Too big to be real? No depleted core in Holm 15a

Abstract

Partially depleted cores, as measured by core-Sérsic model "break radii," are typically tens to a few hundred parsecs in size. Here we investigate the unusually large (${R}_{\gamma \prime =0.5}$ = 4.57 kpc) depleted core recently reported for Holm 15A, the brightest cluster galaxy of Abell 85. We model the one-dimensional (1D) light profile, and also the two-dimensional (2D) image (using Galfit-Corsair, a tool for fitting the core-Sérsic model in 2D). We find good agreement between the 1D and 2D analyses, with minor discrepancies attributable to intrinsic ellipticity gradients. We show that a simple Sérsic profile (with a low index n and no depleted core) plus the known outer exponential "halo" provide a good description of the stellar distribution. We caution that while almost every galaxy light profile will have a radius where the negative logarithmic slope of the intensity profile $\gamma \prime$ equals 0.5, this alone does not imply the presence of a partially depleted core within this radius