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

Abstract

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 Hα and Hβ. After removal of narrow emission lines (NELs), the full width at half maximum (FWHM) of the Lorentzian BEL is ≈ 1270 , 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 ( 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 ( ), 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 and . 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.