How do galaxies accrete their mass? Quiescent and star - forming massive galaxies at high z
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Transcript of How do galaxies accrete their mass? Quiescent and star - forming massive galaxies at high z
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
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
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
L
Empirical UV-to-midIR SEDs (Polletta+07)
Wavelength (µm)
70, 100, 160 m
PACS
MIPS 24 m
SPIRE250, 350, 500 m
@ z ~ 2
What will Herschel be able to observe?
above predicted 5 flux limit at 160m
above predicted 5 flux limit at 100m
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…