Page 1 Hot topics on Galaxy Formation and Evolution 3. Archeology and Size Evolution Roberto Saglia Max-Planck Institut für extraterrestrische Physik Garching, Germany Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 2 Outline • Constraints on formation epochs of local early-type galaxies: galaxy archeology • Constraints from redshift evolution • Size evolution of galaxies • Constraints on the IMF Padova, March 2012 Hot topics on galaxy formation and evolution 3
Ages and Page 3 < > H β Lick indices Mg , Fe , b to break the age-metallicity metallicities degeneracy Z = [ ] 0.02 = − Z H / log( / Z H ) log( / Z H ) e e Trager et al. 2000 AJ, 120, 165 Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 4 Galaxy archeology Thomas et al. 2005, ApJ, 621, 673 Red: Es, Blue:S0, Green: cD Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 5 Element abundances in solar neighbourhood: [ α /O] = logarithm of the ratio of density of alpha elements (Mg, Si, Ca, Ti) and density of Fe relative to this ratio in the sun: ρ ρ / α = α [ / Fe ] log Fe ρ ρ / α e e , Fe , see: Wheeler et al. ARAA 27 (1989) Padova, March 2012 Hot topics on galaxy formation and evolution 3
Enrichment through Page 6 Mg/Fe Supernovae of Type II overabundance α − elements(O, Mg, Ca...) enhanced with respect to Fe Only short (<1Gyr) time scales for the star formation are allowed. Type I SNs produce Fe to solar values Hierarchical galaxy formation problematic? Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 7 The epoch and duration of formation of Es Big (local) ellipticals formed their stars early and quickly. Small ellipticals formed their stars more recently and with more extended periods of star formation. Formation in low density environments happens with some delay. Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 8 The formation epoch of dark halos Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 9 The Fundamental Plane of Elliptical Galaxies A comprehensive set of global parameters of elliptical galaxies is: � The half light (or effective) radius r e � The mean surface brightness I e (or Σ e ) within r e � The central velocity dispersion σ 0 � The luminosity L � The mass M The following two relations relate these quantities: L / 2 (Definition of mean surface brightness within r ) Σ = e e π 2 r e M = σ 2 c (Virial equilibrium) 0 r e with the structure parameter c which contains all unknown details about the galaxies ’ structure. Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 10 Multiplication yields an expected relation for these parameters: − 1 ⎛ ⎞⎛ ⎞ c M − = σ Σ 2 1 r ⎜ ⎟⎜ ⎟ e π 0 e ⎝ 2 ⎠⎝ L ⎠ Because neither M/L or c are expected to vary very much, the brackets are nearly constant and imply that ellipticals should define a plane-like distribution in the 3-space of their global parameters (r e , Σ e , σ 0 2 ). Astonishingly, this plane is much better defined than naively expected, with very low dispersion perpendicular to the plane (implying a variance in the product of the brackets less than 10%) and a small but significant tilt (implying small but significant changes in the structure of ellipticals as a function of their luminosity or mass), see Djorgovski & Davis 1987, Dressler et al. 1987. The observed so-called ” fundamental plane ” relation reads: ∝ σ Σ − 1.4 0.85 r e 0 e This is consistent with the virial expectation, if π ⎛ ⎞⎛ ⎞ ∝ 2 M ∝ 0.2 0.25 M L ⎜ ⎟⎜ ⎟ ⎝ c ⎠⎝ L ⎠ Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 11 Ellipticals and bulges lie in a ‘fundamental plane’ è at a given mass, their M/L shows only <15% scatter è they have homogenous, mostly old stellar populations Dressler et al. 1987, Djorgovski & Davis 1987, Bender, Burstein & Faber 1992,1994 Padova, March 2012 Hot topics on galaxy formation and evolution 3
