Size and velocity-dispersion evolution of early-type galaxies in a Lambda cold dark matter universe

Details Size and velocity-dispersion evolution of early-type galaxies in a Lambda cold dark matter universe Size and velocity-dispersion evolution of early-type galaxies in a Lambda cold dark matter universe

2012-02-05

arxiv.org/abs/1202.0971v3

Astronomy and Astrophysics

Astrophysics

Galaxy Astrophysics

20 pages, 14 figures, matching version published in MNRAS. Corrected plots in Figs 6, 7 and 8 with respect to previous version

Scientific paper

Early-type galaxies (ETGs) are observed to be more compact at z>2 than in the local Universe. Remarkably, much of this size evolution appears to take place in a short (1.8 Gyr) time span between z=2.2 and z=1.3, which poses a serious challenge to hierarchical galaxy formation models where mergers occurring on a similar timescale are the main mechanism for galaxy growth. We compute the merger-driven redshift evolution of stellar mass Mstar\propto(1+z)^aM, half-mass radius Re\propto(1+z)^aR and velocity-dispersion sigma0\propto(1+z)^asigma predicted by concordance Lambda cold dark matter for a typical massive ETG in the redshift range z=1.3-2.2. Neglecting dissipative processes, and thus maximizing evolution in surface density, we find -1.52. Furthermore, we find that the scatter introduced in the size-mass correlation by the predicted merger-driven growth is difficult to reconcile with the tightness of the observed scaling law. We conclude that - barring unknown systematics or selection biases in the current measurements - minor and major mergers with spheroids are not sufficient to explain the observed size growth of ETGs within the standard model.

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