2 Observations

We have observed the CO $1\rightarrow 0$ (115 GHz) and HCN  $1\rightarrow 0$ (88.6 GHz) lines in a sample of 20 Seyfert galaxies. The Southern sample was observed in December 1997 and October 1998 with the 15 m SEST at La Silla, Chile. Since the 100 GHz and 115 GHz can be used simultaneously with the 150 GHz and the 230 GHz receivers, respectively, we also observed CS  $3\rightarrow2$ (147 GHz) and CO $2\rightarrow 1$ (230 GHz). All receivers were tuned to the single-band mode and typical system temperatures, on the $T_{\rm A}^*$-scale, were 150 K at 89 GHz, 200 to 300 K at 115 GHz, 200 K at 150 GHz and 300 K at 230 GHz. The HPBWs are 57'', 45'', 34'', and 22'', respectively. The backends were acousto-optical spectrometers with 1440 channels and a channel width of 0.7 MHz. We used dual-beam switching with a throw of about $12\hbox{$^\prime$ }$ in azimuth, with pointing errors being typically $3\hbox{$^{\prime\prime}$ }$ rms on each axis. The intensity was calibrated using the chopper-wheel method. For the first observing run the weather was excellent, and only the removal of linear baselines was required. However, two of the sources, NGCs 6814 and 7130, were within the sun-limit and, after the application for more time, were observed during the second run under similarly good conditions.

 

 

Table 1: Beam sizes and efficiencies

Transition	$\nu$ [GHz]	HPBW ['']		$\eta _{\rm mb}$
		OSO	SEST	OSO	SEST
HCN  $1\rightarrow 0$	89	44	57	0.59	0.75
CO  $1\rightarrow 0$	115	33	45	0.50	0.70
CS  $3\rightarrow2$	147	-	34	-	0.66
CO  $2\rightarrow 1$	230	-	22	-	0.50

The Northern sample was originally observed in February 1998 with the 20 m telescope at Onsala Space Observatory (OSO). During this session, however, the weather was unfavourable and more time was awarded for the following November. Both the CO $1\rightarrow 0$ and HCN  $1\rightarrow 0$ transitions were observed with the SIS 100 GHz receiver. The HPBWs are 33'' and 44'', respectively. The backend was a filter-bank with a bandwidth of 512 MHz and a channel separation of 1 MHz. We used a similar dual-beam switching as the SEST observations and obtained similar pointing errors. Although far from ideal for most of the session, the weather was a great improvement over the previous run, with HCN being observed when the weather was poorest. Typical system temperatures were around 500 K for CO. This is considerably worse than the optimal 300 K, but given the improved receivers, is comparable with the system temperatures of Heckman et al. (1989). Some of the Northern sources were re-observed in April 1999 when the excellent weather gave system temperatures of $\approx230$ K and $\approx350$ K for the HCN and CO lines, respectively. As with the SEST data, only linear baselines were removed.