The Most Massive Galaxies with Large Depleted Cores: Structural Parameter Relations and Black Hole Masses

Abstract

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-Sérsic model to the galaxy spheroids. Using 28 “normal-core” (i.e., R b < 0.5 kpc) galaxies and one “large-core” (i.e., R b  > 0.5 kpc) galaxy from the literature, we constructed a final sample of 41 core-Sérsic galaxies. We find that large-core spheroids (with stellar masses M *  ≳ 10 12 M ☉ ) are not simple high-mass extensions of the less luminous normal-core spheroids having M *  ∼ 8 × 10 10 –10 12 M ☉ . While the two types follow the same strong relations between the spheroid luminosity L V and R b ( ), and the spheroid half-light radius R e ( , for ellipticals plus Brightest Cluster Galaxies), we discover a break in the core-Sérsic σ – 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 supermassive black hole (SMBH) masses M BH —3/11 galaxies are large-core galaxies—such that . However, for the large-core galaxies the SMBH masses estimated from the M BH – σ and core-Sérsic 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 harbor overmassive SMBHs ( M BH  ≳ 10 10 M ☉ ), considerably (∼3.7–15.6 σ and ∼0.6–1.7 σ ) larger than expectations from the spheroid σ and L , respectively. We suggest that the R b – M BH relation can be used to estimate SMBH masses in the most massive galaxies.