1 Introduction

The Seyfert nucleus of NGC 5506 has resisted a clear type classification within Seyfert galaxies, and there is a long standing debate on whether it is an intermediate type 1 (broad H$\alpha$ directly visible) or type 2 (broad H$\alpha$ not directly visible) Seyfert. The presence of "broad'' Pa$\beta$ has been reported by Blanco et al. (1990), Rix et al. (1990), and Ruiz et al. (1994), but Goodrich et al. (1994) found that the "narrow'' line emission profiles become broader at longer wavelengths and suggested that the "broad'' Pa$\beta$ was the strong, highly reddened wings of this profile. Based on data available at that time Goodrich et al. (1994) interpreted the broadening of emission lines with wavelength as due to obscuration of the inner parts of the narrow line region. Morris & Ward (1985) reported a marginal detection of O I$~\lambda$8446, characteristic of Seyfert 1s, and suggested the presence of high-density optically thick gas. At odds with other type 2 objects, the nucleus of NGC 5506 is dominated by a bright compact core at all near-IR wavelengths and 60% of the J-band (1.25 $\mu$m) flux in its central few arcsec is non-stellar in origin (Oliva et al. 1999; Alonso-Herrero et al. 2001). In the hard X-ray it is one of the most luminous and brightest Seyferts in the local universe ( $L_{\rm 2-10~keV}\sim 10^{43}$; Mushotzky 1982) and its obscuring column ($N_{\rm H}$ $~= 3.4~\times~10^{22}$ cm^-2; Bassani et al. 1999) is intermediate between typical values for Seyfert 1s and 2s. Nuclear water vapor masers, a property highly correlated with a type 2 spectral classification (Braatz et al. 1996), have been detected towards its nucleus (Braatz et al. 1994).

The host galaxy causes additional complications. The galaxy disk is close to edge on ( $i~=~70{\hbox{$^\circ$ }}$), and dust in the galaxy disk is responsible for some or all of the nuclear reddening (Veilleux et al. 1997; Imanishi 2000). NGC 5506 is therefore variously treated as a type 1.9 or type 2 Seyfert in the literature and in either case is usually an outlier among the members of its class.

In this letter we report on near-IR spectroscopy of NGC 5506, which unequivocally identifies it as a Narrow Line Seyfert 1 (NLSy1). In a NLSy1 the broad line region (BLR) is directly visible with the BLR emission lines having widths typically $\leq$2000 km s^-1, significantly narrower than those in classical Seyfert 1s. NLSy1s show several anomalous properties, most notably in the X-ray (for a nice overview of these see Véron-Cetty et al. 2001) and explanations for these include accretion rates close to the Eddington rate (implying lower black hole masses than other Seyferts) or a view to the AGN along its axis.