Work

Resolving the mid-infrared cores of local Seyferts

Year: 2009

Type: article

Abstract: We present new photometry of 16 local Seyferts including 6 Compton-thick sources in N-band filters around 12-μm, obtained with the VISIR instrument on the 8-m Very Large Telescope. The near-diffraction-limited imaging provides the least-contaminated core fluxes for these sources to date. Augmenting these with our previous observations and with published intrinsic X-ray fluxes, we form a total sample of 42 sources for which we find a strong mid-infrared:X-ray (12.3 μm:2–10 keV) luminosity correlation. Performing a physically-motivated subselection of sources in which the Seyfert torus is likely to be best-resolved results in the correlation LMIR LX, with a reduction of the scatter in luminosities as compared to the full sample. Consideration of systematics suggests a range of 1.02–1.21 for the correlation slope. The mean 2-keV:12.3-μm spectral index () is found to be -1.100.01, largely independent of luminosity. Indirectly-computed 12-μm bolometric corrections range over ≈10–30 if a known luminosity trend of X-ray bolometric corrections is assumed. Comparison with ISO data spanning a wider luminosity range suggests that our correlation can be extended into the quasar regime. That unobscured, obscured, and Compton-thick sources all closely follow the same luminosity correlation has important implications for the structures of Seyfert cores. The typical resolution-limit of our imaging corresponds to ~70 pc at a median , and we use the tightness of the correlation to place constraints on the dominance of any residual emission sources within these physical scales. An upper-limit for any contaminating star formation of ≈40% of the unresolved flux is inferred, on average. We suggest that uncontaminated mid-IR continuum imaging of AGN is an accurate proxy for their intrinsic power.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/200811368

Authors: P. Gandhi, H. Horst, A. Smette, S. Hönig, A. Comastri, R. Gilli, C. Vignali, W. Duschl