Vertically Self-Gravitating ADAFs in the Presence of Toroidal Magnetic Field

Force due to the self-gravity of the disc in the vertical direction is considered to study its possible effects on the structure of a magnetized advection-dominated accretion disc. We present steady-sate self similar solutions for the dynamical structure of such a type of the accretion flows. Our solutions imply reduced thickness of the disc because of the self-gravity. It also imply that the thickness of the disc will increase by adding the magnetic field strength.Comment: Accepted for publication in Astrophysics and Space Science

The mid IR - hard X-ray correlation in AGN and its implications for dusty torus models.

Context: We investigate mid-infrared and X-ray properties of the dusty torus invoked in the unification scenario for active galactic nuclei. Aims: We use the relation between mid IR and hard X-ray luminosities to constrain the geometry and physical state of the dusty torus. Methods: We present new VISIR observations of 17 nearby AGN and combine these with our earlier VISIR sample of 8 Seyfert galaxies. Combining these observations with X-ray data from the literature we study the correlation between their mid IR and hard X-ray luminosities. Results: A statistically highly significant correlation between the rest frame 12.3 mircon (L_MIR) and 2-10 keV (L_X) luminosities is found. Furthermore, with a probability of 97%, we find that Sy 1 and Sy 2 have the same distribution of L_MIR over L_X. Conclusions: The high resolution of our MIR imaging allows us to exclude any significant non-torus contribution to the AGN mid IR continuum,thereby implying that the similarity in the L_MIR / L_X ratio between Sy 1s and Sy 2s is intrinsic to AGN. We argue that this is best explained by clumpy torus models. The slope of the correlation is in good agreement with the expectations from the unified scenario and indicates little to no change of the torus geometry with luminosity. In addition, we demonstrate that the high angular resolution is crucial for AGN studies in the IR regime.Comment: accepted for publication in Astronomy & Astrophysics, 13 pages, 4 figure

Mid-infrared properties of nearby low-luminosity AGN at high angular resolution.

High spatial resolution mid-infrared (MIR) 12 \mum continuum imaging of low-luminosity active galactic nuclei (LLAGN) obtained by VLT/VISIR is presented. The goal of this investigation is to determine if the nuclear MIR emission of LLAGN is consistent with the existence of a dusty obscuring torus. A sample of 17 nearby LLAGN was selected and combined with archival VISIR data of 9 additional LLAGN with available X-ray measurements. Of the 17 observed LLAGN, 7 are detected, while upper limits are derived for the 10 non-detections. All detections except NGC 3125 appear point-like on a spatial scale of \sim 0.35". The detections do not significantly deviate from the known MIR-X-ray correlation but extend it by a factor of \sim 10 down to luminosities < 10^41 erg/s with a narrow scatter. The latter is dominated by the uncertainties in the X-ray luminosity. Interestingly, a similar correlation with comparable slope but with a normalization differing by \sim 2.6 orders of magnitude has been found for local starburst galaxies. In addition, the VISIR data are compared with lower spatial resolution data from Spitzer/IRS and IRAS. By using a scaled starburst template SED and the PAH 11.3 \mum emission line the maximum nuclear star formation contamination to the VISIR photometry is restricted to < 30% for 75% of the LLAGN. Exceptions are NGC 1097 and NGC 1566, which may possess unresolved strong PAH emission. Furthermore, within the uncertainties the MIR-X-ray luminosity ratio is unchanged over more than 4 orders of magnitude in accretion rate. These results are consistent with the existence of the dusty torus in all observed LLAGN, although the jet or accretion disk as origin of the MIR emission cannot be excluded. Finally, the fact that the MIR-X-ray correlation holds for all LLAGN and Seyferts makes it a very useful empirical tool for converting between the MIR and X-ray powers of these nuclei.Comment: 19 pages, 7 figures, accepted for publication in A&

Resolved Mid-Infrared Imaging of AGN: An Isotropic Measure of Intrinsic Power

We present a strong correlation between 12&#956;m mid-IR and intrinsic X-ray (2\u201310 keV) luminosities of local Seyferts. This work is based on new diffraction-limited mid-IR observations with the 8-m Very Large Telescope (VLT), resulting in the least-contaminated core fluxes of 42 Seyferts to date

Resolved mid-infrared imaging of AGN: an isotropic measure of intrinsic power

We present new results suggesting that resolved mid-infrared (mid-IR) imaging of active galactic nuclei (AGN) is an isotropic probe of their intrinsic luminosities