Prof Patrick Roche

Abstract:

Fine-structure mid-infrared emission lines with critical densities in the regime 104 ≤ ncrit ≤ 106cm-3 can be employed to probe the outflow from Wolf-Rayet (WR) stars at radii of ~1015cm. Narrow-band mid-infrared imaging and spectroscopy of the nearest WR star to the Sun, γVelorum is analysed for spatially resolved forbidden line emission in the WR outer wind. The [Siv] 10.52-μm and [Neii] 12.81-μm emission regions are found to be spatially extended, compared to unresolved continuum and He and C recombination line emission. The [Siv] and [Neii] emission line distributions have a high degree of azimuthal symmetry, indicating a spherically symmetric outflow. A model wind with a modest degree of clumping (clumping factor f ~ 10) provides a better match to the observations than an unclumped model. The overall line intensity distributions are consistent with a freely expanding, spherically symmetric 1/r2 outflow with constant ionization fraction and modestly clumped density structure. © 2012 The Authors Monthly Notices of the Royal Astronomical Society. © 2012 RAS.

Abstract:

We have obtained high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs) and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGN; Lbol < 5 × 1042 erg s-1). Infrared (IR) observations may advance our understanding of the accretion ows in LLAGN, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGN have not yet been well-determined. In these proceedings we summarise the results for the LLAGN at the relatively high-luminosity, high-Eddington ratio end of the sample. Strong, compact nuclear sources are visible in the MIR images of these objects, with luminosities consistent with or slightly in execss of that predicted by the standard MIR/X-ray relation. Their broadband nuclear SEDs are diverse; some resemble typical Seyfert nuclei, while others possess less of a well-defined MIR "dust bump". Strong silicate emission is present in many of these objects. We speculate that this, together with high ratios of silicate strength to hydrogen column density, could suggest optically thin dust and low dust-to-gas ratios, in accordance with model predictions that LLAGN do not host a Seyfert-like obscuring torus.

Abstract:

We used the CLUMPY torus models and a Bayesian approach to fit the infrared spectral energy distributions and ground-based high angular resolution mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This allowed us to put tight constraints on torus model parameters such as the viewing angle i, the radial thickness of the torus Y, the angular size of the cloud distribution σtorus, and the average number of clouds along radial equatorial rays N0. We found that the viewing angle i is not the only parameter controlling the classification of a galaxy into type 1 or type2. In principle, type 2s could be viewed at any viewing angle i as long as there is one cloud along the line of sight. A more relevant quantity for clumpy media is the probability for an active galactic nucleus (AGN) photon to escape unabsorbed. In our sample, type 1s have relatively high escape probabilities, Pesc ∼ 12%-44%, while type 2s, as expected, tend to have very low escape probabilities. Our fits also confirmed that the tori of Seyfert galaxies are compact with torus model radii in the range 1-6pc. The scaling of the models to the data also provided the AGN bolometric luminosities L bol(AGN), which were found to be in good agreement with estimates from the literature. When we combined our sample of Seyfert galaxies with a sample of PG quasars from the literature to span a range of Lbol(AGN) ∼ 1043-1047 erg s-1, we found plausible evidence of the receding torus. That is, there is a tendency for the torus geometrical covering factor to be lower (f2 ∼ 0.1-0.3) at high AGN luminosities than at low AGN luminosities (f2 ∼ 0.9-1 at ∼ 1043-1044 erg s-1). This is because at low AGN luminosities the tori appear to have wider angular sizes (larger σtorus) and more clouds along radial equatorial rays. We cannot, however, rule out the possibility that this is due to contamination by extended dust structures not associated with the dusty torus at low AGN luminosities, since most of these in our sample are hosted in highly inclined galaxies. © 2011. The American Astronomical Society. All rights reserved.