THE MID-INFRARED CONTINUA OF SEYFERT GALAXIES

Journal Article · Sun Nov 01 04:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/705/1/14· OSTI ID:21378418

Deo, Rajesh P; Richards, Gordon T ^[1]; Crenshaw, D M ^[2]

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1. Department of Physics, Drexel University, 3141, Chestnut Street, Philadelphia, PA 19104-2816 (United States)
2. Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States)

An analysis of archival mid-infrared (mid-IR) spectra of Seyfert galaxies from the Spitzer Space Telescope observations is presented. We characterize the nature of the mid-IR active nuclear continuum by subtracting a template starburst spectrum from the Seyfert spectra. The long wavelength part of the spectrum contains a strong contribution from the starburst-heated cool dust; this is used to effectively separate starburst-dominated Seyferts from those dominated by the active nuclear continuum. Within the latter category, the strength of the active nuclear continuum drops rapidly beyond approx20 mum. On average, type 2 Seyferts have weaker short-wavelength active nuclear continua as compared to type 1 Seyferts. Type 2 Seyferts can be divided into two types, those with strong polycyclic aromatic hydrocarbon (PAH) bands and those without. The latter type show polarized broad emission lines in their optical spectra. The PAH-dominated type 2 Seyferts and Seyfert 1.8/1.9s show very similar mid-IR spectra. However, after the subtraction of the starburst component, there is a striking similarity in the active nuclear continuum of all Seyfert optical types. PAH-dominated Seyfert 2s and Seyfert 1.8/1.9s tend to show weak active nuclear continua in general. A few type 2 Seyferts with weak/absent PAH bands show a bump in the spectrum between 15 and 20 mum. We suggest that this bump is the peak of a warm (approx200 K) blackbody dust emission, which becomes clearly visible when the short-wavelength continuum is weaker. This warm blackbody emission is also observed in other Seyfert optical subtypes, suggesting a common origin in these active galactic nuclei.

• OSTI ID: 21378418
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 705; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AROMATICS
DUSTS
EMISSION
GALAXIES
GALAXY NUCLEI
HYDROCARBONS
INFRARED SPECTRA
ORGANIC COMPOUNDS
POLYCYCLIC AROMATIC HYDROCARBONS
SEYFERT GALAXIES
SPECTRA
TELESCOPES
WAVELENGTHS