Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-02-17
Mon.Not.Roy.Astron.Soc.405:948-960,2010
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
15 pages, 10 Figures. Accepted by MNRAS
Scientific paper
10.1111/j.1365-2966.2010.16540.x
We discuss how the effective radius Phi(Re) function (ERF) recently worked out by Bernardi et al. (2009) represents a new testbed to improve the current understanding of Semi-analytic Models of Galaxy formation. In particular, we here show 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 (<10^11 \msun), and to a non-negligible fraction of compact (< 0.5-1 kpc) and massive galaxies (> 10^11 \msun). We also find that the latter discrepancy is smaller than previously claimed, and limited to only ultracompact (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 {\em and} size distributions allows a better understanding of where and how to improve models.
Bernardi Mariangela
Boylan-Kolchin Michael
Dai Xinyu
Khochfar Sadegh
Marulli Federico
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