Constraints on the nuclear emission of the Circinus galaxy: optical and near-IR spectropolarimetry(star)

We present optical and, for the first time, K-band spectropolarimetry of th e nuclear region of the Circinus galaxy. In the optical we confirm the prev ious discovery of polarized broad H alpha. We have not detected polarized b road Br gamma in the K band, however we can place a 3 sigma upper limit of 7 x 10(-15) erg s(-1) cm(-2.) This corresponds to an upper limit of 7.7 mag of visual extinction along the broad-line scattered route assuming electro n scattering and the Case B approximation. Analysis of these observations shows that galactic processes dominate in th e optical total and polarized flux whilst the nucleus dominates the K-band polarized flux. From a sample of Seyfert 1 galaxies we find a tight non-ste llar R-band continuum to broad H alpha correlation that allows us to constr ain the nuclear continuum contribution at optical wavelengths. Based on the se constraints we have modelled our observations as electron scatterers dis tributed in a 50 degrees inclined cone of 45 degrees opening half-angle, vi sually extincted by 5 mag through the Galaxy and Circinus galactic disc. At near-IR wavelengths the nuclear emission region becomes visible and dichro ically polarized through the dusty torus; we find a visual extinction to th is region of 35 mag gives the best results, consistent with that determined using other techniques. A comparison of the [O III]lambda 5007 emission line and infrared luminosit y to other Seyfert 2 galaxies shows that the Circinus galaxy is the lowest powered object for which broad lines have been detected in polarized flux. As it is the closest Seyfert 2 galaxy to us this suggests considerable diff iculty in finding polarized broad lines in other low-powered obscured AGN.