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Astron. Astrophys. 341, 256-263 (1999)

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Appendix A: Notes on individual sources

IC 10. The observed position is the origin of a strong water maser (Henkel et al., 1986). Here, the 3-2 line is much weaker than 1-0 in the 21" beam of the 30-m telescope (Becker, 1990). CO 3-2 has been recently observed by Petitpas & Wilson (1998). For two positions they report [FORMULA] ratios of 0.3-0.5, which is slightly higher than the line ratio we find at a different position.

Maffei 2. This galaxy has been mapped in CO 1-0 by Weliachew et al. (1988) with 23" resolution and in the 3-2 line by Hurt et al. (1993) with a resolution of 22". Our spectrum shows the characteristic double profile, which is also seen in other transitions. There seem to be inconsistencies in the paper by Hurt et al. (1993) concerning their calibration, which also should influence their conclusions: While they claim that the [FORMULA] ratio inferred from the data of Weliachew et al. (1988) is close to unity, Fig. 5 of Hurt et al. (1993) suggests a value closer to 2. If our calibration is correct, the [FORMULA]/1-0 intensity ratio is close to unity.

IC 342. There have been numerous molecular line observations of this nearby spiral. Observations of interstellar ammonia (Martin & Ho (1986)) suggest a kinetic temperature [FORMULA]. An HCN map by Downes et al. (1992) shows a number of dense clumps of typically 20-30 pc in diameter. The free-free emission is mainly associated with clump B. Our observation of the 12CO [FORMULA] line was taken toward this clump. The integrated intensity measured by us (138 K km s-1) is within the estimated calibration errors of published CO [FORMULA] measurements (Irwin & Avery 1992: 111 K km s-1 in a 15" beam, Steppe et al. 1990: 165 K km s-1 within a convolved beam of 19", Wall et al. 1991: 139 K km s-1 in a 15" beam).

NGC 2146. We have used the same coordinates as Braine et al. (1993) and as Devereux et al. (1994). Our line shape resembles that of Braine et al. obtained with a 23" beam in the CO [FORMULA] and 1-0 lines. Devereux et al. (1994) observe a much smaller linewidth in the 3-2 and 1-0 line with a 14" beam. We are probably seeing a more extended gas component than Devereux et al. (1994), or there is a mispointing in the Devereux et al. data.

M 82 (NGC 3034). In the past, there have been claims of CO [FORMULA] ratios of [FORMULA] toward the center of M 82 due to optically thin CO emission. In Fig. A1, we show the profiles of the first three transitions of 12CO convolved to a 21" beam. Line intensity ratios are close to one. The 1-0 and 2-1 profiles were produced from simultaneously made [FORMULA] point maps with 5" spacing. The IRAM data were shifted so that the profiles matched the profiles of the 3-2 line. This was achieved at a nominal [FORMULA] for the 2-1 line and 3" for the 1-0 line. Note that due to the steep velocity gradients in the central region of M 82 the profile changes drastically with position shifts of just 2 or 3". This has to be borne in mind when comparing data from different telescopes or different transitions or molecules. Like in other starburst galaxies, we find 2-1/1-0 and 3-2/1-0 intensity ratios close to unity.

[FIGURE] Fig. A1. The [FORMULA] (dashed lines), 2-1 (solid lines) and 3-2 (histogram) profiles of 12CO toward the center of M 82. All spectra were convolved to a beam size of 21" and the nominal origins of the 1-0 and 2-1 profiles were shifted slightly until their shape matched that of the 3-2 line. The temperature scale is [FORMULA].

NGC 3351 (M 95). The line shape of the 3-2 line is much more asymmetrical than that of the 2-1 and 1-0 spectra by Braine et al. (1993), indicating a possible mispointing of our data. The CO profiles exhibit a pronounced double peak. The blue-shifted peak at 700 km s-1 is much stronger in CO 3-2 than in lower lying CO transitions. This indicates that it arises off-center perhaps coinciding with an optical ring (Jackson et al., 1989).

NGC 3627 and NGC 3628. The positions measured are offset from the central positions. Intensities of the 1-0 and 2-1 lines are taken at our 3-2 positions from the maps by Reuter et al. (1991, 1996). CO 3-2 intensities toward the centers of the galaxies are [FORMULA] times higher than at the positions observed by us (R. Wielebinski, priv. comm.).

NGC 4818. With a 14" beam, Devereux et al. (1994) observed an integrated intensity, [FORMULA], of 60 K km s-1 in the 3-2 line, while we see only 20 K km s-1 in our 21" beam. Presumably, the source we are observing is small compared to our beam, or there are pointing deviations.

Cen A (NGC 5128). This elliptical galaxy contains a dust lane, which is also seen in CO. Toward the center, many molecular lines are seen in absorption. We do see emission, but no signs of absorption as in the CO 3-2 spectrum by Israel et al. (1991). This is due to the fact that we were using the coordinates in Paglione et al. (1997) which are offset from the continuum source by [FORMULA], about one beam width off-center. Our profile looks similar to that of 13CO [FORMULA] taken with the SEST at that position (Wild et al., 1997).

M 51 (NGC 5194). The spectrum was observed toward the dynamic center of M 51. The integrated intensity is comparable to that of the [FORMULA] line (Garcia-Burillo et al., 1993). [FORMULA] ratios close to 1 were found toward many off center positions of this spiral (Bash et al., 1990).

M 83 (NGC 5236). This galaxy has been mapped by Handa et al. (1990) with a 16" beam in the CO 1-0 line. The lineshape is in good agreement with our data.

Arp 220 (IC 4553/4). The CO 3-2 line is similar in intensity to the 1-0 line measued by Radford et al. (1991). It is also consistent with the CO 2-1 in Rigopoulou (1996). Note that the intensities in Table 2 of that publication are given in antenna temperature and not, as stated, in main-beam brightness temperature (D. Rigopoulou, priv. comm.). However, the 3-2 line is double peaked, whereas the 1-0 and 2-1 lines from filled aperture observations show a single maximum. A recent interferometer map in CO 2-1 also reveals a double peak structure arising from a compact ([FORMULA]), molecular source (Scoville et al., 1997). Possibly the 1-0 and 2-1 single dish data trace a more smoothly distributed or more extended medium while the 3-2 is mainly seen from fewer clumps with high excitation within the compact molecular disk. It is interesting that in our data the redshifted peak is of higher intensity than the blueshifted one, while in the Scoville et al. (1997) data the blueshifted peak is stronger. Whether this is an excitation effect or is just caused by the different spatial sampling can be decided by higher resolution observations of the CO 3-2 line.

NGC 7331. The lineshape is different from that of CO 1-0 and 2-1, suggesting a pointing offset.

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© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998
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