts: 4.5<z<5.5


Color selection at z>3i-band dropouts: 5.5<z<6.5


Color selection at z>3z-band dropouts: 6.5<z<7.5


The Redshift Distribution

#183

#27

LBGs at z>3 are targets of the ongoing GOODS spectroscopic time with the ESO VLT and Keck

Vanzella et al. 2006, 2005, 2006 in prep.Stern et al. 2006 in prep.


z~4 spectroscopy

Variety of spectral “types”

Very similar to the z~3 galaxies

Emission of Lya observed together with weak interstellar absorption lines

Stronger absorption lines are present when Lya is obsered in absorption

Effect of geometry of ISM?

Vanzella et al., in prep.


z~3 spectroscopy

Popesso et al., Vanzella et al. in prep.


z~4 spectroscopy

Popesso et al, in prep.


Exploring the geometry of the ISM

Abs.Em.No obvious correlation of spectral

“types” with UV color or ellipticity of the galaxies

Whatever causes the absorption does not know about the geometry of the UV-luminous galaxy

Outer ISM phase surrounding the UV-emitting regions whose spatial geometry DOES NOT correlate?


z~5 spectroscopy

At z~5 and 6 selection effects make “emission” galaxies easier to confirmspectroscopically

Vanzella et al. in prep.


Composite spectrum ofi-band dropouts

The spectral properties of “observed” LBGs at z~6 are very similar to some LBGs observedat z~3.

At z~6 it is very hard to obtain spectra of those LBGs with no Lya. Selection effect!

Vanzella et al., Giavalisco et al 2006, in prep.


LBG luminosity function

Relatively mild evolution of the UV luminosity function at 2.5<z<5.5

Giavalisco et al. 2006 in prep.


The history of the cosmic star formation activity:

This plot spans 94% of the cosmic time!

We find that at z~6 the cosmic star formation activity was nearly as vigorous as it was at its peak, between z~2 and z~3.

Giavalisco et al. 2004Giavalisco et al. 2006, in prep.

=-1.6 assumed


Star formation rates

Derive from far-UV continuum luminosity

Dust obscuration correction:

Calzetti starburst obscuration law

Some rates are low, like z~0 spirals;other are prodigiously high

But, does “corrected UV” trace SF well?

Quite likely in these systems (Kennicutt et al., Calzetti et al 2006; also Dickinson’s talk)

z~4 B-band dropouts


The morphology of the LBGs

Giavalisco et al. 1994, 1996, 1998Steidel, Giavalisco, Dickinson & Adelberger 1996;Lowenthal et al. 1997; Dickinson 1998; Giavalisco 1998;Papovich, Giavalisco, Dickinson, Conselice & Ferguson 2003Papovich, Dickinson, Giavalisco, Conselice & Ferguson 2004

•Smaller•Regulars,•Irregulars,•Merging,•Spheroids?•Disks?•No Hubble Seq.•No -dependence

Rest-UV light Rest-optical lightMorphology does not depend much on wavelength: young systems


Galaxies get smaller at high redshift…

Standard ruler

R~H(z)-2/3

R~H(z)-1

First measures at these redshiftsTesting key tenets of the theory

Galaxies appear to grow hierarchically

Ferguson et al. 2004


Surface Brightness Profile Analysis:

• allows convolution by the point spread function

• better handle on flux in the galaxy wings where S/N drops at low surface brightness levels

• Measurement biases minimized

- 2-D modelling using a single Sérsic function:

Exponential disks: n = 1

R1/4 spheroids : n = 4

Quality control: low chi2, small errors on parameters, mfit = mauto±0.5

[Ravindranath et al. 2006]

GALFIT


B-dropout with n > 3.0 (spheroid-like)


B-dropout with n~ 0.8 (disk-like)


B-dropout with n ≥ 5 (centrally concentrated)

3" 100 x 100 pixels

3"


B-dropout with n<0.5 (mergers, multiple cores)


Profile Distribution of LBGs and z=1.2 starbursts (all M<0.5MUV*)

LBGs at z > 2.5:

~ 40% exponential disks

~ 30% spheroid-like

~ 30% mergers, multiple cores

Star - forming galaxies at z = 1.2:

~ 26% exponential disks

~16% spheroid-like

~ 58% mergers, irregulars?

