http://arxiv.org/abs/1310.3823
We show that the wealth of recent work on trends in galaxy sizes with mass and redshift can be understood in terms of the influence of underlying cosmic evolution; a holistic view which is complimentary to the usual interpretations involving the accumulation of discreet evolutionary processes acting on individual objects. Using analytic predictions from standard cosmology theory, supported with the results of the Millennium simulations, we begin by deriving the size trends in the population of collapsed cosmic structures, and emphasise the important distinction between these trends and the hierarchical assembly of individual structures. Moving on to galaxies, we argue that the observed variation in galactic stellar mass, as a function of inferred host structure mass, can be understood to first order in terms of natural limitations of cooling and feedback. But whilst this fractional stellar mass content varies by orders of magnitude, the characteristic radius of galaxies has been found to correlate strongly and linearly with that of the host structure. Using analytic arguments, illustrated with mock populations generated from the Millennium simulations, we then explain how these two aspects will lead to galaxy sizes that closely follow recently observed trends and their evolution, and verify this with direct comparison to galaxies from the COSMOS and SDSS surveys. Thus we conclude that it may be possible to understand the observed minimum radius for galaxies, the evolving trend in size as a function of mass for intermediate systems, and the observed increase in the sizes of massive galaxies, as being an emergent consequence of the cosmic expansion.
Date added: Wed, 16 Oct 13