Testing the predictions of the cold dark matter model for the sizes, colours, morphologies and luminosities of galaxies with the SDSS

TL;DR

This study tests predictions of cold dark matter galaxy formation models against SDSS data, focusing on galaxy sizes, colours, morphologies, and luminosities, revealing strengths and shortcomings of current models.

Contribution

It compares two semi-analytical galaxy formation models within the CDM framework to SDSS observations, highlighting their successes and limitations in reproducing galaxy properties.

Findings

Bower et al. model better matches luminosity function and colour bimodality.

Baugh et al. model predicts size-luminosity relation for late-type galaxies.

Both models struggle to reproduce sizes of bright early-type galaxies.

Abstract

The huge size and uniformity of the Sloan Digital Sky Survey makes possible an exacting test of current models of galaxy formation. We compare the predictions of the GALFORM semi-analytical galaxy formation model for the luminosities, morphologies, colours and scale-lengths of local galaxies. GALFORM models the luminosity and size of the disk and bulge components of a galaxy, and so we can compute quantities which can be compared directly with SDSS observations, such as the Petrosian magnitude and the Sersic index. We test the predictions of two published models set in the cold dark matter cosmology: the Baugh et al. (2005) model, which assumes a top-heavy initial mass function (IMF) in starbursts and superwind feedback, and the Bower et al. (2006) model, which uses AGN feedback and a standard IMF. The Bower et al model better reproduces the overall shape of the luminosity function, the morphology-luminosity relation and the colour bimodality observed in the SDSS data, but gives a poor match to the size-luminosity relation. The \Baugh et al. model successfully predicts the size-luminosity relation for late-type galaxies. Both models fail to reproduce the sizes of bright early-type galaxies. These problems highlight the need to understand better both the role of feedback processes in determining galaxy sizes, in particular the treatment of the angular momentum of gas reheated by supernovae, and the sizes of the stellar spheroids formed by galaxy mergers and disk instabilities.