Based on results collected at the European Southern Observatory, La Silla, Chile and Onsala Space Observatory, Sweden.

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These galaxies were chosen on the grounds that they provide a good sample of Seyferts. As well as this, they constitute the same sample of Heckman et al. (1989), thus enabling us to also test their finding that type 2 Seyferts have higher molecular gas abundances than type 1s (see Curran 2000b and Paper II).

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... near-by

Galaxies where $$v\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil $\displaystyle ...$ km s^-1.

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... 6814

Note that since we failed to detect HCN in NGCs 5347 and 7172 (Curran et al. 2000), we will not include these sources in this work.

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... SEST

The Swedish-ESO Sub-millimetre Telescope is operated jointly by ESO and the Swedish National Facility for Radio Astronomy, Onsala Space Observatory, Chalmers University of Technology.

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... mapped

For example, although HCN $1\rightarrow 0$ is mapped to $68''\times 68''$ in NGC 1365 (Fig. 2), the HPBW of 57'' increases this to $$\mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil $\displaystyle ...$ due to the beam extending beyond the "mapped region''.

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... size

Obtained by assuming that the source distribution on the sky is Gaussian and deconvolving the telescope response (HBPW) from the full-width half-maximum (FWHM) diameter, e.g. Dahlem et al. (1993). The source sizes are tabulated and discussed in Paper II.

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... beam

In the angular size of the corresponding transition, Table 1.

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... HCN

From now on, unless otherwise stated, HCN or CO refers to the $1\rightarrow 0$ transition for the appropriate molecule.

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... molecule

The detection of Curran et al. (2000) was new.

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...)

Where all of the molecular gas is expected to be contained within the central beam (Sect. 1). For example, Young et al. (1995) obtain the same value of $L_{\rm CO~1\rightarrow0}$ in an area which is twice the diameter of our beam (at OSO), thus confirming this (see previous section).

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