2012/02/24 by A. Cimatti, C. Nipoti, P. Cassata
Physics and Astronomy · #astro-ph.CO
paper · pdf · doi:10.1111/j.1745-3933.2012.01237.x
MNRAS (Letters), in press, 5 pages, 3 figures
arxiv created 2012/02/24 · arxiv updated 2015/06/04
We present the analysis of a large sample of early-type galaxies (ETGs) at 0<z<3 aimed at tracing the cosmic evolution of their size and compare it with a model of pure dissipationless (dry) merging in the LambdaCDM framework. The effective radius Re depends on stellar mass M as Re(M) ∝ Malpha with alpha ~ 0.5 at all redshifts. The redshift evolution of the mass- or SDSS-normalized size can be reproduced as ∝ (1+z)beta with beta ~ -1, with the most massive ETGs possibly showing the fastest evolutionary rate (beta ~ -1.4). This size evolution slows down significantly to beta ~ -0.6 if the ETGs at z>2 are removed from the sample, suggesting an accelerated increase of the typical sizes at z>2, especially for the ETGs with the largest masses. A pure dry merging LambdaCDM model is marginally consistent with the average size evolution at 0<z<1.7, but predicts descendants too compact for z>2 progenitor ETGs. This opens the crucial question on what physical mechanism can explain the accelerated evolution at z>2, or whether an unclear observational bias is partly responsible for that.