Dense gas in nearby galaxies. II. CS emission from spiral galaxies.

A search for the CS J=2-1 and 3-2 transitions, which trace out high density (n(H_2_)>= 10^4^ cm^-3^) gas, is reported for 12 galaxies known to be strong CO emitters. Detections were obtained for Maffei 2, NGC4945, M83, and NGC6946; there are marginal detections toward the Seyfert galaxy NGC 1068 and toward NGC 3079, which increase the total number of galaxies observed in CS from three to seven or nine. The CS(3-2) emission toward NGC 6946 is unresolved by a 16" beam. From upper limits of the CS(5-4) emission toward Maffei 2 and NGC 6946, upper limits (10^5^ cm^-3^) to the hydrogen number density are obtained. For the sources with (marginally) detected 3-2 emission, the CS(3-2)/CO(1-0) intensity ratio lies in the range between 1:15 and 1:68. For M51, we obtain 1:>80. There appears to be a relationship between the IR luminosity and the CS/CO intensity ratio (a measure of the relative abundances of high and low density gas), indicating that the fraction of high density gas becomes large in nuclei with a high star forming rate. A correlation between the dust temperature and the CS(3-2)/CO(1-0) intensity ratio is not apparent.