THE COMPTON-THICK SEYFERT 2 NUCLEUS OF NGC 3281: TORUS CONSTRAINTS FROM THE 9.7 mu m SILICATE ABSORPTION

Author(s)

Sales, Dinalva A. ^[1] ; Pastoriza, M. G. ^[1] ; Riffel, R. ^[1] ; Winge, C. ^[2] ; Rodriguez-Ardila, A. ^[3] ; Carciofi, A. C. ^[4]

Affiliation

^[1] Univ Fed Rio Grande do Sul, Dept Astron, Porto Alegre, RS - Brazil

^[2] AURA Inc, Gemini Observ, La Serena - Chile

^[3] MCT, Lab Nacl Astrofis, Itajuba, MG - Brazil

^[4] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Sao Paulo - Brazil

• Document type: Journal article
• Source: ASTROPHYSICAL JOURNAL; v. 738, n. 1 SEP 1 2011.
• Web of Science Citations: 19

Abstract

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(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(0)/R(d) = 20, with 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 = 60 degrees), which has outer radius of R(0) similar to 11 pc. The column density is N(H) approximate to 1.2 x 10(24) cm(-2) and the iron K alpha equivalent width (approximate to 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. (AU)

• FAPESP's process: 10/19029-0 - 3D radiative transfer models: bridging theory and observations
• Grantee: Alex Cavaliéri Carciofi
• Support type: Regular Research Grants