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 indicators High-z star-forming galaxies “Fossil” galaxies Cosmic evolution of SF density Cosmic evolution of stellar mass “Downsizing” Metallicity indicators Metallicity of high-z galaxies Cosmic evolution of the mass-metallicity relation

The revolution HST ESO VLTJCMT Keck

The “historical” Lilly – Madau plot Lilly et al 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 ( Å) L(FIR) (and L(MIR) ?) ( μm) 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 past Large 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 Magenta (“BM” selection): 1.5 < z < 2 Cyan (“BX” selection): 2 < z < 2.5 Yellow+Green (LBG selection): z ~ 3 BM BX LBG

Optically-selected star-forming galaxies at 1<z<4 (Shapley et al. 2003) = 10.3 ± 0.5 = 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 ~ 11 SFR ~ 100-(1000) Msun/yr, Z ~ Zsun N ~ 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) Spitzer IRAC-EROs Submm/mm galaxies K-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 consistent with mass of ~ several x 1e8 Msun and molecular gas with mass of the order of 1e10 Msun SFR > 1000 Msun/yr !?

Emission line galaxies Line emitting galaxies are generally found 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., Taniguchi et al. 2005, Bunker et al., Doherty et al Lya at z=6.56 (Hu et al. 2002) Kurk et al 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 galaxies Passively evolving 1 < z < 2 1 – 4 Gyr old M(stellar) > Msun  Problem for galaxy formation models z(SF onset) > 2 – 3 Short-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 micron HST ACS: B+V+I+z K ≥ 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: 24μm Red star: radio Blue: optical/UV DLAs

Cosmic evolution from “archeology” of z~0 galaxies Heavens et al 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 density L<L* galaxies are the dominant sites of star formation SFR 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 Constraints from σ, Hβ, Mgb,, stellar populations More massive spheroids form earlier and faster Formation time scales independent of environment ~1-2 Gyr younger in low density environments Mass 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 massive galaxies which dominated cosmic SF at z~3 are in clusters today, whereas galaxies 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 per galaxy 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 blue galaxy 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 SSFR = SFR/M(stars)  Higher in lower mass galaxies at all redshifts  Oldest stars in largest mass galaxies  Massive galaxies are in a quiescent state at z<2 (no significant change in stellar mass)  Strong increase of 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 R 23 = ([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) R 23 + [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 Å (e.g. Savaglio et al. 2004) UV absorption features (e.g Å, 1425 Å, 1978 Å, Rix et al. 2004) Metal absorption lines in DLAs (e.g. Pettini et al. )

Nagao et al Emission line indicators

Stellar mass – ionized gas metallicity relation Tremonti et al (SDSS)

Stellar vs. ionized gas metallicity Gallazzi et al (SDSS)

Mass – metallicity relation at 0.4 < z < 1.0 A M-Z relation exists at ~0.7 and evolves with redshift At a given mass, a galaxy at z~0.7 has lower metallicity vs. z~0 Evolution 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 (CFRS + GDDS samples)

Optically-selected star-forming galaxies at z~2 Shapley et al Erb et al. 2006

Mass – metallicity relation at z~2 Erb et al Optically-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 R 23 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 metallicity K-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. =2.4%, Madau et al. 1996), the total amount of metals formed by a given time t is: ρ(Z,t) = ∫ 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 Galaxies 15% 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~10 6 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 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