Download - 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
GOODS: Great Observatories Origins Deep Survey
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?)
GOODS: Great Observatories Origins Deep Survey
Color selection at z>3B-band dropouts: 3.5<z<4.5
Vanzella et al. 2006
GOODS: Great Observatories Origins Deep Survey
Color selection at z>3 V-band dropouts: 4.5<z<5.5
GOODS: Great Observatories Origins Deep Survey
Color selection at z>3i-band dropouts: 5.5<z<6.5
GOODS: Great Observatories Origins Deep Survey
Color selection at z>3z-band dropouts: 6.5<z<7.5
GOODS: Great Observatories Origins Deep Survey
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.
GOODS: Great Observatories Origins Deep Survey
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.
GOODS: Great Observatories Origins Deep Survey
z~3 spectroscopy
Popesso et al., Vanzella et al. in prep.
GOODS: Great Observatories Origins Deep Survey
z~4 spectroscopy
Popesso et al, in prep.
GOODS: Great Observatories Origins Deep Survey
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?
GOODS: Great Observatories Origins Deep Survey
z~5 spectroscopy
At z~5 and 6 selection effects make “emission” galaxies easier to confirmspectroscopically
Vanzella et al. in prep.
GOODS: Great Observatories Origins Deep Survey
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.
GOODS: Great Observatories Origins Deep Survey
LBG luminosity function
Relatively mild evolution of the UV luminosity function at 2.5<z<5.5
Giavalisco et al. 2006 in prep.
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
B-dropout with n > 3.0 (spheroid-like)
GOODS: Great Observatories Origins Deep Survey
B-dropout with n~ 0.8 (disk-like)
GOODS: Great Observatories Origins Deep Survey
B-dropout with n ≥ 5 (centrally concentrated)
3" 100 x 100 pixels
3"
GOODS: Great Observatories Origins Deep Survey
B-dropout with n<0.5 (mergers, multiple cores)
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
Ellipticity distribution for different LBG profile types…….
GOODS: Great Observatories Origins Deep Survey
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?
GOODS: Great Observatories Origins Deep Survey
Star-formation in filaments of cold gas in DM halos? Ravindranath et al. 2006
35 kpc (180 comoving)
GOODS: Great Observatories Origins Deep Survey
z=4M=3x1011
Tvir=1.2x106
Rvir=34 kpc
Hydro Simulation: ~Massive M=3x1011
Kravtsov et al.
virial shock
virial shock
Dekel & Birnboim 06
GOODS: Great Observatories Origins Deep Survey
Cold, dense filaments and clumps (50%)riding on dark-matter filaments and sub-halos
Birnboim, Zinger, Dekel, Kravtsov
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
More bar signatures among LBGs at z > 2.5
Spiral arms from bar ends?
GOODS: Great Observatories Origins Deep Survey
More possible bars among LBGs at z > 2.5
Star formation at bar ends?
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
Strong clustering, massive halos
Porciani & Giavalisco 2002 Adelberger et al. 2004
=1.55r0 =3.6 Mpc h-1
GOODS: Great Observatories Origins Deep Survey
Clustering strength depends on UV luminosity:
mass drives LUV (SFR)
Adelberger et al. (2004)
GOODS Ground
Lee et al. 2006
Giavalisco & Dickinson (2001)
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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.
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
HOD at z~5
Lee et al. 2006
GOODS: Great Observatories Origins Deep Survey
The Halo Occupation Distribution at z~4
<Ng>=(M/M1)
M>Mmin
Major improvementfrom COSMOS
(Lee et al. PhD Thesis)
Lee et al. 2006
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
Inside the halo at z~4: are we seeing dwarf galaxies?
GOODS: Great Observatories Origins Deep Survey
Inside the halo at z~4: are we seeing dwarf galaxies?
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
Stellar population modeling
GOODS: Great Observatories Origins Deep Survey
Stellar population modeling
GOODS: Great Observatories Origins Deep Survey
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)
GOODS: Great Observatories Origins Deep Survey
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.
GOODS: Great Observatories Origins Deep Survey
“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)
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
GOODS: Great Observatories Origins Deep Survey
BzK samples in GOODS-N&S
GOODS: Great Observatories Origins Deep Survey
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
GOODS: Great Observatories Origins Deep Survey
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.
GOODS: Great Observatories Origins Deep Survey
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.
GOODS: Great Observatories Origins Deep Survey
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.
GOODS: Great Observatories Origins Deep Survey
VIMOS LBGs
• U
• B
• V 25 MR (Rwfi<24.5) -
• i