The cosmic evolution of star formation and metallicity over the last 13 billion years
(an observational perspective)
Andrea Cimatti (INAF - Osservatorio Astrofisico di Arcetri)
OUTLINE
SFR indicatorsHigh-z star-forming galaxies“Fossil” galaxies
Cosmic evolution of SF densityCosmic evolution of stellar mass“Downsizing”
Metallicity indicatorsMetallicity of high-z galaxiesCosmic evolution of the mass-metallicity relation
The 1996+ revolution
HST
ESO VLT JCMT
Keck
The “historical” Lilly – Madau plot
Lilly et al. 1996 Madau et al. 1996
Star formation rate (SFR) main indicators
L(recombination lines) (e.g. Hα) (primary)L(forbidden lines) (e.g. [OII]3727) (empirical, not universal) L(Lya)L(UV continuum) from OB stars (1500-2800 Å)
L(FIR) (and L(MIR) ?) (10-1000μm)L(radio) (1.4 GHz) L(X) (2-10 keV)
Caveat: AGN “contamination”, dust extinction, IMF assumption
Specific star formation rate = SSFR = SFR/(stellar mass) [yr-1]
Small SSFR most mass was already built-up in the pastLarge SSFR significant mass is still building
Star formation
The star formation that we see:
high-z galaxies which are forming stars
Optical selection based on broad-band colors
Steidel et al. 2005
Magenta (“BM” selection): 1.5 < z < 2Cyan (“BX” selection): 2 < z < 2.5Yellow+Green (LBG selection): z ~ 3
BM BX LBG
Optically-selected star-forming galaxies at 1<z<4
(Shapley et al. 2003)
< log M(stars)/Msun > = 10.3 ± 0.5
< SFR > = 30 ± 20 Msun/yr
0 < E(B-V) < 0.3
N ~ 3x10-3 Mpc-3
1/3 < Z/Zsun < 1
(Steidel et al. 2004, Reddy et al. 2005, Shapley et al. 2003, 2005, Erb et al. 2006)
Selected in the optical with the so called BM/BX/LBG color criteria (Steidel et al. 1996, Adelberger et al. 2004)
Photometric candidates at 7 < z < 10
HUDF data. Bouwens et al. 2004, 2005
No secure genuine “primordial” (Pop III)objects identified to date
…
K- to mm-selected dusty starbursts (1<z<5)
E(B-V)>>0.3< log M(stars,,gas)/(Msun) > ~ 11SFR ~ 100-(1000) Msun/yr, Z ~ ZsunN ~ 10-4 Mpc-3 (10-5 for submm galaxies)
Problem for galaxy formation models
(dEROs, SMGs, DRGs, sfBZKs, HyEROs, IEROs…;Totani et al. 2001, Cimatti et al. 2002, Daddi et al. 2004, Chapman et al. 2005; Franx et al. 2003; Chen et al. 04)
SpitzerIRAC-EROs
Submm/mm galaxiesK-selected starbursts
Dusty EROs
High-z dusty AGN
Dust thermal emission from a quasar at z=6.42 CO(3-2) emission from the same quasar(Bertoldi et al. 2003) (Walter et al. 2004)
Many high-z quasars have high FIR luminosity (up to 1e13 Lsun), dust continuum emission consistentwith mass of ~ several x 1e8 Msun and molecular gas with mass of the order of 1e10 MsunSFR > 1000 Msun/yr !?
