What can we learn from High-z Passive Galaxies ?

Andrea Cimatti

Università di Bologna – Dipartimento di Astronomia

Why Distant Early-type galaxies ?

z ≈ 0 z > 20<z<2

The link between ETGs at z ≈ 0 and their high-z progenitors

Dunlop et al. 1996, Spinrad et al. 1997A substantial populationof z>1 passive ETGsfound with NIR-selectedsurveys (e.g. K20, GDDS,MUNICS, FIRES, MUSYC,GOODS, COSMOS, …)

z=1.55age ≈ 3.5 Gyr

How many at z > 1 ?

Passive BzKs 1.4 < z < 2.5 (Kong et al. 2005)

DRG number density (z>2) (Marchesini et al. 2007)

Fraction of passive ETGs in a stellar mass-selectedcomplete sample (logM*>10.1 Msun) (GMASS Project; Cassata et al. 2008)

Stellar content and masses ?

Optical spectroscopy

Cimatti et al. 2008

Coadded spectrumof 13 ETGs at 1.3<z<2ESO VLT GMASS project

z ≈ 1.2 (Matsuoka et al. 2008)

z ≈ 2 (Kriek et al. 2007)

z ≈ 1.2 – 2 Longhetti et al. 2005

NIR spectroscopy

J H K

Constraints from spectral/SED analysis (0.5<z<2)

Stars : - 1 – 4 Gyr 1.5<z(form)<4 = f(mass) (downsizing) - τ ≈ 0.1 – 0.3 Gyr = f(mass) - Metallicity : Z ≈ 1 x Z(Sun) ?

Stellar masses : logMstars≈ 10.5 – 12 Msun (Chabrier IMF) (Mstars≈ Mdyn to z ≈ 1.2)

Dust extinction : AV ≈ 0

Δt(cluster – field) : ≈ 0 (≈1) Gyr for M>(M<)1011 Msun Consistent results with ETGs at z ≈ 0 and FP(z) to z ≈ 1 Cimatti et al. 2004-2008; Glazebrook et al. 2004; McCarthy et al. 2004; Daddi et al. 2005; Saracco et al. 2005; Treu et al. 2005, di Serego Alighieri et al. 2005, van der Wel et al. 2005, Longhetti et al. 2005, Kriek et al. 2006; Papovich et al. 2006, Matsuoka et al. 2008, Gobat et al. 2008; Rettura et al. 2008, Bernardi et al. 1998 – 2007, Heavens et al. 2004, Kuntschner et al. 2002; Thomas et al. 2005, Jimenez et al. 2007 … + MANY OTHERS

Cosmology with ETGs ?

dz/dt Dark Energy EOS (w)

N≈105

407.0608.0721.0

w

Moresco et al. 2009

(Jimenez & Loeb 2002; Jimenez et al. 2003)

Early-type galaxies at z > 3 ?

Typically :3 < z < 7(?)10.8 < log M* < 11.5 Msun Ages ~ 0.2 – 0.8 Gyr AV ~ 0 – 1

Mobasher et al. 2005Dunlop et al. 2006Brammer et al. 2006Rodighiero et al. 2007Wiklind et al. 2007Mancini et al. 2008

Example of a high-z ETG photometric candidate (Mancini et al. 2008)

Internal Structure Evolution ?

- ETGs at z>1 are ≈2-3x smaller and ≈10-30x denser than at z ≈ 0 - How do high-z ETG increase their size to z ≈ 0 ? Dry merging ?- Only SMGs at z>2 have similar densities (evolutionary link ?)- Or … are the small sizes due to an observational bias ? (Mancini et al. 2009)

1.3 < z < 2.5

Cimatti et al. 2008

van der Wel et al. 2008

The size / density problem

12 “secure” pBzK with K<17.7 (Vega) – SSP SEDs, no MIPS1.2 < z(phot) < 2, M>1011 Msun (Chabrier IMF, M05)

High concentration + largelow surface brightness halo

Are ETGs at z>1 really small ?

Mancini et al. 2009

80% have Re ≈ 5 – 11 kpc, n ≈ 2 – 8 Most of them follow the local n – Re relation Lower masses lower SNR Missing the faint halos ?

COSMOS

HST+ACS (I-band)

Internal velocity dispersion of ETGs at z > 1.4

Work in progress …(AC, Cappellari, di Serego Alighieri et al.)

observed template

If the superdense ETGs have the samedynamical structure of z=0 ETGs andbelong to the same homologous family,given their M* and Re, we expect highvelocity dispersions σvel

Where do they live ?

1.600 < z < 1.622

N = 42

Overdensity : 6 ± 3

σ ≈ 450 km s-1

If relaxed : R200 = 0.5 Mpc Mvir = 9 x 1013 Msun

Overdensity and volume (Steidel et al. 1998 method) :

M ≈ 5 x 1013 Msun (lower limit : only a fractionof the structure falls in the GMASS field)

z = 1.61

Main features :

- z > z(highest-z clusters)

- it contains ETGs (vs LBG and LAE overdensities)

- 3 ETGs within 100 kpc : dry merging ? (comparewith z=1.5 structure of McCarthy et a. 2007)

- Irregular/filamentary : not yet relaxed

- No diffuse X-rays : LX < 3 x 1043 erg s-1

Are we witnessing the assembly of a cluster ?

1 Mpc

Galaxy properties:

- more ETGs

- redder

- 2x older galaxies

- more massive

- lower SFR and SSFR

than in the “field” at 1.4<z<1.8

Two slides for the discussion time …

Massive thick disk Gas-rich major merger

Powerful starburst (e.g. SMGs at z≈2-4)

Smooth accretion

Feedback (AGN ?)

Star formation quenching

Superdense compact remnant (z ≈ 1-2)

Size growth (minor and/or major, wet and/or dry merging, smooth accretion)

Massive ETGs reach most of completion at z ≈ 0.7

Gas exhaustion ?

?

Believable Results

Massive ETGs (M > 1011 Msun) mostly assembled at z ~ 0.7 Lower mass ETGs continue to assemble at 0 < z < 0.7 (downsizing) The Fundamental Plane to z ≈ 1 shows a mass-dependent evolution The bulk of stars is old, formed in short-lived bursts at z > 2 Spectroscopically identified old/massive ETGs exist up to z ~ 2.5

Open Questions

ETG evolution at z > 1 : N(z), luminosity and mass functions Stellar metallicity and metallicity evolution Small sizes at z > 1, dynamical masses, σvel, and growth mechanism Physics of ETG formation, feedback and mass assembly Old/massive ETG photometric candidates at z>3 Comparison with model predictions