The structural and photometric properties of early-type galaxies in hierarchical models

Abstract

We present predictions for the structural and photometric properties of early‐type galaxies in the Lambda cold dark matter (ΛCDM) cosmology from the published semi‐analytical galaxy formation models of Baugh et al. and Bower et al. These calculations were made with the galform code, which tracks the evolution of the disc and bulge components of a galaxy, using a self‐consistent model to compute the scalelengths. The sizes of galactic discs are determined by the conservation of the angular momentum of cooling gas. The sizes of merger remnants are computed by applying the virial theorem and conserving the binding energy of the progenitors and their orbital energy. There are a number of important differences between the two galaxy formation models. To suppress the overproduction of bright galaxies, the Bower et al. model employs active galactic nuclei heating to stifle gas cooling, whereas the Baugh et al. model invokes a superwind which ejects cooled gas. Also, in the Baugh et al. model a top‐heavy stellar initial mass function is adopted in starbursts. We compare the model predictions with observational results derived from the Sloan Digital Sky Survey. The model enjoys a number of notable successes, such as giving reasonable reproductions of the local Faber–Jackson relation (velocity dispersion–luminosity), the velocity dispersion–age relation, and the Fundamental Plane relating the luminosity, velocity dispersion and effective radius of spheroids. These achievements are all the more remarkable when one bears in mind that none of the parameters has been adjusted to refine the model predictions. We study how the residuals around the Fundamental Plane relation depend on galaxy properties. We examine in detail the physical ingredients of the calculation of galaxy sizes in galform, showing which components have the most influence over our results. We also study the evolution of the scaling relations with redshift. However, in spite of the successes, there are some important disagreements between the predictions of the model and observations: the brightest model spheroids have effective radii smaller than observed and the zero‐point of the Fundamental Plane shows little or no evolution with redshift in the model.

The Structure of Galaxies I: Surface Photometry Techniques

“…For example, structure of early-type galaxies is critical in distinguishing between cold dissipationless collapse versus hierarchical merging scenarios (Conselice 2008). These same models predict the ratio of spheroid to disk galaxies, as well as the distribution of bulge-to-disk ratios (Almeida, Baugh & Lacey 2007), so the structure of early-type galaxies is relevant to these predictions and their structural parameters are of importance to dark matter studies Both photometric and structural analysis are the domain of galaxy surface photometry (de Vaucouleurs 1948;Fish 1964;Freeman 1970). Surface photometry, the study of extended objects in the sky, has the primary goal of quantifying the 2D light distribution of galaxies (Milvang-Jensen & Jorgensen 1999) and ultimately reducing the isophotes to a 1D set of parameters.…”

Galaxy evolution by color-log(n) type since redshift unity in the Hubble Ultra Deep Field

“…Due to increases in computational power it has recently become possible to follow the evolution of disc and bulge sizes, as well as masses, in HC theory using semi-analytical techniques. Almeida et al (2007) adopt an approach in which spheroid sizes are computed following a merger by applying conservation of energy and the virial theorem. These authors are able to reproduce many features of the local elliptical galaxy population, such as the Fundamental Plane, and offer specific predictions for evolution of the elliptical luminosity-size relation with redshift, which are illustrated in their Fig.…”

On the Impact of Empirical and Theoretical Star Formation Laws on Galaxy Formation

“…The main successes of the Bow06 model are the reproduction of the observed break in the galaxy luminosity function (LF) at z = 0 in the b J and K bands, the observational inferred evolution of the stellar mass functions up to z ≈ 5, the bimodality in the colourmagnitude relation and the abundance and properties of red galaxies (Gonzalez-Perez et al 2009). The Bau05 model likewise matches b J -and K-band LFs at z = 0, but also the number counts and redshift distribution of submillimetre-selected galaxies (see also González et al 2011), disc sizes (Almeida, Baugh & Lacey 2007;González et al 2009), the evolution of Lyα emitters (Le Delliou et al 2006;Orsi et al 2008), counts, redshift distributions and LFs of galaxies selected in the mid-and far-IR and the Lyman-break galaxy LF at redshifts z = 3-10 .…”

“…The flatness of the predicted size-luminosity relations for spheroid-dominated galaxies in comparison with observations may result from the simplified calculation of the sizes of merger remnants, rather than implying that an additional mechanism is needed (see Almeida et al 2007;González et al 2009). This paper has been typeset from a T E X/L A T E X file prepared by the author.…”

“…Discussions of the differences between the models can be found in Almeida et al (2007), González et al (2009), Gonzalez-Perez et al (2009 and Lacey et al (2011). Briefly, the main differences between the models are the following.…”