Similar conclusions from non-parametric study based on GINI, M20 and CAS coefficientsLotz, Madau, Giavalisco, Primack & Ferguson 2005


Probing the Intrinsic Shapes Through Ellipticity Distribution

Observed peak in the = (1- b/a) , and skewed distribution

Not only spheroids and circular disks seen at random orientations

Intrinsically elongated galaxies

Peak is lower at lower z


Ellipticity distribution for different LBG profile types…….


Possible explanations for the excess of “Elongated” morphologies among LBGs !

Rotation-dominated disks? Edge-on projections and selection effects

Star forming clumps along gas-rich filaments of cold gas infall in DM halos

High-z bars at early epochs of galaxy formation?


Star-formation in filaments of cold gas in DM halos? Ravindranath et al. 2006

35 kpc (180 comoving)


z=4M=3x1011

Tvir=1.2x106

Rvir=34 kpc

Hydro Simulation: ~Massive M=3x1011

Kravtsov et al.

virial shock

virial shock

Dekel & Birnboim 06


Cold, dense filaments and clumps (50%)riding on dark-matter filaments and sub-halos

Birnboim, Zinger, Dekel, Kravtsov


Observing the first gas-rich bars among LBGs at z > 2.5?

Classic bar morphology in the first few billion years!

Bar in DGs encompasses the whole galaxy; ~2-3 kpc scalelength

Ravindranath et al. 2006


More bar signatures among LBGs at z > 2.5

Spiral arms from bar ends?


More possible bars among LBGs at z > 2.5

Star formation at bar ends?


The mass of LBGs: spatial clustering

• Galaxies at high redshifts have “strong” spatial clustering, i.e. they are more clustered than the z~0 halos “de-evolved back” at their redshift.– High-redshift galaxies are biased, I.e. they occupy only the most

massive portion of the mass spectrum.– Today, the bias of the mix is b~1.

• Idea is to test key tenets of the gravitational instability paradigm– evolution of galaxy clustering contains information on how the

mass spectrum gets populated with galaxies as the cosmic time goes on.

– Clustering of star-forming galaxies at a given redshift contains information on relationship between mass and star formation activity


The mass of LBGs: spatial clustering

Giavalisco et al. 1998Steidel et al. 2003Adelberger et al. 1998

r0=3.3+/- 0.3 Mpc h-1

= -1.8 +/- 0.15


Strong clustering, massive halos

Porciani & Giavalisco 2002 Adelberger et al. 2004

=1.55r0 =3.6 Mpc h-1


Clustering strength depends on UV luminosity:

mass drives LUV (SFR)

Adelberger et al. (2004)

GOODS Ground

Lee et al. 2006

Giavalisco & Dickinson (2001)


Clustering segregation at z~4 and 5

Lee et al. 2006See also Ouchi et al.2004, 2006

Clustering segregation is detected in the GOODS ACS sample at z~4


Halos and Galaxies at z~3-5:Evidence of Evolution?

Clustering scaling in good agreement with hierarchical theory

Implied halo mass: >5x1010 MO(faint samples) >1012 MO (bright samples)

1-σ scatter between mass and SFR ~smaller that 100%

LBG halos at z ~ 5 are less Massive.

Specific star formation higher at higher redshift. Up-sizing! Giavalisco & Dickinson 2001

Porciani & Giavalisco 2002Adelberger et al. 2004; Lee et al. 2006


Implications

• Halo mass, I.e. local gravity, is a key parameter to control star fomation

• Relationship between mass and star formation is tight

• Possible to reconstruct the LUV(MH) distribution function (e.g. CLF)

Giavalisco & Dickinson 2002;Lee et al. 2006 in prep.


Halo sub-structure at z~4

ACS depth made possible to observe structure within the halo.

