http://arxiv.org/abs/1810.05238
At redshifts below $z=2$, the majority of supermassive black hole (SMBH) mass estimates are obtained from modeling stellar kinematics or the dynamics of ionized molecular gas in the vicinity of the galaxy nucleus. For large early type galaxies, there appears to be a systematic disagreement between these two methods: stellar kinematics models predict higher masses than gas-dynamical models — an explicit example of which is M87, in which the discrepancy is a factor of two, more than 2 $\sigma$. Critical to the latter is the assumed underlying dynamical state of the gas; typically assumed to be on circular Keplerian orbits, potentially with some additional turbulent pressure support. This is inconsistent with models of the gas flow about low-accretion-rate SMBHs and at odds with observations of the Galactic Center. Thus, we present a simple model of non-Keplerian molecular disks and explore their implications for SMBH mass measurements. Specifically, we show that a larger central black hole with gas experiencing small amounts of radial motion can produce velocity curves similar to models that just contain circular Keplerian motions and a lower black hole mass. However, these non-Keplerian models are distinguishable from low-mass Keplerian models primarily through measurements of the velocity dispersion, wherein non-Keplerian models produce higher and narrower peak dispersions. Away from the galaxy center, but still within the circumnuclear gas disk, non-Keplerian models also become distinguishable from Keplerian models via a shift in the center of the velocity curve, related to the magnitude of the radial motion. The velocity model presented in this paper is capable of resolving the discrepancy between the ionized gas dynamics and stellar kinematics mass estimates, and is applicable to gas dynamical mass estimates of SMBHs in general.
B. Jeter, A. Broderick and B. McNamara
Mon, 15 Oct 18
24/56
Comments: 10 pages, 4 figures
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