Astrophys. J., 716, 1151-1165 (2010/June-3)
Mid-infrared properties of the Swift burst alert telescope active galactic nuclei sample of the local universe. I. Emission-line diagnostics.
WEAVER K.A., MELENDEZ M., MUSHOTZKY R.F., KRAEMER S., ENGLE K., MALUMUTH E., TUELLER J., MARKWARDT C., BERGHEA C.T., DUDIK R.P., WINTER L.M. and ARMUS L.
Abstract (from CDS):
We compare mid-infrared emission-line properties from high-resolution Spitzer spectra of a hard X-ray (14-195 keV) selected sample of nearby (z < 0.05) active galactic nuclei (AGNs) detected by the Burst Alert Telescope (BAT) aboard Swift. The luminosity distribution for the mid-infrared emission lines, [O IV] 25.89 µm, [Ne II] 12.81 µm, [Ne III] 15.56 µm, and [Ne V] 14.32/24.32 µm, and hard X-ray continuum show no differences between Seyfert 1 and Seyfert 2 populations; however, six newly discovered BAT AGNs are under-luminous in [O IV], most likely the result of dust extinction in the host galaxy. The overall tightness of the mid-infrared correlations and BAT fluxes and luminosities suggests that the emission lines primarily arise in gas ionized by the AGNs. We also compare the mid-infrared emission lines in the BAT AGNs with those from published studies of ULIRGs, Palomar-Green quasars, star-forming galaxies, and LINERs. We find that the BAT AGN sample falls into a distinctive region when comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] ratios. These line ratios are lower in sources that have been previously classified in the mid-infrared/optical as AGNs than those found for the BAT AGNs, suggesting that, in our X-ray selected sample, the AGNs represent the main contribution to the observed line emission. These ratios represent a new emission line diagnostic for distinguishing between AGNs and star-forming galaxies.
galaxies: active - galaxies: Seyfert - infrared: galaxies - X-rays: galaxies
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