The supermassive black hole in M84 revisited

J.L. Walsh, A. Barth, M. Sarzi

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    The mass of the central black hole in the giant elliptical galaxy M84 has previously been measured by two groups using the same observations of emission-line gas with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope, giving strongly discrepant results: Bower et al. found M BH = (1.5+1.1 –0.6) × 109 M , while Maciejewski & Binney estimated M BH = 4 × 108 M . In order to resolve this discrepancy, we have performed new measurements of the gas kinematics in M84 from the same archival data and carried out comprehensive gas-dynamical modeling for the emission-line disk within ~70 pc from the nucleus. In comparison with the two previous studies of M84, our analysis includes a more complete treatment of the propagation of emission-line profiles through the telescope and STIS optics, as well as inclusion of the effects of an intrinsic velocity dispersion in the emission-line disk. We find that an intrinsic velocity dispersion is needed in order to match the observed line widths, and we calculate gas-dynamical models both with and without a correction for asymmetric drift. Including the effect of asymmetric drift improves the model fit to the observed velocity field. Our best-fitting model with asymmetric drift gives M BH = (8.5+0.9 –0.8) × 108 M (68% confidence). This is a factor of ~2 smaller than the mass often adopted in studies of the M BH-σ and M BH-L relationships. Our result provides a firmer basis for the inclusion of M84 in the correlations between black hole mass and host galaxy properties. [see original online version for correct notation]
    Original languageEnglish
    Pages (from-to)762-776
    JournalThe Astrophysical Journal
    Issue number1
    Publication statusPublished - 2010


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