Evidence for a Geometrically Thick Self‐Gravitating Accretion Disk in NGC 3079

Abstract

We have mapped, for the first time, the full velocity extent of the water maser emission in NGC 3079. The largely north-south distribution of emission, aligned with a kiloparsec-scale molecular disk, and the segregation of blueshifted and redshifted emission on the sky are suggestive of a nearly edge-on molecular disk on parsec scales. Positions and line-of-sight velocities of blueshifted and redshifted maser emission are consistent with a central mass of $2 ; 10 6 M enclosed within a radius of $0.4 pc. The corresponding mean mass density of 10 6.8 M pc À3 is suggestive of a central black hole, which is consistent with the detection of hard X-ray excess (20-100 keV) and an Fe K line from the nucleus. Because the rotation curve traced by the maser emission is flat, the mass of the parsec-scale disk is significant with respect to the central mass. Since the velocity dispersion of the maser features does not decrease with radius and constitutes a large fraction of the orbital velocity, the disk is probably thick and flared. The rotation curve and the physical conditions necessary to support maser emission imply a Toomre Q-parameter that is T1. Thus, the disk is most likely clumpy, and we argue that it is probably forming stars. Overall, the accretion disk in NGC 3079 stands in contrast to the compact, thin, warped, differentially rotating disk in the archetypal maser galaxy NGC 4258.We have also mapped radio continuum emission in the vicinity of the disk and identify a new, time-variable, nonthermal component ( E) that is not collinear with the previously imaged putative jet. Based on the large luminosity and the unusually steep spectrum ( < À2:1), we exclude a radio supernova as the progenitor of E. However, because its spectrum is consistent with an aging electron energy distribution, E might be a rapidly cooling remnant, which may indicate that the jet axis wobbles. Alternatively, considering its location, the component might mark a shock in a wide-angle outflow that is interacting with a dense ambient medium. In this context, masers at high latitudes above the disk, mapped in this and previous studies, may be tracing an inward extension of the kiloparsec-scale bipolar wide-angle outflow previously observed along the galactic minor axis.

SUBMILLIMETER H2O MEGAMASERS IN NGC 4945 AND THE CIRCINUS GALAXY

“…Humphreys et al (2005) presented the first observations of H 2 O megamaser emission in a transition other than 22 GHz, detecting maser emission at 183 GHz and (tentatively) 439 GHz toward the galaxy NGC 3079. This galaxy had previously been known to host strong 22 GHz masers (Henkel et al 1984), with VLBI observations confirming that the 22 GHz emission originates from the galactic nucleus (Trotter et al 1998;Kondratko et al 2005). Although the signal-tonoise of the (sub)millimeter detections (∼7σ for the 183 GHz transition) was too low to permit detailed study, the maser emission appears to arise from several narrow (spectrally unresolved) features spanning a velocity range comparable to that of the 22 GHz emission.…”

A Deep 0.3–10 keV Spectrum of the H2O Maser Galaxy IC 2560

“…References.-(1) Greenhill et al 2007, in preparation; (2) ; (3) Molendi et al 2003;(18) Kondratko et al 2006b;(19) Guainazzi et al 2005;(20) Kondratko et al 2005; (21) Iyomoto et al 2001;(22) Braatz et al 1996;(23) Argon et al 2007, and references therein; (24) Fruscione et al 2005;(25) this paper. …”

“…f Guainazzi et al (2000). g Intrinsic luminosity quoted by (Kondratko et al 2006a), using PIMMS, does not take into account obscuration due to Compton scattering and may be significantly underestimated ).…”

How to Detect Inclined Water Maser Disks (and Possibly Measure Black Hole Masses)

“…The observational signatures of an inclined water maser disk, however, may also arise from other mechanisms. Water masers can be produced in radio jet-molecular cloud interactions (e.g., Gallimore et al 1996;Claussen et al 1998;Peck et al 2003;Henkel et al 2005), in star-forming regions (e.g., Tarchi et al 2002a,b;Henkel et al 2005;Hofner et al 2006;Darling et al 2008;Brogan et al 2010;Darling 2011;Tarchi et al 2011b;Amiri & Darling 2016), and in outflows (e.g., Greenhill et al 2003b;Kondratko et al 2005;Tarchi et al 2011a, but note that some objects in the latter survey may be candidates for inclined disk masers). These are likely to be the main contaminant among an inclined disk survey sample.…”