Obscuration in active galactic nuclei: near-infrared luminosity relations and dust colors

Abstract

We combine two approaches to isolate the AGN luminosity at near-IR wavelengths and relate the near-IR pure AGN luminosity to other tracers of the AGN. Using integral-field spectroscopic data of an archival sample of 51 local AGNs, we estimate the fraction of non-stellar light by comparing the nuclear equivalent width of the stellar 2.3 µm CO absorption feature with the intrinsic value for each galaxy. We compare this fraction to that derived from a spectral decomposition of the integrated light in the central arcsecond and find them to be consistent with each other. Using our estimates of the near-IR AGN light, we find a strong correlation with presumably isotropic AGN tracers. We show that a significant offset exists between type 1 and type 2 sources in the sense that type 1 sources are 7 (10) times brighter in the near-IR at log L MIR AGN = 42.5 (log L X AGN = 42.5). These offsets only become clear when treating infrared type 1 sources as type 1 AGNs. All AGNs have very red near-to mid-IR dust colors. This, as well as the range of observed near-IR temperatures, can be explained with a simple model with only two free parameters: the obscuration to the hot dust and the ratio between the warm and hot dust areas. We find obscurations of A hot V = 5 . . . 15 mag for infrared type 1 sources and A hot V = 15 . . . 35 mag for type 2 sources. The ratio of hot dust to warm dust areas of about 1000 is nicely consistent with the ratio of radii of the respective regions as found by infrared interferometry.

LLAMA: normal star formation efficiencies of molecular gas in the centres of luminous Seyfert galaxies

“…For the remaining three AGN, we adopted the AGN's K-band luminosity estimated from our multicomponent SED fits (Section 3.1). ESO 137-G034 and NGC 5728, two heavily obscured AGN, do not appear to show any AGN light in the K band to the limit of the Burtscher et al (2015) analysis, probably due to a high optical depth to NIR radiation in their AGN tori. Our estimates/limits on the AGN's NIR luminosities are plotted in Fig.…”

“…We therefore considered a lognormal distribution of M/L K specified by these values in our bootstrap analysis. The scatter of M/L K is the dominant source of uncertainty in these mass estimates, being greater than both the errors of the photometric measurements and the errors on nuclear luminosities from Burtscher et al (2015).…”

“…7 http://irsa.ipac.caltech.edu/Missions/2mass.html Burtscher et al (2015) are shown as red points (stars for measurements, small arrowheads for upper limits). The AGN luminosity measurements for NGC 6814, NGC 4388 and NGC 3081 lie outside the plotted range, and this is indicated by the large red arrows.…”

“…3 displays the integrated and beam-matched luminosities in the K s for all the LLAMA galaxies, indicating that the single-dish beams sample a few tens of per cent of the total NIR emission in these systems. Burtscher et al (2015) characterized the dilution of the stellar photospheric CO bandhead (2.3 µm) in a number of active galaxies, enabling a very sensitive measurement of the NIR luminosity of their AGN. This work has published constraints for 15 of the 18 LLAMA AGN and we adopted these measurements of the intrinsic K-band luminosity of their nuclear sources.…”

Compton-thick AGN in the 70-monthSwift-BAT All-Sky Hard X-ray Survey: A Bayesian approach

“…The fitting is performed in the 0.3-195 keV band using C statistic (Cash 1979) to avoid binning and therefore information loss. For very bright sources with more than 1000 counts, such as NGC1068 or Circinus, we exclude data below 2 keV to simplify the spectral modelling.…”