How do galaxies accrete their mass? Quiescent and star - forming massive galaxies at high z Paola Santini THE ORIGIN OF GALAXIES: LESSONS FROM THE DISTANT UNIVERSE Obergurgl, December 2009 Osservatorio Astronomico di Roma

z ≥ 2 : major phase in the assembly of massive galaxies 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 Fontana+06 Redshift M> M o

The GOODS - MUSIC sample U35 U38 (MPG/ESO-WFI) U VIMOS (VLT) B V i z (HST - ACS) J H Ks (VLT - ISAAC) µm (Spitzer - IRAC) Great Observatories Origins Deep Survey - MUltiwevelength Southern Infra - red Catalog (Grazian+06, Santini+09, Photometry from 0.3 to 24 µm (15 bands) ~ 143 arcmin 2 CDF-South ~ objects z, K s and 4.5 µm selected ~ 1800 spectroscopic z + well calibrated zphot 24 µm (Spitzer - MIPS)

Empirical UV - to - midIR SEDs (Polletta+07) 24 µm 4.5 µm2.2 µm0.9 µm 4.5 µm2.2 µm0.9 µm Dusty star - forming Passively evolving F(24 μ m)/F(K) as SED indicator Mid - IR emission of quiescent and active galaxies

F(24)/F(K) (U AB -V) N

Quiescent galaxies

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

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

Star - forming galaxies

PAH features Stellar emission Absorbed UV light Dust emission 24 μ m filter M82 (ISO) SFR estimate SFR Dust Z M(stars) Photometric z SED fitting to the multiwavelength photometry SFR(M o yr - 1 ) = 1.8 x x L bol (Kennicutt98) (from Dale&Helou02 templates) where L bol = (2.2 x L UV + L IR ), L UV = 1.5 x L 2700Å, uncorrected for extinction (Papovich+07)

Comparison between SFR estimators GOODS - South + GOODS - North (by Stefano Berta) Systematic trend: open issue… (see later) 0.3 < z < < z < < z < < z < 2.5 Highly obscured AGN candidates (Fiore+08)

GOODS - S + GOODS - N SFR/M The Specific SFR — stellar mass relation Kitzbichler&White07 (Millennium Simulation) Santini+09 What drives the evolution of stellar mass at z ~ 2 ? Total accreted mass = active x “Duty cycle” argument: 65% of M > M o galaxies is actively SF - ing at 1.5 ~ 300M o /yr assuming that the active fraction is proportional to burst duration, the stellar mass acquired in this epoch is >10 11 M o 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. SFR=1000 M o yr M o yr M o yr M o yr - 1

How can future data help us? Herschel

L Empirical UV - to - midIR SEDs (Polletta+07) Wavelength (µm) 70, 100, 160  m PACS MIPS 24  m SPIRE 250, 350, 500  z ~ 2

DH: Dale&Helou02 CE: Chary&Elbaz01 Systematics in IR templates

What will Herschel be able to observe? above predicted 5  flux limit at 160  m above predicted 5  flux limit at 100  m

PACS Evolutionary Probe (Herschel GT program) Rodighiero et al, in preparation

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 mechanisms of SF 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) Summary & conclusions 5) Need for a different/new physics? (e.g. cooling flows – Dekel+06,08,09) 4) Theoretical models fail in predicting simultaneously the SFR (typically under - predicted) and the quenching of SF 6) Waiting for new Herschel data…