A Non-Parametric Estimate of Mass 'Scoured' in Galaxy Cores

TL;DR

This paper introduces a non-parametric method to estimate the stellar mass deficits in galaxy cores, revealing how these deficits scale with radius and black hole mass, and confirming models of black hole binary scouring.

Contribution

It provides a direct, model-independent measurement of mass deficits in galaxy cores using stellar mass profiles, avoiding assumptions about profile shapes.

Findings

Mass deficit increases as a power-law with radius, up to ~2-4 times the black hole mass.

No significant difference in mass deficits between different stellar mass galaxies beyond 100pc.

Results align with theoretical models of black hole binary scouring effects.

Abstract

We present a simple estimate of the mass 'deficits' in cored spheroids, as a function of galaxy mass and radius within the galaxy. Previous attempts to measure such deficits depended on fitting some functional form to the profile at large radii and extrapolating inwards; this is sensitive to the assumed functional form and does not allow for variation in nuclear profile shapes. We take advantage of larger data sets to directly construct stellar mass profiles of observed systems and measure the stellar mass enclosed in a series of physical radii (M(<R)), for samples of cusp and core spheroids at the same stellar mass. There is a significant bimodality in this distribution at small radii, and we non-parametrically measure the median offset between core and cusp populations (the deficit Delta_M(<R)). We construct the scoured mass profile as a function of radius, without reference to any assumed functional form. The mass deficit rises in power-law fashion (Delta_M(<R) R^{1.3-1.8}) from a significant but small mass at R<10pc, to asymptote to a maximum ~0.5-2 M_BH at ~100pc. At larger radii there is no statistically significant separation between populations; the upper limit to the cumulative scoured mass at ~kpc is ~2-4 M_BH. This does not depend strongly on stellar mass. The dispersion in M(<R) appears larger in the core population, possibly reflecting the fact that scouring increases the scatter in profile shapes. These results are in good agreement with models of scouring from BH binary systems.