Journal Article

Size and velocity-dispersion evolution of early-type galaxies in a <i>Λ</i> cold dark matter universe

Carlo Nipoti, Tommaso Treu, Alexie Leauthaud, Kevin Bundy, Andrew B. Newman and Matthew W. Auger

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 422, issue 2, pages 1714-1731
Published in print May 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20749.x
Size and velocity-dispersion evolution of early-type galaxies in a Λ cold dark matter universe

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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 1.3, which poses a serious challenge to hierarchical galaxy formation models where mergers occurring on a similar time-scale are the main mechanism for galaxy growth. We compute the merger-driven redshift evolution of stellar mass , half-mass radius and velocity dispersion predicted by concordance Λ 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 −1.5 ≲aM≲−0.6, −1.9 ≲aR≲−0.7 and 0.06 ≲aσ≲ 0.22, under the assumption that the accreted satellites are spheroids. It follows that the predicted z∼ 2.2 progenitors of z∼ 1.3 ETGs are significantly less compact (on average a factor of ∼2 larger Re at given M*) than the quiescent galaxies observed at z≳ 2. 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.

Keywords: galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: formation; galaxies: kinematics and dynamics; galaxies: structure

Journal Article.  13299 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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