Break observed at ~10 arcsec

Note: 10 arcsec at z~4 is about ~350 kpc, about the size of the virial radius for M~1012 Mo .

Lee et al. 2006; see also Ouchi et al. 2006


HOD at z~5

Lee et al. 2006


The Halo Occupation Distribution at z~4

<Ng>=(M/M1)

M>Mmin

Major improvementfrom COSMOS

(Lee et al. PhD Thesis)

Lee et al. 2006


Halos and Galaxies at z~4

Lee et al. 2006

Halo substructure:we observe an excess of faintgalaxies around bright ones.massive halos contain morethan one LBG

“Bright Centers”: z_850<24.0“Faint centers”: 24.0< z_850 <24.7“Satellites”: z_850 >25.0

Substructure is observedwith good S/N at faint luminosity L<L*/2


Inside the halo at z~4: are we seeing dwarf galaxies?


Inside the halo at z~4: are we seeing dwarf galaxies?


Conclusions

• With large samples of high-z galaxies it is possible to test key ideas on star formation and galaxy evolution

• LBGs at z>4 have mix of spectroscopic properties– Tracing geometry of ISM

• Relatively high SFR; mild evolution of the UV lum. density at high z• Mix of UV morphology

– Spheroid and disk-like systems observed – Higher fraction of irregular systems at z~1.5 than at z>3– Intrinsic excess of elongated systems that disappear at lower redshifts

• Evidence of cold accretion in filaments?• Large-scale bars?

• Size evolution consistent with hierarchical growth• Detected halo sub-structure at z~4 (thanks to ACS sensitivity)

– Proving key prediction of theory


Color selection at z~2Distant Red Galaxies (DRGs):

J-K>2.3

F(24m) & z -> LIR using Chary & Elbaz 2001 templates

X-raydetected

GTO 24m50% completeness

• UV-IR SEDs span range of Hubble sequence or dusty galaxies, (Forster-Schreiber et al.)• 50% detected with F(24m)>60 Jy. SEDs consistent with either AGN or starbursts.• 24m-detected DRGs are typically ULIRGs (LIR >1012 Lo)

Papovich et al. 2005


DRGs at z~2

Galaxies selected from near-IR photometry [(J-K)>2.3]

Most would NOT be selected by LBG criteria (UV selection)

However, overlap with LBG not quantifiedAnd certainly significant (see Adelberger Et al. 2004).

They appear in general more evolved, I.e.more massive (larger clustering), with larger stellar mass, more metal rich, and more dust obscured) than LBGs. Occurrence of AGN also seems higher.

At z~3 these galaxies have about50% of the volume density of LBGs (highly uncertaint). However; they possibly contribute about up to 100% of the LBG stellar mass density, becausethey have higher M/L ratios Van Dokkum et al. 2004


IRX- for Distant Red Galaxies

UV spectral slope measured from ACS colors.

DRGs typically have redder than LBGs: <A1600> = 3.1 mag

LIR for DRGs typically exceeds expectation from LUV and by factors of 10-100x

DRG IR excess larger than that for less luminous (typically more UV-bright) HDFN 24m sources.

SFR~10 to 1000 Mo/yr


Stellar population modeling


Stellar population modeling


Stellar masses & properties of GOODS-S DRGs

Typical DRG stellar masses ~few x 1011 Mo,

(cf. FIRES work).

GOODS-S sample is roughly complete at >1011 Mo for 2 < z < 3

2-component models frequently (but not always) give better fits to the photometry. Masses increase, but not as much as for blue, lower-mass HDFN LBGs.

Loosely dividing by reddening: Heavily obscured: EB-V > 0.35: • < z > = 1.7• LIR ~ expected from LUV, Lightly obscured: EB-V < 0.35:• < z > = 2.5• LIR >> expected from LUV, (for 24m-detected objects)


Specific star formation rates (SSFRs)

Low-z comparison samples from COMBO-17: z ~ 0.4 and z ~ 0.7

• Stellar masses estimated from COMBO-17 photometry• SFRs from GTO MIPS 24m data

z < 1: galaxies with M > 1011 Mo tend to be forming stars at low SSFRs.

z > 1: Galaxies over a broad range of masses tend to span a broad range of SSFRs, with many DRGs forming stars prodigeously.