Emission line galaxies
Line emitting galaxies are generallyfound with narrow-band imaging or “slitless” spectroscopy (1 < z < 6.6)
McCarthy et al. 1999, Hu et al. 2002, Glazebrook et al. 2004, Kurk et al. 2004,Malhotra et al., Rhoads et al. , Taniguchiet al. 2005, Bunker et al., Doherty et al. 2006
Lya at z=6.56 (Hu et al. 2002)
Kurk et al. 2004
Lya at z=6.54
OPTICAL SELECTION
NEAR-IR SELECTION
The star formation that we do not see:
“fossil” galaxies which had star formation
Old passive spheroids at z>1
E/S0 galaxiesPassively evolving1 < z < 21 – 4 Gyr oldM(stellar) > 1011 Msun
Problem for galaxy formationmodels
z(SF onset) > 2 – 3Short-lived, powerful starbursts
It is possible to derive SF history from spectra
Cimatti et al. 2002, 2004, McCarthy et al. 2004, Daddi et al. 2005, Saracco et al. 2005
A massive galaxy candidate at z~6.5
Photometric candidate (no spectroscopic redshift)Consistent with a galaxy at z=6.5 with a large stellar
Stellar mass of 6e11 Msun (!) z(form) > 9
Alternative: very dusty starburst at z=2.5
(Mobasher et al. 2005)See also Eyles et al. 2005, Yan et al. 2006
Other massive galaxy candidates at 5 < z < 8
z J H K 3.6 4.5 5.8 8.0 24 micron
HST ACS: B+V+I+zK ≥ 25 (AB)
STACKING (3”x3”)
Rodighiero et al. 2006
The cosmic evolution
The Lilly-Madau plot 10 years ago
The Lilly – Madau plot now
Hopkins et al. 2005, 2006
Hatched and green: 24μmRed star: radioBlue: optical/UV
DLAs
Cosmic evolution from “archeology” of z~0 galaxies
Heavens et al. 2004
SDSS data + MOPED
Dependence on luminosity and sample selection
K-selected samples miss a significant fraction of SF galaxies with L<L*At all z, L>L* galaxies contribute only 1/3 to the SFR densityL<L* galaxies are the dominant sites of star formationSFR density ~constant at 1<z<4, drops by 2x at z~4.5(Gabasch et al. 2005)
“Downsizing” (Cowie et al. 1996)
Thomas et al. 2004
Constraints from σ, Hβ, Mgb, <Fe>, stellar populations
More massive spheroids form earlier and fasterFormation time scales independent of environment~1-2 Gyr younger in low density environmentsMass assembly almost completed around z~1
(see also Cimatti, Daddi & Renzini 2006)
Dependence on mass and environment
Mass-dependent SFHs for z~0 galaxies(Heavens et al. 2004)
Latest results confirm that massivegalaxies which dominated cosmic SFat z~3 are in clusters today, whereasgalaxies dominating SF at z~0 inhabit low density regions (Poggianti et al. 2006,Sheth et al. 2006)
Early-type galaxies
The evolution of the stellar mass function
Stellar mass function evolution pergalaxy type (Bundy et al. 2006)Shaded areas = 1 σ confidence regions
Increase of N(red) mirrored by decrease of N(blue)
Fractional contributions of red and bluegalaxy populations to the stellar mass function
Largest sample analyzed to date:DEEP2 spectroscopy + optical-NIR SEDs>8000 galaxies over 1.5 square degrees (4 fields)
M(tr)
Specific star formation
Feulner et al. 2005
SSFR = SFR/M(stars)
Higher in lower massgalaxies at all redshifts
Oldest stars in largestmass galaxies
Massive galaxiesare in a quiescent stateat z<2 (no significantchange in stellar mass) Strong increase of<SSFR> at z>2-3 for most massive galaxies
Downsizing of SF
See also Juneau et al. 2005,Caputi et al. 2006
Metallicity
Metallicity indicators
IONIZED GAS
R23 = ([OII]3727+[OIII]4959,5007) / Hβ (Pagel et al. 1979)N2 = [NII]6584 / Hα (Denicolò et al. 2002)O3N2 = ([OIII]5007/Hβ)/([NII]6584/Hα) (Pettini & Pagel 2004)R23 + [OIII]5007/[OII]3727 (Nagao et al. 2006)[NeIII]3869/[OII]3727 (Nagao et al. 2006)
