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

TL;DR

This study re-examines the large depleted core reported in Holm 15A, demonstrating that a simple Sersic profile without a depleted core can adequately describe its stellar distribution, challenging previous claims.

Contribution

The paper shows that Holm 15A's large core is not real and can be explained by a Sersic profile, providing a new perspective on galaxy core measurements.

Findings

Holm 15A's core can be modeled without a depleted core.

A simple Sersic profile plus an outer halo fits the data well.

The large core previously reported is likely an artifact, not a physical depletion.

Abstract

Partially depleted cores, as measured by core-Sersic model "break radii", are typically tens to a few hundred parsecs in size. Here we investigate the unusually large (cusp radius of 4.57 kpc) depleted core recently reported for Holm 15A, the brightest cluster galaxy of Abell 85. We model the 1D light profile, and also the 2D image (using GALFIT-CORSAIR, a tool for fitting the core-Sersic 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 Sersic 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 equals 0.5, this alone does not imply the presence of a partially depleted core within this radius.