Parametrizing the stellar haloes of galaxies

We study the stellar haloes of galaxies out to 70-100 kpc as a function of stellar mass and galaxy type by stacking aligned r- and g-band images from a sample of 45 508 galaxies from Sloan Digital Sky Survey Data Release 9 in the redshift range 0.06 <= z <= 0.1 and in the mass range 10(10.0) M-circle dot < M-* < 10(11.4) M-circle dot. We derive surface brightness profiles to a depth of almost mu(r) similar to 32 mag arcsec(-2). We find that the ellipticity of the stellar halo is a function of galaxy stellar mass and that the haloes of high-concentration galaxies are more elliptical than those of low-concentration galaxies. Where the g - r colour of the stellar halo can be measured, we find that the stellar light is always bluer than in the main galaxy. The colour of the stellar halo is redder for more massive galaxies. We further demonstrate that the full two-dimensional surface intensity distribution of our galaxy stacks can only be fit through multicomponent Sersic models. Using the fraction of light in the outer component of the models as a proxy for the fraction of accreted stellar light, we show that this fraction is a function of stellar mass and galaxy type. The fraction of accreted stellar light rises from 30 to 70 per cent and from 2 to 25 per cent for high-and low-concentration galaxies, respectively, over the mass range 10(10.0)-10(11.4) M-circle dot.