A Deeply Buried Narrow-line Seyfert 1 Nucleus Uncovered in Scattered Light

Abstract

We present spectropolarimetric and spectrophotometric observations of the peculiar active galactic nucleus (AGN) SDSS J120300.19+162443.7 (hereafter J1203+1624) at z = 0.1656. Its optical total flux spectra clearly show broad emission lines (BELs) in H alpha and H beta. After removal of narrow emission lines (NELs), the full width at half maximum (FWHM) of the Lorentzian BEL is FWHMBEL approximate to 1270 km s(-1), fulfilling the conventional definition of a narrow-line Seyfert 1 (NLS1) galaxy. However, its NELs are unprecedentedly strong when compared to type 1 AGNs. This, together with its large MIR excess (g - W-4 = 13.172 mag), implies that the observer and the NEL region might see a different ionization continuum. Our optical spectropolarimetry confirms its type 2 nature by detecting a polarized blue continuum and Balmer BELs (FWHMPolarized BEL approximate to 1183 km s(-1)), with a high polarization degree of > 20% in the blue wing. The mass and Eddington rate of the central black hole are estimated based on both transmitted and scattered AGN radiation, which is M-center dot < 2.9 x 10(7) M-circle dot and L-bol/L-Edd > 1.5. Severe extinction of the AGN emission also enables a clear view of the compact host galaxy. The discovery of J1203 +1624 suggests that NLS1 follows the AGN unification scheme, and studying its analogs could blaze a new trail for exploring the connection between black hole growth and star formation in the host galaxy. The interesting features of J1203+1624, like the peculiar NELs and inflowing scattering clouds within the sublimation radius, are worth detailed follow-ups in the future.