NGC 5506 unmasked as a narrow line Seyfert 1: A Direct view of the broad line region using near-ir spectroscopy

摘要: This letter presents incontrovertible evidence that NGC 5506 is a Narrow Line Seyfert 1 (NLSy1). Our new 0.9–1.4  μ m spectrum of its nucleus clearly shows the permitted $\ion{O}{I}$ $\,\lambda 1.1287~\mu$m line (with full width at half maximum -1 ) and “1 micron $\ion{Fe}{II}$ lines”. These lines can only originate in optically-thick broad line region (BLR) and, among nuclei latter series are seen NLSy1s. The obscuration to BLR, derived from rough estimate 1.1287~\mu$m/$\ion{O}{I}$ $\,\lambda$8446 ratio reddening near-IR Paschen lines, $A_{\rm V}\,>\,5$. Together, these results make first identified case an optically-obscured NLSy1. classification helps explain radio X-ray properties, which until now were considered highly anomalous. However, interesting concerns raised: e.g., unusual hosting both “type 1” AGN nuclear water vapor megamaser. As brightest known NLSy1, suitable for study wavebands less affected by obscuration.