EDP Sciences
Free Access
Volume 391, Number 2, August IV 2002
Page(s) L21 - L24
Section Letters
DOI https://doi.org/10.1051/0004-6361:20021039

A&A 391, L21-L24 (2002)
DOI: 10.1051/0004-6361:20021039


NGC 5506 unmasked as a Narrow Line Seyfert 1:

A direct view of the broad line region using near-IR spectroscopy
N. M. Nagar1, E. Oliva1, 2, A. Marconi1 and R. Maiolino1

1  INAF, Arcetri Observatory, Largo E. Fermi 5, Florence 50125, Italy
2  INAF, Telescopio Nazionale Galileo, Aptdo de Correos, 565, 38700 Santa Cruz de La Palma, Canary Islands, Spain

(Received 12 May 2002 / Accepted 13 July 2002)

This letter presents incontrovertible evidence that NGC 5506 is a Narrow Line Seyfert 1 (NLSy1). Our new 0.9-1.4  $\mu$m spectrum of its nucleus clearly shows the permitted $\ion{O}{I}$ $\,\lambda 1.1287~\mu$m line (with full width at half maximum <2000 km s -1) and the "1 micron $\ion{Fe}{II}$ lines". These lines can only originate in the optically-thick broad line region (BLR) and, among Seyfert nuclei the latter series of lines are seen only in NLSy1s. The obscuration to the BLR, derived from a rough estimate of the $\ion{O}{I}$ $\,\lambda 1.1287~\mu$m/ $\ion{O}{I}$ $\,\lambda$8446 ratio and from the reddening of the near-IR Paschen lines, is $A_{\rm V}\,>\,5$. Together, these results make NGC 5506 the first identified case of an optically-obscured NLSy1. This new classification helps explain its radio to X-ray properties, which until now were considered highly anomalous. However, interesting new concerns are raised: e.g., NGC 5506 is unusual in hosting both a "type 1" AGN and a nuclear water vapor megamaser. As the brightest known NLSy1, NGC 5506 is highly suitable for study at wavebands less affected by obscuration.

Key words: line: formation -- line: identification -- galaxies: active -- galaxies: individual: NGC 5506 -- galaxies: Seyfert -- galaxies: infrared

Offprint request: N. Nagar, neil@arcetri.astro.it

© ESO 2002