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 > 2 0<z<2 The link between ETGs at z ≈ 0 and their high-z progenitors

Dunlop et al. 1996, Spinrad et al A substantial population of z>1 passive ETGs found with NIR-selected surveys (e.g. K20, GDDS, MUNICS, FIRES, MUSYC, GOODS, COSMOS, …) z=1.55 age ≈ 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-selected complete sample (logM*>10.1 Msun) (GMASS Project; Cassata et al. 2008)

Stellar content and masses ?

Optical spectroscopy Cimatti et al Coadded spectrum of 13 ETGs at 1.3<z<2 ESO VLT GMASS project

z ≈ 1.2 (Matsuoka et al. 2008) z ≈ 2 (Kriek et al. 2007) z ≈ 1.2 – 2 Longhetti et al 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 : logM stars ≈ 10.5 – 12 Msun (Chabrier IMF) (M stars ≈ M dyn to z ≈ 1.2)  Dust extinction : A V ≈ 0  Δt(cluster – field) : ≈ 0 (≈1) Gyr for M>(M<)10 11 Msun  Consistent results with ETGs at z ≈ 0 and FP(z) to z ≈ 1 Cimatti et al ; 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 – 2007, Heavens et al. 2004, Kuntschner et al. 2002; Thomas et al. 2005, Jimenez et al … + MANY OTHERS

Cosmology with ETGs ?

dz/dt  Dark Energy EOS (w) N≈10 5 Moresco et al (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 A V ~ 0 – 1 Mobasher et al Dunlop et al Brammer et al Rodighiero et al Wiklind et al Mancini et al 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 van der Wel et al The size / density problem

12 “secure” pBzK with K<17.7 (Vega) – SSP SEDs, no MIPS Msun (Chabrier IMF, M05) High concentration + large low surface brightness halo Are ETGs at z>1 really small ? Mancini et al  80% have R e ≈ 5 – 11 kpc, n ≈ 2 – 8  Most of them follow the local n – R e 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 same dynamical structure of z=0 ETGs and belong to the same homologous family, given their M * and R e, we expect high velocity dispersions σ vel

Where do they live ?

1.600 < z < N = 42 Overdensity : 6 ± 3 σ ≈ 450 km s -1 If relaxed : R 200 = 0.5 Mpc M vir = 9 x Msun Overdensity and volume (Steidel et al method) : M ≈ 5 x 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 ? (compare with z=1.5 structure of McCarthy et a. 2007) - Irregular/filamentary : not yet relaxed - No diffuse X-rays : L X < 3 x 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 > 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, σ vel, and growth mechanism  Physics of ETG formation, feedback and mass assembly  Old/massive ETG photometric candidates at z>3  Comparison with model predictions