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 45508 galaxies from SDSS DR9 in the redshift range 0.06 \leq z \leq 0.1 and in the mass range 10 ^ { 10.0 } M _ { \odot } < M _ { * } < 10 ^ { 11.4 } M _ { \odot } r. We derive surface brightness profiles to a depth of almost \mu _ { r } \sim 32 \mathrm { 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 ( C > 2.6 ) galaxies are more elliptical than those of low concentration ( C < 2.6 ) galaxies .
The g - r colour profile of high concentration galaxies reveals that the g - r colour of the stellar population in the stellar halo is bluer than in the main galaxy , and the colour of the stellar halo is redder for higher mass galaxies .
We further demonstrate that the full two-dimensional surface intensity distribution of our galaxy stacks can only be fit through multi-component Sérsic models .
Double-Sérsic profiles adequately model the average surface brightness distributions of high concentration galaxies , while triple-Sérsic profiles are often needed to model the surface brightness distributions of low concentration galaxies .
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 .
For high concentration galaxies , the fraction of accreted stellar light rises from 30 \% to 70 \% for galaxies in the stellar mass range from 10 ^ { 10.0 } M _ { \odot } to 10 ^ { 11.4 } M _ { \odot } .
The fraction of accreted light is much smaller in low concentration systems , increasing from 2 \% to 25 \% over the same mass range .
This work provides important constraints for the theoretical understanding of the formation of stellar haloes of galaxies .