THE NUCLEAR INFRARED EMISSION OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI
ASTRONOMICAL JOURNAL 144:1 (2012) ARTN 11
Torus and active galactic nucleus properties of nearby Seyfert galaxies: Results from fitting infrared spectral energy distributions and spectroscopy
Astrophysical Journal 736:2 (2011)
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.The Small-Scale Mid-Infrared Emission of Low-Luminosity AGN
GALACTIC CENTER: A WINDOW TO THE NUCLEAR ENVIRONMENT OF DISK GALAXIES 439 (2011) 487-+
A high spatial resolution mid-infrared spectroscopic study of the nuclei and star-forming regions in luminous infrared galaxies
Astrophysical Journal 711:1 (2010) 328-349
Abstract:
We present a high spatial (diffraction-limited) resolution (∼0″.3) mid-infrared (MIR) spectroscopic study of the nuclei and star-forming regions of four local luminous infrared galaxies (LIRGs) using T-ReCS on the Gemini South telescope. We investigate the spatial variations of the features seen in the N-band spectra of LIRGs on scales of ∼100pc, which allow us to resolve their nuclear regions and separate the active galactic nucleus (AGN) emission from that of the star formation (SF). We compare (qualitatively and quantitatively) our Gemini T-ReCS nuclear and integrated spectra of LIRGs with those obtained with Spitzer IRS. Star-forming regions and AGNs show distinct features in the MIR spectra, and we spatially separate these, which is not possible using the Spitzer data. The 9.7 μm silicate absorption feature is weaker in the nuclei of the LIRGs than in the surrounding regions. This is probably due to the either clumpy or compact environment of the central AGN or young, nuclear starburst. We find that the [Ne II]12.81 μm luminosity surface density is tightly and directly correlated with that of Paα for the LIRG star-forming regions (slope of 1.00 ± 0.02). Although the 11.3 μmPAH feature shows also a trend with Paα, this is not common for all the regions and the slope is significantly lower. We also find that the [Ne II]12.81 μm/Paα ratio does not depend on the Paα equivalent width (EW), i.e., on the age of the ionizing stellar populations, suggesting that, on the scales probed here, the [Ne II]12.81 μm emission line is a good tracer of the SF activity in LIRGs. On the other hand, the 11.3 μmPAH/Paα ratio increases for smaller values of the Paα EW (increasing ages), indicating that the 11.3 μmPAH feature can also be excited by older stars than those responsible for the Paα emission. Finally, more data are needed in order to address the different physical processes (age of the stellar populations, hardness and intensity of the radiation field, mass of the star-forming regions) affecting the energetics of the polycyclic aromatic hydrocarbon features in a statistical way. Additional high spatial resolution observations are essential to investigating the SF in local LIRGs at the smallest scales and determining ultimately whether they share the same physical properties as high-z LIRGs, ULIRGs, and submillimiter galaxies and therefore belong to the same galaxy population. © 2010. The American Astronomical Society. All rights reserved.Erratum: Infrared spectroscopy and analysis of brown dwarf and planetary mass objects in the Orion nebula cluster
\mnras 399 (2009) 2288-2288-2288-2288