We study the faint stellar halo of isolated central galaxies , by stacking galaxy images in the HSC survey and accounting for the residual sky background sampled with random points .
The surface brightness profiles in HSC r -band are measured for a wide range of galaxy stellar masses ( 9.2 < \log _ { 10 } M _ { \ast } / M _ { \odot } < 11.4 ) and out to 120 kpc .
Failing to account for the stellar halo below the noise level of individual images will lead to underestimates of the total luminosity by \leq 15 \% .
Splitting galaxies according to the concentration parameter of their light distributions , we find that the surface brightness profiles of low concentration galaxies drop faster between 20 and 100 kpc than those of high concentration galaxies .
Albeit the large galaxy-to-galaxy scatter , we find a strong self-similarity of the stellar halo profiles .
They show unified forms once the projected distance is scaled by the halo virial radius .
The colour of galaxies is redder in the centre and bluer outside , with high concentration galaxies having redder and more flattened colour profiles .
There are indications of a colour minimum , beyond which the colour of the outer stellar halo turns red again .
This colour minimum , however , is very sensitive to the completeness in masking satellite galaxies .
We also examine the effect of the extended PSF in the measurement of the stellar halo , which is particularly important for low mass or low concentration galaxies .
The PSF-corrected surface brightness profile can be measured down to \sim 31 \mathrm { mag } / \mathrm { arcsec } ^ { 2 } at 3- \sigma significance .
PSF also slightly flattens the measured colour profiles .