Journal Article

Further constraining galaxy evolution models through the size function of SDSS early-type galaxies

Francesco Shankar, Federico Marulli, Mariangela Bernardi, Michael Boylan-Kolchin, Xinyu Dai and Sadegh Khochfar

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 405, issue 2, pages 948-960
Published in print June 2010 | ISSN: 0035-8711
Published online June 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16540.x
Further constraining galaxy evolution models through the size function of SDSS early-type galaxies

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We discuss how the effective radius Re function (ERF) recently worked out by Bernardi et al. represents a new testbed to improve the current understanding of semi-analytic models of galaxy formation. In particular, we show here that a detailed hierarchical model of structure formation can broadly reproduce the correct peak in the size distribution of local early-type galaxies, although it significantly overpredicts the number of very compact and very large galaxies. This in turn is reflected in the predicted size–mass relation, much flatter than the observed one, due to too large (≳3 kpc) low-mass galaxies (<1011 M), and to a non-negligible fraction of compact (≲0.5–1 kpc) and massive galaxies (≳1011 M). We also find that the latter discrepancy is smaller than previously claimed, and limited to only ultra-compact (Re ≲ 0.5 kpc) galaxies when considering elliptical-dominated samples. We explore several causes behind these effects. We conclude that the former problem might be linked to the initial conditions, given that large and low-mass galaxies are present at all epochs in the model. The survival of compact and massive galaxies might instead be linked to their very old ages and peculiar merger histories. Overall, knowledge of the galactic stellar mass and size distributions allows a better understanding of where and how to improve models.

Keywords: galaxies: evolution; galaxies: formation; galaxies: structure; cosmology: theory

Journal Article.  9984 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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