Recent Structural Evolution of Early‐Type Galaxies: Size Growth fromz= 1 toz= 0

Abstract

Strong size and internal density evolution of early-type galaxies between z $ 2 and the present has been reported by several authors. Here we analyze samples of nearby and distant (z $ 1) galaxies with dynamically measured masses in order to confirm the previous, model-dependent results and constrain the uncertainties that may play a role. Velocity dispersion () measurements are taken from the literature for 50 morphologically selected 0:8 < z < 1:2 field and cluster early-type galaxies with typical masses M dyn ¼ 2 ; 10 11 M . Sizes (R eA ) are determined with Advanced Camera for Surveys imaging. We compare the distant sample with a large sample of nearby (0:04 < z < 0:08) early-type galaxies extracted from the Sloan Digital Sky Survey for which we determine sizes, masses, and densities in a consistent manner, using simulations to quantify systematic differences between the size measurements of nearby and distant galaxies. We find a highly significant difference between the -R eA distributions of the nearby and distant samples, regardless of sample selection effects. The implied evolution in R eA at fixed mass between z ¼ 1 and the present is a factor of 1:97 AE 0:15. This is in qualitative agreement with semianalytic models; however, the observed evolution is much faster than the predicted evolution. Our results reinforce and are quantitatively consistent with previous, photometric studies that found size evolution of up to a factor of 5 since z $ 2. A combination of structural evolution of individual galaxies through the accretion of companions and the continuous formation of early-type galaxies through increasingly gas-poor mergers is one plausible explanation of the observations.

From magnitudes and redshifts of supernovae, their light-curves, and angular sizes of galaxies to a tenable cosmology

“…Van der Wel et al (2008) compared morphologically selected galaxies at z = 1±0.2 with a sample at z = 0.06±0.02. They found significant size evolution by a factor of two.…”

Dry Mergers and the Formation of Early-Type Galaxies: Constraints From Lensing and Dynamics

“…However, higher-z early-type galaxies must not necessarily obey the z = 0 lensing scaling laws. In fact, though the lensing scaling relations at higher redshift are not available, measures of the effective radii and the stellar masses of highredshift (z 1-2) early-type galaxies suggest that these objects may be remarkably more compact than their local counterparts (e.g., Daddi et al 2005;Trujillo et al 2006;Zirm et al 2007;Cimatti et al 2008;van Dokkum et al 2008;van der Wel et al 2008). As shown by our current results, as well as previous work (Nipoti et al 2003a;Boylan-Kolchin et al 2006), dry merging has the effect of making galaxies less compact, so it has been proposed that evolution of early-type galaxies through such a mechanism might be consistent with the recent observational finding that higher-z galaxies are more compact (e.g., Khochfar & Silk 2006;Hopkins et al 2009a;van der Wel et al 2009).…”

The Stellar Halos of Massive Elliptical Galaxies. Ii. Detailed Abundance Ratios at Large Radius

“…A full census of the metallicity and abundance ratio content of elliptical galaxies requires spatially resolved observations. The recent discovery of dramatic (factor of 2-4) size growth in elliptical galaxies from z ≈ 2 to the present (e.g., Daddi et al 2005;Trujillo et al 2006;van Dokkum et al 2008;van der Wel et al 2008;Cimatti et al 2008;Damjanov et al 2009;Williams et al 2010;Cassata et al 2010) is now supported by an increasing number of dynamical studies (Cappellari et al 2009;van de Sande et al 2011). It seems that much of the late-time growth of elliptical galaxies has occurred in their outer parts (e.g., Naab et al 2009;van Dokkum et al 2010).…”