We have reviewed the progress over the last century in modelling the distribution of stars in elliptical galaxies, plus the bulges of lenticular and spiral galaxies and their surrounding discs. A number of nearly forgotten or poorly recognised references have been identified. The universality, or at least versatility, of Sérsic's R1/n model to describe bulges (section 4.1) and elliptical galaxies (section 2.1) extends to the stellar halos of cD galaxies (section 2.4) and simulated dark matter halos (section 2.1.1).
Dwarf and ordinary elliptical galaxies were shown in section 3.1 to be united by two continuous linear relations between absolute magnitude and a) the stellar concentration quantified through Sérsic's (1963) R1/n shape parameter (section 3.1.2), and b) the central surface brightness, which is also related to the central density (section 3.1.1). As discussed in section 3.3, a break in the latter relation at MB -20.5 mag signals the onset of partially depleted cores relative to the outer Sérsic profile in luminous elliptical galaxies. Additional scaling relations are also noted to show a change in character at this magnitude, which may denote the onset of dry galaxy merging.
The identification of depleted galaxy cores and excess nuclear light relative to the outer Sérsic profile was discussed in sections 2.2, 2.2.1 and 2.3. After accounting for these features, it was revealed how the above two linear relations result in curved scaling relations involving effective half light radii and effective surface brightness (section 3.2). Specifically, the M - Re, M - µe, M - < µ >e, µe - Re, < µ >e - Re and n - Re relations are non-linear. These continuous curved relations exist because elliptical galaxies do not have a universal profile shape, such as an R1/4 profile, but instead a range of profile shapes that vary smoothly with absolute magnitude. Without an appreciation of the origin of these curved relations, they had in the past been heralded as evidence for a dichotomy between faint and bright elliptical galaxies. Numerical simulations and semi-numerical models which try to reproduce the full elliptical galaxy sequence must be able to reproduce these non-linear relations. This will likely require physical processes which work in tandem, albeit to different degrees over different mass ranges, to produce a continuum of galaxy properties that scale with mass while adhering to the linear M - n and M - µ0 relations (subject to core-formation).
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The upcoming 2.6 m VLT Survey Telescope (VST, Arnaboldi et al. 1998; Capaccioli et al. 2005), plus the 4×1.8 m Pan-STARRS array (Kaiser et al. 2002), the 4 m Visible and Infrared Survey Telescope for Astronomy (VISTA, Emerson et al. 2004) and the 8.4 m Large Synoptic Survey Telescope (LSST, Tyson 2002) are expected to deliver sub-arcsecond, deep and wide field-of-view imaging covering thousands of resolvable galaxies. By pushing down the luminosity function into the dwarf galaxy regime, and through the application of improved galaxy parameterisation methods which allow for structural non-homology and the 2- or 3-component nature of disc galaxies, both statistical and systematic errors will be reduced. This will undoubtedly provide improved constraints on galaxy scaling relations and, in turn, a fuller understanding of galaxy evolution.
This research was supported under the Australian Research Council's Discovery Projects funding scheme (DP110103509). This research has made use of NASA's Astrophysics Data System (ADS) Bibliographic Services and the NASA/IPAC Extragalactic Database (NED).