1 Introduction

Seyfert galaxies are divided into two main classes according to their optical properties. The main difference being that type 1 Seyferts (Sy1s) exhibit a broad line region, in addition to the narrow line region, which is evident in both the classes. According to the currently favoured scenario, the Seyfert nucleus is surrounded by a dusty torus shaped region and the observed properties are determined solely by the orientation of the torus relative to the observers line of sight to the nucleus (Antonucci 1993). In type 1 nuclei, the axis of the torus is close to the line of sight and one observes a naked AGN directly with its associated broad line region in full view. In type 2 nuclei, the orientation of the dusty torus is such that it shields the nucleus from view and only the more extended narrow line clouds are observed. It is not clear what difference this would make to the observed molecular properties of the galaxies; for the Sy2 galaxy NGC 4258 the CO is widely distributed and appears to have no connection to the nuclear activity. Contrary to this, Heckman et al. (1989) have found that in Sy2s, the observed ratio of the CO luminosity, $L_{\rm CO}$, as a fraction of the blue luminosity, is a factor of two greater than for Sy1s. An enhanced CO/blue luminosity ratio in Sy2s is also observed by Sahai et al. (1991). Since most of the blue continuum is generally believed to emanate from the accretion disc (e.g. Peterson 1997), which is obscured in Sy2s, these studies have possibly failed to take into account the fact that, on average, the Sy2s selected on this basis will tend to be more luminous than the Sy1s. In this paper we test their results by comparing the CO luminosities with respect to the far infrared (FIR) luminosities, as the latter quantity is expected to be a more isotropic parameter than the blue luminosity.

Another possible distinction between the two main Seyfert classes is the fact that, as well as the difference in orientation of the dusty obscuring torus, there may exist differences on how the molecular gas is distributed. While McLeod & Rieke (1995); Maiolino & Rieke (1995) find that the galactic disc is aligned with the pc-scale molecular ring (Sy2 nuclei tend to lie in edge-on galaxies and Sy1s in face-on systems), they find that Sy1 nuclei may be partially obscured by the ring, which could be misaligned with the pc-scale obscuring torus. However, Wilson & Tsvetanov (1994); Capetti et al. (1996) find that the axis of the ionisation cone, coincident with the axis of the obscuring torus which collimates the ionised outflow (Antonucci & Miller 1985; Wilson et al. 1988; Tadhunter & Tsvetanov 1989; Wilson & Tsvetanov 1994; Baker & Scoville 1998), also tends to be aligned with the host galaxy disc axis, thus placing the disc coplanar with the torus.

In this paper we use the observational results of the Northern and Southern Seyfert survey of Curran et al. (2000) in order to test the two main points outlined above, namely:

1.

Statistical studies of the difference in dense gas abundances between type 1 and type 2 Seyferts.

2.

Differences in the aspect of the gas distribution between type 1 and type 2 Seyferts.