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Galaxy Surveys @ OABo

Galaxy Surveys @ OABo. VVDS “ The Galaxy Mass Assembly History ”. Lucia Pozzetti INAF Osservatorio Astronomico di Bologna. Galaxy Formation and Evolution. Λ CDM Hierarchical structure formation Semi-analytical predicts up-sizing formation. Observations:

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Galaxy Surveys @ OABo

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  1. Galaxy Surveys @ OABo VVDS “The Galaxy Mass Assembly History” Lucia Pozzetti INAF Osservatorio Astronomico di Bologna

  2. Galaxy Formation and Evolution • ΛCDM Hierarchical structure formation Semi-analytical predicts up-sizing formation Observations: Evolution driven by the final stellar mass, with massive galaxies formed earlier and faster than low-mass galaxies (downsizing). Match theory and observations + Role of the mass and enviroment ?

  3. 2MASS + 2dFGRS : Near-infrared LF (J,Ks)(Cole et al. 2001) yielding the stellar mass function of galaxies Local Luminosity and Mass Functions: 2MASS 2MASS + SDSS :red/ETGs galaxies dominate the luminous/massive part of LF/MF (Kochaneck et al 01, Bell et al. 03)

  4. Constraints from present-day early-type galaxies Constraints on age/SFH from σ, Hβ, Mgb, <Fe>, stellar populations Thomas et al. 2005 See also: Bernardi et al. 98,03-04 Kuntschner et al. 02 Pipino & Matteucci 2004 +MANY others….. See Schiavon et al. 2006 for a different view… =>More massive spheroids form earlier and faster • Formation time scales is independent of environment • BUT ~1-2 Gyr younger in low density environments ? • Not in all studies (Thomas et al. 2007, Schiavon et al. 2006) => Mass assembly almost completed around z~1

  5. RESULTS from VVDS: (PI Le Fevre) DEEP:17.5<IAB<24,0.5 deg²(10k zspec) WIDE:17.5<IAB<22.5,10deg² Ultra-Deep:22.5<IAB<24.75,600 arcmin² + multi-band photometry: GALEX to SPITZER + VLA (>80 Jy) RESULTS ON THE MASS ASSEMBLY: • Global MF evolution (Pozzetti et al. 2007) • Build up of the red sequence (Arnouts et al. 2007) • Mass assembly (Vergani et al. 2008) • Star formation as driver of mass growth (Walcher et al. 2008) • Merger rate (De Ravel et al. 2009)

  6. Low-mass end of the MF I-andK- selected Mass function: Pozzetti, et al., 2007: Complete up to logM=10 at z=1 I-selected Complete up to logM=10.3 at z=2 in K-selected Substantial population of low mass galaxies SDSS: Baldry et al. 2008

  7. Mass assembly downsizing I-andK- selected Mass function: Pozzetti, et al., 2007 mass-dependent evolution of the number/mass density: Massive tail is present up to z=1. Continuous evolution for intermediate/low-mass galaxies Mass assembly is earlier in more massive galaxies in contrast with hierarchical models Most of massive galaxies are in place up to z=1, less massive galaxies have assembled their mass later and continuously

  8. Evolution by types MDs by colors:Red vs. Blue Arnouts et al. 2007 High mass growth rate for ETGs Blue population remain almost unchanged Coincidence of colour and photometric transformation ??

  9. Evolution of active/passive galaxies Vergani et al. 2008 MF by spectral types: ETGs vs. LTGs Intermediate-mass RED population increase with cosmic time Blue population decrease in fraction but remain almost unchanged in density we witness an increasing abundance of massive spectroscopically early-type systems at the expense of the late-type systems.

  10. Mass growth Walcher et al. 2008 Assuming a mass growth due to SFHs the predicted MF roughly agrees with the observed one The role of major merging events seems to be only marginal at z < 1.3

  11. Merging Rate Pair fraction dMB<1.5 dv<500 km/s dr<20-100 kpc De Ravel et al. 2008 Late-type mergers were more frequent in the past early-type mergers are more frequent today Merger rate decrease with cosmic time and mass 20% mass growth in present-day galaxies with logM>9.5

  12. MFs: Millenium-StellarMass,VVDS-I-selected, VVDS-K-selected Dotted line: local MFs.(Cole et al. 2001, Bell et al. 03) Dashed lines: limit due to I<24 HM Millenium Stellar Mass Function LP (old results…) Comparison with Millennium:  excess of intermediate/low-Mass galaxies(logM<10) galaxies compared to VVDS Lack of high-z massive galaxies z>1.6 Faster evolution in Millenium compared to VVDS at all masses

  13. Highlights & global picture • Redshift = 0.1-1.2 • Mass-assembly downsizing: • Mass dependent MF evolution: Massive galaxies were in place already at z~1, low-mass galaxies increase in number densities with cosmic time low/intermediate mass early types(ETGs) increase with cosmic time Star forming galaxies (LTGs) decrease in fraction but remain almost unchanged in mass density. Mass growth due to SF can account for MF evolution • Major Merger rate contribute only to 20% mass growth in present-day galaxies with logM>9.5 • Transformation from active to passive with cosmic time (major merger only marginal) • Hierarchical models : • Overpredict low-Luminosity/Masses galaxies at all redshifts • Underpredict high-Mass galaxies at z>1.6 • Faster evolution compared to VVDS at all masses

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