Dynamical measurements of black hole masses in four brightest cluster galaxies at 100 Mpc

Abstract

We present stellar kinematics and orbit superposition models for the central regions of four brightest cluster galaxies, based upon integral-field spectroscopy at Gemini, Keck, and McDonald Observatories. Our integral-field data span radii from <100 pc to tens of kiloparsecs, comparable to the effective radius of each galaxy. We report black hole masses, M •, of 2.1+1.6-1.6 × 1010 M for NGC4889, 9.7+3.0-2.5 × 109 M for NGC3842, and 1.3+0.5-0.4 × 109 M ⊙ for NGC7768, with errors representing 68% confidence limits. For NGC2832, we report an upper limit of M • < 9.0 × 109 M ⊙. Our models of each galaxy include a dark matter halo, and we have tested the dependence of M • on the model dark matter profile. Stellar orbits near the center of each galaxy are tangentially biased, on comparable spatial scales to the galaxies' photometric cores. We find possible photometric and kinematic evidence for an eccentric torus of stars in NGC4889, with a radius of nearly 1kpc. We compare our measurements of M • to the predicted black hole masses from various fits to the relations between M • and stellar velocity dispersion (σ), luminosity (L), or stellar mass (M ⊙). Still, the black holes in NGC4889 and NGC3842 are significantly more massive than all σ-based predictions and most L-based predictions. The black hole in NGC7768 is consistent with a broader range of predictions. © 2012. The American Astronomical Society. All rights reserved.