The cosmic evolution of star formation and metallicity
description
Transcript of The cosmic evolution of star formation and metallicity
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