How do galaxies accrete their mass? Quiescent and star - forming massive galaxies at high z

1. How do galaxies accrete their mass?Quiescent and star-forming massive galaxies at high z Paola Santini Osservatorio Astronomico di Roma Post-doc Roman Young Researchers Meeting 2009 July 21st Università “Tor Vergata”

2. Before starting…… Increase in the wavelength of e-m radiation received by a detector compared with the wavelength emitted by the source. Cosmological redshift is due to the expansion of the Universe: the distance between the emitting source and the observer increases while the light is propagating. REDSHIFT high z Universe = distant Universe = young Universe Recession velocity increases with distance (Hubble’s law) c is finite

3. The global picture of galaxy formation Hierarchical formation: massive galaxies were assembled recently from mergers of smaller subunits (smaller DM halos collapse earlier) supported by observations: e.g. ongoing star formation at low z, paucity of high mass galaxies at z >1 “ab initio” MODELS OF GALAXY FORMATION Kauffman et al. 93 ; Cole et al. 94; Somerville & Primack 00; Cole et al. 00; Menci et al. 02; Wu, Fabian, Nulsen 00, etc… Dynamical evolution of dark matter condensations

4. The different models differ in the description of the baryonic processes, especially the two main processes driving galaxy evolution: Gas uniformly distributed in the halo, star formation on a disk • star formation • conversion of gas into stars Gas distributed on filaments, disk fragments, star formation on blobs Dekel+09 Radio mode • suppression of star formation • most efficient: AGN feedback • introduced to reproduce passive galaxies at high z Quasar mode

5. z ≥ 2 : major phase in the assembly of massive galaxies Redshift 1) What drives the evolution of stellar mass at z ~ 2? (SF inside galaxies? Mergers?) 2) Quenching mechanisms? 3) Are these processes reproduced by the models? Searching observables which directly reflect these two processes M>7 1010 Mo Fontana+06

6. The GOODS-MUSIC sample Great Observatories Origins Deep Survey-MUltiwevelength Southern Infra-red Catalog (Grazian+06, Santini+09, http://lbc.oa-roma.inaf.it/goods) Photometry from 0.3 to 24 µm (15 bands) ~143 arcmin2CDF-South ~15000 objects z, Ks and 4.5 µm selected ~ 1800 spectroscopic z + well calibrated zphot U35 U38 (MPG/ESO-WFI) U VIMOS (VLT) B V i z (HST-ACS) J H Ks (VLT-ISAAC) 3.6 4.5 5.8 8.0 µm (Spitzer-IRAC) 24 µm (Spitzer-MIPS)

7. U 360nm B 420nm V 520nm R 650nm I 800nm J 1250nm K 2200nm Multiwavelengthsurveys SED fitting Multicolour surveys allow to estimate photometric redshifts and physical properties of each object of the catalog from the overall spectral shape Photometricz M(stars) SFR Dust Z

8. Dust emission Absorbed UV light PAH features Stellar emission MIPS 24 μm filter M82 (ISO) SFR estimate Future: Herschel SPIRE PACS 250, 350, 500mm 55  210 mm

9. Quiescent – star-forming selection Dusty star-forming 0.9 µm 2.2 µm 4.5 µm 24 µm Passively evolving Empirical UV-to-midIR SEDs (Polletta+07) 0.9 µm 2.2 µm 4.5 µm 24 µm

10. Quiescent galaxies

11. The very quiescent tail: Red&Dead galaxies 24 µm undetected galaxies Combined IR emission + SED fitting analysis SFR/M SFR/M < 10-11 yr-1 “RED&DEAD” galaxies SFR/M Fontana+09

12. The cosmic evolution of Red&Dead galaxies Galaxies with very low levels of SFR Time M>7 1010 Mo Fontana+09 • 20% of massive galaxies is already in a very quiescent phase at z~2-3 • Sensitive observable to constrain models: quenching mechanisms K07: Kitzbichler&White07 (Millennium Simulation) M06: Menci+06 F07: MORGANA (Monaco+07) N06: Nagamine+06

13. Star-forming galaxies

14. The Specific SFR — stellar mass relation What drives the evolution of stellar mass at z ~ 2? SFR/M Kitzbichler&White07 (Millennium Simulation) Total accreted mass = <SFR>active x <∆tactive phase> “Duty cycle” argument: 65% of M > 7 1010 Mo galaxies is actively SF-ing at 1.5<z<2.5, with <SFR>~300Mo/yr assuming that the active fraction is proportional to burst duration, the stellar mass acquired in this epoch is >1011Mo SFR=1000Moyr-1 At z ~ 2 massive galaxies are rapidly forming.The SFR directly observed in massive galaxies is enough to produce the bulk of the observed stellar mass density. Intense star formation processes within massive galaxies prevail over merging events at z ~ 2. 100Moyr-1 10Moyr-1 1Moyr-1 Santini+09

15. Comparison with theoretical predictions Menci+06 Modelsqualitatively reproduce the observations butunderestimate the SFR in massive galaxies MORGANA (Monaco+07) Kitzbichler&White07 (Millennium Simulation) Santini+09 (See also Daddi+07, Davé+08, Fontanot+09)

16. Summary & conclusions 1) The epoch z>~2 is a major phase in the assembly of massive galaxies 2) “Red&Dead” galaxies exist up to z=3 and most likely above: need for efficient feedback/quenching of SF mechanisms at high z 3) At z~2, more than 50% of massive galaxies are experiencing a major peak in their SFRH: during this process they accrete a substantial fraction of their mass (see also Daddi+07) 4) Theoretical models fail in predicting simultaneously the SFR (typically under-predicted) and the quenching of SF 5) Need for a different/new physics?