Sersic profiles Page 12 Giant ellipticals are described by the de Vaucouleurs profile: ( ) 1 4 − = 7.67 r r I(r) I(0) e e More generalized profile: ( ) 1 n − = b r r I(r) I(0) e n e Kormendy et al. 2009, ApJSS, 182, 216-209 There exists a puzzling correlation of Sersic n with galaxy luminosity. Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 13 Bulge+Disk fits • Fit 2-dimensional image using GIM2D or GALFIT Simard et al. 2011, ApJSS, 196, 11 • Use Sersic profiles or 1.12 millions SDSS Exponential+De Vaucouleurs galaxies (disk+bulge) profiles Padova, March 2012 Hot topics on galaxy formation and evolution 3
How to compute Page 14 galaxy sizes = + R ( a b )/ 2 ave e e = 1/ 2 R ( a b ) har e e Padova, March 2012 Hot topics on galaxy formation and evolution 3
The ESO Distant Cluster Survey Page 15 (EDisCS) Study evolution of cluster galaxies and clusters in 20 fields with clusters at z=0.4 – 1.0 P.I. S. White ( MPA-Garching, D ) H. Rottgering ( Leiden, NL ) A. Aragón-Salamanca ( Nottingham, UK ) P. Schneider ( Bonn, D ) R. Bender ( Munich, D ) D. Zaritsky ( U. Arizona, USA ) P. Best ( ROE, Scotland ) M. Dantel ( OPM, F ) M. Bremer ( Bristol, UK ) G. De Lucia ( MPA, D ) S. Charlot ( MPA, D & IAP, F ) V. Desai ( U. Washington, USA ) D. Clowe ( Bonn, D) C. Halliday ( Padova, I ) J. Dalcanton ( U.Washington, USA ) B. Milvang-Jensen ( MPE, D ) B. Fort ( IAP, F ) S. Poirier ( OPM, F ) P. Jablonka ( OPM, F ) G. Rudnick ( MPA, D ) G. Kauffmann ( MPA, D ) R. Saglia (MPE, D ) L. Simard ( U. Victoria, C ) Y. Mellier ( IAP, F ) R. Pello ( OMP, F ) J. Varela ( Padova, I) B. Poggianti ( Padova, I ) Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 16 THE DATASET • Deep imaging: VRIJK at z~0.8, BVIK at z~0.5 (FORS2/VLT + SOFI/NTT) (White et al. 2005) • HST/ACS imaging for 10 most distant clusters (80 orbits, Desai et al. 2007). Re from GIM2D • WFI/2.2m RVI imaging for all 20 fields • XMM data for >=3 clusters (Johnson et al. 2006) • Spectroscopy: at least 4 FORS2 masks/cluster at long exposure to get spectra to I~23 (z~0.8) or 22 (z~0.5) (Halliday et al. 2004, Milvang-Jensen et al. 2008). s measured using pPXF for spectroscopic early-type Padova, March 2012 Hot topics on galaxy formation and evolution 3
The EDISCS FP with HST Page 17 Padova, March 2012 Hot topics on galaxy formation and evolution 3
M/L Evolution is 'passive' Page 18 Δ = log M / L Δ 2 ZP β 5 Z(formation)=2 Salpeter IMF, solar metallicity Field Galaxies have a Z(formation)=3.5 lower Z Salpeter IMF, half formation solar metallicity Z(formation)=1.5 Salpeter IMF, Twice Solar metallicity Padova, March 2012 Hot topics on galaxy formation and evolution 3
Mass evolution Page 19 Lower-mass ellipticals evolve quicker Lower formation redshift ... but selection effects are nasty. Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 20 Constraints on the IMF At z~0 the light of 12 Gyr stars is dominated by solar mass stars, at z~1.4 by stars 1.4 times more massive. A flatter IMF evolves faster b than Salpeter The formation redshift has to be higher to match the data b Renzini 2005, Ap.Sp.Sci. 327,221 Padova, March 2012 Hot topics on galaxy formation and evolution 3
Page 21 The cosmic evolution and the IMF A flat-top IMF has a large number of short-lived stars à more rapid luminosity evolution. A flat-top IMF reduces the number of turn-off stars with respect to more luminous red giants à weaker color evolution Combination of color and FP Van Dokkum 2008, ApJ, 674, 29 Evolution can constrain the IMF Padova, March 2012 Hot topics on galaxy formation and evolution 3
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