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

Xiang Pan, Honglin Lu, S. Komossa, Dawei Xu, Weimin Yuan, Luming Sun, Paul S. Smith, Shaohua Zhang, Peng Jiang, Chenwei Yang, Wenjuan Liu, Ning Jiang, Y. E. Rashed, A. Eckart, Jens Dierkes, Hongyan Zhou

Published 2018-11-16, updated 2019-10-11Version 2

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 of the lorentzian BEL is $FWHM_{\rm BEL} \approx 1,270$ 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 1AGNs. This, together with its large MIR excess ($g-W_4 = 13.172$ mag), implies that the observer and the narrow emission line region (NELR) might see a different ionization continuum. Our optical spectropolarimetry confirms its type 2 nature by detecting a polarized blue continuum and Balmer BELs ($FWHM_{\rm Polarized~BEL} \approx 1,183$ km s$^{-1}$), with a high polarization degree of $> 20$% in the blue wing. The mass and Eddington rate of the central black hole is estimated based on both transmitted and scattered AGN radiation, which is $M_{\bullet} < 2.9 \times 10^7 M_\odot$ and $L_{\rm bol}/L_{\rm Edd} > 1.5$. Severe extinction of the AGN emission also enables a clear view of the compact host galaxy. Discovery of J1203+1624 suggests that NLS1 follows AGN unfication scheme, studying of its analogs could blaze a new trail for exploring the connection between black hole growth and star formation in the host galaxy. Interesting features of J1203+1624 like the peculiar NELs, inflowing scattering clouds within sublimation radius are worth detailed follow-ups in the future.