How do galaxies accrete How do galaxies accrete their mass?their mass?

Quiescent and starQuiescent and star--forming massive forming massive galaxies at high zgalaxies at high z

Paola Paola SantiniSantini

THE ORIGIN OF GALAXIES: LESSONS FROM THE DISTANT UNIVERSEObergurgl, 12-17 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 processesFontana+0

6

Redshift

M>7 1010 Mo

The GOODS-MUSIC sample

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)

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 arcmin2 CDF-South ~ 15000 objects z, Ks and 4.5 µm selected~ 1800 spectroscopic z + well calibrated zphot

24 µm (Spitzer-MIPS)

Empirical UV-to-midIR SEDs (Polletta+07)

24 µm

24 µm

4.5 µm2.2 µm0.9 µm

4.5 µm2.2 µm0.9 µm

Dusty star-forming

Passively evolving

F(24μm)/F(K) as SED

indicator

Mid-IR emission of quiescent and active galaxies

F(24

)/F(

K)

(UAB-V)

N

Quiescent galaxies

The very quiescent tail: Red&Dead galaxies

SFR/M

SFR/M

SFR/M < 10-11

yr-1

“RED&DEAD”

galaxies

24 µm undetected

galaxies

Combined IR emission + SED fitting analysis

Fontana+09

M>7 1010 Mo

• 15-20% 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+06F07: MORGANA (Monaco+07)N06: Nagamine+06

The cosmic evolution of Red&Dead galaxiesGalaxies with very low levels of SFR

Fontana+09

M>7 1010 Mo

Star-forming galaxies

PAH featuresStellar

emission

Absorbed UV light

Dust emission

24 μm filter

M82 (ISO)

SFR estimate

SFR Dust

Z

M(stars)

Photometric z

SED fitting to the SED fitting to the multiwavelength multiwavelength

photometryphotometry

SFR(Moyr-1) = 1.8 x 10-

10 x Lbol (Kennicutt98)

(from Dale&Helou02 templates)

where Lbol = (2.2 x LUV + LIR),

LUV = 1.5 x L2700Å, 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 < 0.6

0.6 < z < 1.0

1.0 < z < 1.5

1.5 < z < 2.5

Highly obscured AGN candidates

(Fiore+08)

GOODS-S

+

GOODS-N

SFR/MThe Specific SFR — stellar mass relation

Kitzbichler&White07

(Millennium Simulation)

Santini+09

What drives the evolution of stellar mass at z ~ 2 ?

Total accreted mass = <SFR>active x

<∆t active 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

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 Moyr -1

100 Moyr -1

10 M

oyr -1

1 Moyr -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

SPIRE250, 350, 500 m

@ 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 160m

above predicted 5 flux limit at 100m

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 z3) 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…