“Downsizing” of star formation in massive galaxies

Treating COMBO-17 and GOODS DRG samples as representative for M > 1011Mo:

z~2.3 DRGs forming stars with SSFR > cosmic average

z < 1 massive galaxies forming stars more slowly than the global average

Further evidence that 1.5 < z < 3 was a key era for the rapid growth of stellar mass in the most massive galaxies.

Global average from co-moving SFR(z)


Color selection at z~2: BzK galaxies

BzK selection well suited for 24m MIPS studies:• Selected range 1.4 < z < 2.5 places strong mid-IR features in 24m band• Color selection includes objects with red UV continuum, e.g., from extinction• K-band selection suitable for relatively massive galaxies

(Daddi et al. 2005)

BzK selection: 1.4<z<2.5



BzK samples in GOODS-N&S


24m detection of BzK galaxies

245 BzKs with K < 20.6169 BzKs with K < 20

At present, spectroscopic redshifts available for only a few; Keck LRIS+DEIMOS runs ongoing.

36/169 detected in hard X-rays (mostly AGN; not considered for now)

109/133 (82%) for non-Xray BzKs detected at 24m(undetected fraction consistent with expected number of “passive” BzKs)

Median <f24> = 110 JyFainter K-band --> fainter 24m


Multi-wavelength measures of SFR

MIPS: <f(24m)>=125 Jy, <z>=1.9, and CE01 templates: <LIR> = 1.7e12 Lo, <SFR> ~ 300 Mo/yr

UV continuum + reddening: <SFR> ~ 220 Mo/yr

Radio: stacked VLA data <f(20cm)> = 17 Jy<LIR> = 2e12 Lo, <SFR> ~ 340 Mo/yr

Sub-mm: stacked <f(850m)> = 1.0 mJy (5) <LIR> = 1.0e12 Lo, <SFR> ~ 170 Mo/yr

X-ray: stacked 8.5 soft-band detection, no significant hard-band. Far below expected AGN level. <SFR> = 100 - 500 Mo/yr (Persic 2004, Ranalli 2003 conversions)

On average, multi-wavelength SFR tracers agree reasonably wellwith expectations from low-z correlations, templates & analogs.


UV vs. IR SFRs: BzK-selected galaxies at z ~ 2

B-band samples ~1500A UV continuum at z~2; B-z measures UV continuum slope.

f(24m) / f(B) correlates strongly with B-z color, as expected if UV continuum slope results from dust reddening. Log scatter is a factor of ~3 (including effects of the broad BzK z-range).

Brighter/more luminous mid-IR sources (LIR > 1012 Lo) tend to exceed expected IRX-, while less luminous sources match or fall below it (possibly including “passive” BzKs.

Measure of mass in progress.


Star formation at z~1.5 – 2.5

• Typical BzK and DRG galaxies appear to be both massive (~1011 Mo) and rapidly star forming (LIR ~1012 Lo, ~ 200 Mo/yr), with space density ~1000x larger than present-day ULIRGs

• 10-20% may be AGN; X-ray stacking favors star formation for the majority.

• ~ 80% MIPS detection rate for BzKs implies that most massive galaxies at 1.4 < z < 2.5 are forming stars prodigiously:– Implies high duty cycle for SF – Substantial mass build-up over this redshift range

• BzKs should form* >~ 5x107 Mo/Mpc3 over ~2 Gyr, comparable to local stellar

mass density in galaxies with M* > 2x1011 Mo

• Specific star formation rate (SFR/M*) for massive (>1011 Mo) galaxies at 2 < z < 3 is much higher than at z < 1 and than cosmic average -> downsizing.


VIMOS LBGs

• U

• B

• V 25 MR (Rwfi<24.5) -

• i

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Star Formation in High Redshift Galaxies

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