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Register a new userThe Compton-Thick Seyfert 2 Nucleus of NGC3281: Torus Constraints from the 9.7$mu$m Silicate Absorption
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Dinalva Sales Aires
Publication date
2011
fields
Physics
and research's language is
English
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We present mid infrared (Mid-IR) spectra of the Compton-thick Seyfert 2 galaxy NGC,3281, obtained with the Thermal-Region Camera Spectrograph (T-ReCS) at the Gemini South telescope. The spectra present a very deep silicate absorption at 9.7,$mu$m, and [S{sc,iv]},10.5,$mu$m and [Ne{sc,ii]},12.7,$mu$m ionic lines, but no evidence of PAH emission. We find that the nuclear optical extinction is in the range 24 $leq$ A$_{V}$ $leq$ 83,mag. A temperature T = 300,K was found for the black-body dust continuum component of the unresolved 65,pc nucleus and at 130,pc SE, while the region at 130,pc reveals a colder temperature (200,K). We describe the nuclear spectrum of NGC,3281 using a clumpy torus model that suggests that the nucleus of this galaxy hosts a dusty toroidal structure. According to this model, the ratio between the inner and outer radius of the torus in NGC,3281 is $R_0/R_d$ = 20, with {bf 14} clouds in the equatorial radius with optical depth of $tau_{V}$ = 40,mag. We would be looking in the direction of the torus equatorial radius ($i$ = {bf 60$^{circ}$}), which has outer radius of R$_{0},sim$ 11,pc. The column density is N$_{H}approx$,{bf 1.2},$times,10^{24},cm^{-2}$ and iron K$alpha$ equivalent width ($approx$ 0.5 - 1.2,keV) are used to check the torus geometry. Our findings indicate that the X-ray absorbing column density, which classifies NGC,3281 as a Compton-thick source, may also be responsible for the absorption at 9.7,$mu$m providing strong evidence that the silicate dust responsible for this absorption can be located in the AGN torus.
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We present new NuSTAR and Chandra observations of NGC 3393, a galaxy reported to host the smallest separation dual AGN resolved in the X-rays. While past results suggested a 150 pc separation dual AGN, three times deeper Chandra imaging, combined with adaptive optics and radio imaging suggest a single, heavily obscured, radio-bright AGN. Using VLA and VLBA data, we find an AGN with a two-sided jet rather than a dual AGN and that the hard X-ray, UV, optical, NIR, and radio emission are all from a single point source with a radius <0.2. We find that the previously reported dual AGN is most likely a spurious detection resulting from the low number of X-ray counts (<160) at 6-7 keV and Gaussian smoothing of the data on scales much smaller than the PSF (0.25 vs. 0.80 FWHM). We show that statistical noise in a single Chandra PSF generates spurious dual peaks of the same separation (0.55$pm$0.07 vs. 0.6) and flux ratio (39$pm$9% vs. 32% of counts) as the purported dual AGN. With NuSTAR, we measure a Compton-thick source (NH=$2.2pm0.4times10^{24}$ cm$^{-2}$) with a large torus half-opening angle, {theta}=79 which we postulate results from feedback from strong radio jets. This AGN shows a 2-10 keV intrinsic to observed flux ratio of 150. Using simulations, we find that even the deepest Chandra observations would severely underestimate the intrinsic luminosity of NGC 3393 above z>0.2, but would detect an unobscured AGN of this luminosity out to high redshift (z=5).
Mid-infrared (MIR) spectra observed with Gemini/Michelle were used to study the nuclear region of the Compton-thick Seyfert 2 (Sy 2) galaxy Mrk 3 at a spatial resolution of $sim$200 pc. No polycyclic aromatic hydrocarbons (PAHs) emission bands were detected in the N-band spectrum of Mrk 3. However, intense [Ar III] 8.99 $mu$m, [S IV] 10.5 $mu$m and [Ne II] 12.8 $mu$m ionic emission-lines, as well as silicate absorption feature at 9.7$mu$m have been found in the nuclear extraction ($sim$200 pc). We also present subarcsecond-resolution Michelle N-band image of Mrk 3 which resolves its circumnuclear region. This diffuse MIR emission shows up as a wings towards East-West direction closely aligned with the S-shaped of the Narrow Line Region (NLR) observed at optical [O III]$lambda$5007AA image with Hubble/FOC. The nuclear continuum spectrum can be well represented by a theoretical torus spectral energy distribution (SED), suggesting that the nucleus of Mrk 3 may host a dusty toroidal structure predicted by the unified model of active galactic nucleus (AGN). In addition, the hydrogen column density (N$_H,=,4.8^{+3.3}_{-3.1}times,10^{23}$ cm$^{-2}$) estimated with a torus model for Mrk 3 is consistent with the value derived from X-ray spectroscopy. The torus model geometry of Mrk 3 is similar to that of NGC 3281, both Compton-thick galaxies, confirmed through fitting the 9.7$mu$m silicate band profile. This results might provide further evidence that the silicate-rich dust can be associated with the AGN torus and may also be responsible for the absorption observed at X-ray wavelengths in those galaxies.
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