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 H α and H β . After removal of narrow emission lines (NELs), the full width at half maximum (FWHM) of the Lorentzian BEL is <?CDATA ${\mathrm{FWHM}}_{\mathrm{BEL}}$?> ≈ 1270 <?CDATA $\mathrm{km}\,{{\rm{s}}}^{-1}$?> , 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 ( <?CDATA $g-{W}_{4}=13.172$?> 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 ( <?CDATA ${\mathrm{FWHM}}_{\mathrm{Polarized}\mathrm{BEL}}\approx 1183$?> <?CDATA $\mathrm{km}\,{{\rm{s}}}^{-1}$?> ), with a high polarization degree of &gt;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 <?CDATA ${M}_{\bullet }\lt 2.9\times {10}^{7}\,{M}_{\odot }$?> and <?CDATA ${L}_{\mathrm{bol}}/{L}_{\mathrm{Edd}}\gt 1.5$?> . 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.