The most massive galaxies with large depleted cores: structural parameter relations and black hole masses

TL;DR

This study investigates the structural properties and black hole masses of the most massive galaxies with large depleted cores, revealing that these galaxies host overmassive black holes and differ from less luminous core galaxies.

Contribution

It provides the first detailed analysis of large-core galaxies with R_b > 0.5 kpc, establishing new relations between core size, galaxy luminosity, and black hole mass.

Findings

Large-core galaxies are not simple extensions of less luminous core galaxies.

A break in the sigma-L_V relation occurs at M_V ~ -23.50 mag.

Large-core galaxies host overmassive SMBHs compared to expectations.

Abstract

[Abridged] Luminous spheroids (M_V < - 21.50 +- 0.75 mag) contain partially depleted cores with sizes (R_ b) typically 0.02 - 0.5 kpc. However, galaxies with R_b > 0.5 kpc are rare and poorly understood. Here we perform detailed decompositions of the composite surface brightness profiles, extracted from archival Hubble Space Telescope and ground-based images, of 12 extremely luminous "large-core" galaxies that have R_b > 0.5 kpc and M_V < -23.50 +- 0.10 mag, fitting a core-S\'ersic model to the galaxy spheroids. Using 28 "normal-core" (i.e., R_b < 0.5 kpc) galaxies and 1 "large-core" (i.e., R_b > 0.5 kpc) galaxy from the literature, we constructed a final sample of 41 core-S\'ersic galaxies. We find that large-core spheroids (with stellar masses M_* > 10^12 M_sun) are not simple high-mass extensions of the less luminous normal-core spheroids having M_* ~ 8 x 10^10 - 10^12 M_sun. While the two types follow the same strong relations between the spheroid luminosity L_V and R_b (R_b prop L_V^(1.38 +- 0.13), and the spheroid half-light radius R_e (R_e prop L_V^(1.08 +- 0.09), for ellipticals plus BCGs), we discover a break in the core-S\'ersic sigma-L_V relation occurring at M_V ~ -23.50 +- 0.10 mag. Furthermore, we find a strong log-linear R_b-M_BH relation for the 11 galaxies in the sample with directly determined SMBH masses M_BH---3/11 galaxies are large-core galaxies ---such that R_b prop M_BH^(0.83 +- 0.10). However, for the large-core galaxies the SMBH masses estimated from the M_BH-sigma and core-S\'ersic M_BH-L relations are undermassive, by up to a factor of 40, relative to expectations from their large R_b values, confirming earlier results. Our findings suggest that large-core galaxies harbour overmassive SMBHs (M_BH > 10^10 M_sun), considerably (~ 3.7-15.6 sigma and ~ 0.6-1.7 sigma) larger than expectations from the spheroid sigma and L, respectively.