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What can we learn from High-z Passive Galaxies ?

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.

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What can we learn from High-z Passive Galaxies ?

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  1. What can we learn from High-z Passive Galaxies ? Andrea Cimatti Università di Bologna – Dipartimento di Astronomia

  2. Why Distant Early-type galaxies ? z ≈ 0 z > 2 0<z<2 The link between ETGs at z ≈ 0 and their high-z progenitors

  3. Dunlop et al. 1996, Spinrad et al. 1997 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

  4. How many at z > 1 ?

  5. 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)

  6. Stellar content and masses ?

  7. Optical spectroscopy Coadded spectrum of 13 ETGs at 1.3<z<2 ESO VLT GMASS project Cimatti et al. 2008

  8. NIR spectroscopy z ≈ 1.2 (Matsuoka et al. 2008) J H K z ≈ 2 (Kriek et al. 2007) z ≈ 1.2 – 2 Longhetti et al. 2005

  9. 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

  10. Cosmology with ETGs ?

  11. dz/dt Dark Energy EOS (w) (Jimenez & Loeb 2002; Jimenez et al. 2003) Moresco et al. 2009 N≈105

  12. Early-type galaxies at z > 3 ?

  13. Example of a high-z ETG photometric candidate (Mancini et al. 2008) Typically : 3 < z < 7(?) 10.8 < log M* < 11.5 Msun Ages ~ 0.2 – 0.8 Gyr AV ~ 0 – 1 Mobasher et al. 2005 Dunlop et al. 2006 Brammer et al. 2006 Rodighiero et al. 2007 Wiklind et al. 2007 Mancini et al. 2008

  14. Internal Structure Evolution ?

  15. The size / density problem - 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 van der Wel et al. 2008 Cimatti et al. 2008

  16. Are ETGs at z>1 really small ? Mancini et al. 2009 COSMOS 12 “secure” pBzK with K<17.7 (Vega) – SSP SEDs, no MIPS 1.2 < z(phot) < 2, M>1011 Msun (Chabrier IMF, M05) HST+ACS (I-band)  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 ? High concentration + large low surface brightness halo

  17. Internal velocity dispersion of ETGs at z > 1.4 observed template Work in progress … (AC, Cappellari, di Serego Alighieri et al.) If the superdense ETGs have the same dynamical structure of z=0 ETGs and belong to the same homologous family, given their M* and Re, we expect high velocity dispersions σvel

  18. Where do they live ?

  19. 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

  20. 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 : LX < 3 x 1043 erg s-1 Are we witnessing the assembly of a cluster ? 1 Mpc

  21. Galaxy properties: - more ETGs - redder - 2x older galaxies - more massive - lower SFR and SSFR than in the “field” at 1.4<z<1.8

  22. Two slides for the discussion time …

  23. Gas-rich major merger Massive thick disk Powerful starburst (e.g. SMGs at z≈2-4) Smooth accretion Feedback (AGN ?) Gas exhaustion ? 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

  24. 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

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