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Astron. Astrophys. 329, L21-L24 (1998)


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Letter to the Editor

Spectropolarimetry of the Circinus galaxy *

E. Oliva 1, A. Marconi 1, 2, 3, A. Cimatti 1 and S. di Serego Alighieri 1

1 Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5, I-50125 Firenze, Italy
2 Dipartimento di Astronomia e Scienza dello Spazio, Largo E. Fermi 5, I-50125 Firenze, Italy
3 Present address: Space telescope Science Institute, 3700 S. Martin Drive, Baltimore 21218 MD, USA

Received 5 September 1997 / Accepted 25 September 1997

Abstract

High quality 4500-6800 Å spectropolarimetric observations of the Circinus galaxy are reported. These show polarized and relatively broad (FWHM [FORMULA] 3300 km/s) H [FORMULA] (as well as marginal H [FORMULA]) arising from a [FORMULA] 3" ([FORMULA] 60 pc) region centered on the nucleus and coincident with the the peak of the narrow line region. Broad H [FORMULA] might also be present [FORMULA] 8" (160 pc) SE from the nucleus and close to the dust lane, but the result is only marginal and should be verified by higher s/n data. The continuum is dominated by stellar emission with [FORMULA] 3% contribution from the scattered AGN continuum, and all the light (i.e. all the stellar continuum and narrow lines) is polarized, most probably by transmission through and scattering by dust in the disk. The data are compatible with a simple model where the scattered broad lines and AGN emission are quite polarized (P [FORMULA] 25%) but account for only 1% of the observed continuum. The scattered broad H [FORMULA] has an equivalent width W [FORMULA] [FORMULA] 400 Å, a flux similar to the narrow H [FORMULA] and a luminosity [FORMULA] 5 [FORMULA] [FORMULA]. Assuming an efficiency of 1% for the BLR mirror, the intrinsic luminosity of the broad H [FORMULA] is roughly [FORMULA] [FORMULA] and [FORMULA] 0.5% of the FIR luminosity, a ratio similar to those found in type 1 Seyferts. Specific prediction for future observations are also presented.

Key words: galaxies: Seyfert – galaxies: individual: Circinus

* Based on observations collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: E. Oliva

© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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