期刊
ASTRONOMY & ASTROPHYSICS
卷 391, 期 2, 页码 L21-L24出版社
E D P SCIENCES
DOI: 10.1051/0004-6361:20021039
关键词
line : formation; line : identification; galaxies : active; galaxies : individual : NGC 5506; galaxies : Seyfert; galaxies : infrared
This letter presents incontrovertible evidence that NGC 5506 is a Narrow Line Seyfert 1 (NLSy1). Our new 0.9-1.4 mum spectrum of its nucleus clearly shows the permitted OI lambda1.1287 mum line (with full width at half maximum <2000 km s(-1)) and the 1 micron 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 OIλ1.1287 μm/OIλ8446 ratio and from the reddening of the near-IR Paschen lines, is A(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.
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