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Register a new userNon-Keplerian rotation in the nucleus of NGC 1068: evidence for a massive accretion disk?
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The nucleus of the Seyfert galaxy NGC 1068 is believed to host a supermassive black hole. Evidence for the presence of a massive central object is provided by water maser emission, which displays a linear pattern in the sky, suggestive of a rotating disk. The rotating disk hypothesis is further strengthened by the declining shape of the derived rotation curve. Similar maser emission from NGC 4258 has led to a reliable estimate of the mass of the central black hole, because in this case the rotation curve is Keplerian. In the case of NGC 1068 the rotation curve traced by the water maser is non-Keplerian. In this paper we provide an interpretation of the non-Keplerian rotation in NGC 1068 by means of a self-gravitating accretion disk model. We obtain a good fit to the available data and derive a black hole mass M_{bh}=(8.0pm 0.3) 10^6M_{sun}. The resulting disk mass is comparable to the black hole mass. As an interesting by-product of our fitting procedure, we are able to estimate the viscosity parameter, which turns out to be alphaapprox 10^{-2}, in line with some theoretical expectations.
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The disks around some Herbig Be stars have been observed to be more compact than the expected dust sublimation radius for such objects, with highly refractory dust grains and optically thick gas emission having been proposed as possible explanations for this phenomenon. Our aim is to search for direct evidence for the presence of hot gas inside of the expected dust sublimation radius of MWC147. By combining VLTI/AMBER spectro-interferometry (R=12,000) with CRIRES spectroscopy (R=100,000) we can both spectrally and spatially resolve the Br-gamma line-emitting gas around MWC147. Our interferometric visibility modelling of MWC147 indicates the presence of a compact continuum disk with a close to face-on orientation. We model the continuum with an inclined Gaussian, as well as a ring with a radius of 0.60mas (0.39au) which is well within the expected dust sublimation radius of 1.52au. We detect no significant change in the measured visibilities across the Br-gamma line, indicating that the line-emitting gas is located in the same region as the continuum-emitting disk. We fit our AMBER spectro-interferometry data with a kinematic model of a disk in Keplerian rotation, with both the line-emitting and continuum-emitting components of the disk originating from the same compact region close to the central star. The presence of line-emitting gas in the same region as the K-band continuum supports the interpretation that the K-band continuum traces an optically-thick gas disk. Our spatially and spectrally resolved observations of MWC147 reveal that the K-band continuum and Br-gamma emission both originate from a similar compact region, with Br-gamma emitted from the accretion disk or disk wind region and exhibiting a rotational velocity profile. We conclude that we detect the presence of a compact, gaseous accretion disk in Keplerian rotation around MWC147.
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We present spectroscopic observations from the Hubble Space Telescope that reveal for the first time the presence of a broad pedestal of Balmer-line emission in the LINER galaxy NGC 4203. The emission-line profile is suggestive of a relativistic accretion disk, and is reminiscent of double-peaked transient Balmer emission observed in a handful of other LINERs. The very broad line emission thus constitutes clear qualitative evidence for a black hole, and spatially resolved narrow-line emission in NGC 4203 can be used to constrain its mass, with M_BH less than 6 x 10^6 solar masses at 99.7% confidence. This value implies a ratio of black-hole mass to bulge mass of less than approximately 7 x 10^-4 in NGC 4203, which is less by a factor of ~3 - 9 than the mean ratio obtained for other galaxies. The availability of an independent constraint on central black-hole mass makes NGC4203 an important testbed for probing the physics of weak active galactic nuclei. Assuming M_BH near the detection limit, the ratio of observed luminosity to the Eddington luminosity is approximately 10^-4. This value is consistent with advection-dominated accretion, and hence with scenarios in which an ion torus irradiates an outer accretion disk that produces the observed double-peaked line emission. Follow-up observations will make it possible to improve the black-hole mass estimate and study variability in the nuclear emission.
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Spectra of the archetypal Type II Seyfert galaxy NGC 1068 in a narrow wavelength interval near 3.7 microns have revealed a weak absorption feature due to two lines of the molecular ion H3+. The observed wavelength of the feature corresponds to velocity of -70 km/s relative to the systemic velocity of the galaxy, implying an outward flow from the nucleus along the line of sight. The absorption by H3+ along with the previously known broad hydrocarbon absorption at 3.4~microns probably are formed in diffuse gas that is in close proximity to the continuum source, i.e. within a few tens of parsecs of the central engine. Based on that conclusion and the measured H3+ absorption velocity and with the assumption of a spherically symmetric wind we estimate a rate of mass outflow from the AGN of ~1 Msun/yr.
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