CAVEAT: shock-ionized gas, AGN photoionization
ISM and STARS
Optical absorption features in E/S0 galaxies (e.g. Lick indices, Fe4383)Iron absorption lines at 2000-3000 Å (e.g. Savaglio et al. 2004)UV absorption features (e.g. 1370 Å, 1425 Å, 1978 Å, Rix et al. 2004)Metal absorption lines in DLAs (e.g. Pettini et al. )
Nagao et al. 2006 Emission line indicators
Stellar mass – ionized gas metallicity relation
Tremonti et al. 2004 (SDSS)
Stellar vs. ionized gas metallicity
Gallazzi et al. 2005 (SDSS)
Mass – metallicity relation at 0.4 < z < 1.0A M-Z relation exists at <z>~0.7 and evolves with redshiftAt a given mass, a galaxy at z~0.7 has lower metallicity vs. z~0Evolution more rapid at lower masses. Massive galaxies have Z(solar) at z~0.7 (bulk of SF completed)A more rapidly declining SF in more massive galaxies is consistent with the results (downsizing…)
(see also Carollo & Lilly 2001, Lilly et al. 2003, Kobulnicky & Kewley 2004, Maier et al. 2004, 2006)
Savaglio et al. 2005(CFRS + GDDS samples)
Optically-selected star-forming galaxies at z~2
Shapleyet al.2004
Erb etal. 2006
Mass – metallicity relation at z~2
Erb et al. 2006Optically-selected
Metal-rich starbursts at z>2
Submm galaxies (Tecza et al. 2004, Swinbank et al. 2005) Distant Red Galaxies (J-K>2.3) (van Dokkum et al. 2004) K-band bright optically-selected galaxies (BX) (Shapley et al. 2004) BzK-selected starbursts (De Mello et al. 2004)
Very few observations
Emission line ratios and UV absorptions suggest solar to super-solar metallicities
Metallicity at z>3
Metal abundance derived from R23
1/10 < Z/Zsun < 1 (highly uncertain)
For the only certain galaxy: 1/6 < Z/Zsun < 1/2
Pettini et al. 2001
A cautionary tale…
[OII], Hβ, [OIII], Hα, [NII]Line ratios imply AGN and/or shock ionization (winds)
H-band spectrum only low metallicityK-band spectrum only high-metallicity
(van Dokkum et al. 2005)
z ~ 2.5 K-selected
The problem of “missing metals”
For a given IMF and a mean stellar yield (e.g. <y>=2.4%, Madau et al. 1996), the total amount of metals formed by a given time t is:
ρ(Z,t) = <y> ∫ dρ(stars,t)/dt
Only a fraction of the expected metals is actually seen in galaxies !
At z~2 : 5% DLAs 5% Submm galaxies 5% Distant Red Galaxies15% Optically-selected star-forming galaxies~30% (50-60% if corrected for incompleteness) (Bouché et al. 2006a, 2006b)
At z~3 the problem is even more serious :5-10% Lyman-break galaxies
The rest could be in hot phase with T~106 K (e.g. Ferrara, Scannapieco & Bergeron 2005)
Multi-wavelength surveys are needed to unveil diverse populations of high-z star-forming galaxies (but no Pop III objects detected yet)
The cosmic SFR density increases rapidly to z~1-2, but evolution unclear at z > 2
The old, massive, passive E/S0 galaxies already present at 1< z < 2 require star formation onset at z > 2-3 and short-lived powerful starbursts
Dusty, massive, high-metallicity starbursts at z~2-3: E/S0 progenitors ?
Mass is more important than environment in driving galaxy evolution
“Downsizing”: massive galaxies form stars earlier and faster
A mass-metallicity relation exists up to z ~ 2 (“downsizing” evolution)
Only a fraction of the expected metals is seen in galaxies
New generation of hierarchical merging models start to agree better with obs
The global picture