The cosmic evolution of star formation and metallicity

1. The cosmic evolution of star formation and metallicity over the last 13 billion years (an observational perspective) Andrea Cimatti (INAF - Osservatorio Astrofisico di Arcetri)

2. 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

3. The 1996+ revolution Keck HST ESO VLT JCMT

4. The “historical” Lilly – Madau plot Lilly et al. 1996 Madau et al. 1996

5. Star formation  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 past Large SSFR  significant mass is still building

6. The star formation that wesee: high-z galaxies which are forming stars

7. Optical selection based on broad-band colors Magenta (“BM” selection): 1.5 < z < 2 Cyan (“BX” selection): 2 < z < 2.5 Yellow+Green (LBG selection): z ~ 3 Steidel et al. 2005 BM BX LBG

8. Optically-selected star-forming galaxies at 1<z<4 Selected in the optical with the so called BM/BX/LBG color criteria (Steidel et al. 1996, Adelberger et al. 2004) < 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) (Shapley et al. 2003)

9. Photometric candidates at 7 < z < 10 HUDF data. Bouwens et al. 2004, 2005 No secure genuine “primordial” (Pop III) objects identified to date

10. K- to mm-selected dusty starbursts (1<z<5) Submm/mm galaxies K-selected starbursts E(B-V)>>0.3 < log M(stars,,gas)/(Msun) > ~ 11 SFR ~ 100-(1000) Msun/yr, Z ~ Zsun N ~ 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) … Spitzer IRAC-EROs Dusty EROs

11. 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 !?

12. Emission line galaxies Kurk et al. 2004 Lya at z=6.54 Lya at z=6.56 (Hu et al. 2002) 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. 2006

13. NEAR-IR SELECTION OPTICAL SELECTION

14. The star formation that we do not see: “fossil” galaxies which had star formation

15. Old passive spheroids at z>1 • E/S0 galaxies • Passively evolving • 1 < z < 2 • 1 – 4 Gyr old • M(stellar) > 1011 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

16. 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

17. Other massive galaxy candidates at 5 < z < 8 z J H K 3.6 4.5 5.8 8.0 24 micron STACKING (3”x3”) HST ACS: B+V+I+z K ≥ 25 (AB) Rodighiero et al. 2006

18. The cosmic evolution

19. The Lilly-Madau plot 10 years ago

20. The Lilly – Madau plot now Hatched and green: 24μm Red star: radio Blue: optical/UV DLAs Hopkins et al. 2005, 2006

21. Cosmic evolution from “archeology” of z~0 galaxies Heavens et al. 2004 SDSS data + MOPED

22. 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)

23. “Downsizing” (Cowie et al. 1996)

24. Dependence on mass and environment Thomas et al. 2004 Mass-dependent SFHs for z~0 galaxies (Heavens et al. 2004) Early-type galaxies 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) Constraints from σ, Hβ, Mgb, <Fe>, 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)

25. The evolution of the stellar mass function Largest sample analyzed to date: DEEP2 spectroscopy + optical-NIR SEDs >8000 galaxies over 1.5 square degrees (4 fields) 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 M(tr)

26. Specific star formation • 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 <SSFR> at z>2-3 for most massive galaxies  Downsizing of SF • See also Juneau et al. 2005, • Caputi et al. 2006 Feulner et al. 2005

27. Metallicity

28. 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. )

29. Emission line indicators Nagao et al. 2006

30. Stellar mass – ionized gas metallicity relation Tremonti et al. 2004 (SDSS)

31. Stellar vs. ionized gas metallicity Gallazzi et al. 2005 (SDSS)

32. Mass – metallicity relation at 0.4 < z < 1.0 A M-Z relation exists at <z>~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. 2005 (CFRS + GDDS samples)

33. Optically-selected star-forming galaxies at z~2 Shapley et al. 2004 Erb et al. 2006

34. Mass – metallicity relation at z~2 Erb et al. 2006 Optically-selected

35. 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

36. 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

37. 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

38. 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 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~106 K(e.g. Ferrara, Scannapieco & Bergeron 2005)

39. 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