3 Observational results

 

  

Table 3: CS and C³⁴S line areas and Gaussian line parameters at the indicated positions of the sources. The numbers in the brackets are the statistical uncertainties in the last digits (standard deviations). The upper limits represent the 3$\sigma$ values ($\sigma$ is rms noise in channels)

  

Figure 1: Histograms of the CS integrated line intensity distributions for the present Onsala sample and for the SEST sample from Paper I

We detected 47 CS emitting cores in total associated probably with 50 masers. No CS emission was found towards 5 masers. The C³⁴S emission was detected in 19 of these cores (some of them just have not been observed in the C³⁴S line). In addition, C³⁴S was detected in NGC 281. So the CS detection rate is comparable to that achieved at SEST (Paper I). However, the CS emission for the present sample is in general much weaker than for the SEST sample. This fact is illustrated by Fig. 1 where we plot the histograms of the integrated line intensity distributions for both samples in the same temperature scale. The possible influence of the difference in the beam size could only smoothen the difference in the line intensities. It is worth noting that the average distances to the sources in both samples are similar.

The sources studied in the present work are located in the outer Galaxy while most SEST sources belong to the inner Galaxy. Thus, Fig. 1 clearly shows a difference between them.

Due to the relative weakness of these sources we were unable to obtain the same set of data for each source as in Paper I. Only for about a third of the detected cores (15) do we have a comparable amount of data (reasonably complete CS map, C³⁴S and CO observations near the peaks). We shall refer to these sources as sources of category I. For 11 other cores the CS maps can be considered to be complete, but an absence or low quality of the C³⁴S data do not enable us to estimate masses and densities in the same way as for the first category sources. These objects will be referred to as sources of category II. For the remaining 21 sources (category III) the data are incomplete and we cannot derive sizes, masses, virial masses and densities. The physical information obtained for these sources comprises mostly the kinetic temperature (from the CO brightness), velocity dispersion (from the line widths) and kinematic distance.

In Table 3 we present the CS and C³⁴S integrated line intensities and Gaussian line parameters for detected sources. These data refer either to the grid positions closest to the CS emission peaks or to the (0,0) positions. A typical rms noise for non-detected sources is $\sim$0.1-0.2 K in 250 kHz channels.

For the sources of the categories I and II we present also the CS maps and the CO, CS and, when available, C³⁴S spectra at the indicated positions (Fig. 2).

  

Figure 2: Left panels: the integrated CS line intensity maps for the sources of categories I and II (see text). The levels start from 15% of the peak intensities in steps of 7.5%. The peak intensities are nearly equal to those presented in Table 3. Crosses mark the IRAS positions. Triangles indicate water masers. Right panels: CO, CS and C34S spectra at the indicated positions

  

Figure 2: continued

  

Figure 2: continued

  

Figure 2: continued