THE COMPTON-THICK SEYFERT 2 NUCLEUS OF NGC 3281: TORUS CONSTRAINTS FROM THE 9.7 {mu}m SILICATE ABSORPTION
- Departamento de Astronomia, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, Porto Alegre, RS (Brazil)
- Gemini Observatory, c/o Aura, Inc., Casilla 603, La Serena (Chile)
- Laboratorio Nacional de Astrofisica/MCT, Rua dos Estados Unidos 154, Itajuba, MG (Brazil)
We present mid-infrared (mid-IR) spectra of the Compton-thick Seyfert 2 galaxy NGC 3281, obtained with the Thermal-Region Camera Spectrograph at the Gemini-South telescope. The spectra present a very deep silicate absorption at 9.7 {mu}m, and [S IV] 10.5 {mu}m and [Ne II] 12.7 {mu}m ionic lines, but no evidence of polycyclic aromatic hydrocarbon emission. We find that the nuclear optical extinction is in the range 24 mag {<=} A{sub V} {<=} 83 mag. A temperature T = 300 K was found for the blackbody dust continuum component of the unresolved 65 pc nucleus and the region at 130 pc SE, while the region at 130 pc NW 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{sub 0}/R{sub d} = 20, with 14 clouds in the equatorial radius with optical depth of {tau}{sub V} = 40 mag. We would be looking in the direction of the torus equatorial radius (i = 60{sup 0}), which has outer radius of R{sub 0} {approx} 11 pc. The column density is N{sub H} {approx} 1.2 x 10{sup 24} cm{sup -2} and the iron K{alpha} equivalent width ({approx}0.5-1.2 keV) is 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 active galactic nucleus torus.
- OSTI ID:
- 21582863
- Journal Information:
- Astrophysical Journal, Vol. 738, Issue 1; Other Information: DOI: 10.1088/0004-637X/738/1/109; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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