Haloes around edge-on disc galaxies in the Sloan Digital Sky Survey

ABSTRACT

We present a statistical analysis of halo emission for a sample of 1047 edge-on disc galaxies imaged in five bands by the Sloan Digital Sky Survey (SDSS). Stacking the homogeneously rescaled images of the galaxies, we can measure surface brightnesses as deep as  μ_r∼ 31 mag arcsec⁻² . The results strongly support the almost ubiquitous presence of stellar haloes around disc galaxies, whose spatial distribution is well described by a power law  ρ∝r⁻³ , in a moderately flattened spheroid  (c/a∼ 0.6) . The colour estimates in g–r and r–i, although uncertain, give a clear indication for extremely red stellar populations, hinting at old ages and/or non-negligible metal enrichment. These results support the idea of haloes being assembled via early merging of satellite galaxies.