Deep Surface Brightness Profiles of Spiral Galaxies from SDSS Stripe82:   Touching Stellar Halos
  Using SDSS Stripe82 data we have obtained deep radial surface brightness profiles of 7 face-on to intermediate inclined late-type spirals down to \sim 30 mag arcsec^-2 in the r'-band. We do not find any evidence for a sharp cut-off of the light distribution of the disks but a smooth continuation into the stellar halos of galaxies. Stellar halos start to affect the surface brightness profiles of the galaxies at \sim 28 mag arcsec^-2, and at a radial distance of \sim 4-10 inner scale-lengths. We find that the light contribution from the stellar halo could be responsible of previous classification of surface brightness profiles as Type III in late-type galaxies. In order to estimate the contribution of the stellar halo light to the total galaxy light, we carried out a Bulge/Disk/Stellar Halo decomposition by simoultaneously fitting all components. The light contribution of the halo to the total galaxy light varies from ~ 1% to ~ 5%, but in case of ongoing mergers, the halo light fraction can be as high as ~ 10%, independently of the luminosities of the galaxies. We have also explored the integrated (g'-r') color of the stellar halo of our galaxies. We find (g'-r') colors ranging from ~ 0.4 to ~ 1.2. By confronting these colors with model predictions, we encounter problems to fit our very red colors onto stellar population grids with conventional IMFs. Very red halo colors can be attributed to stellar populations dominated by very low mass stars of low to intermediate metallicity produced by bottom-heavy IMFs. 
Judit Bakos and Ignacio Trujillo
astro-ph.CO