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

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3. Results

In Fig. 1, we show the spectra obtained toward 29 external galaxies. For the presentation, the resolution of the spectrometer has been degraded to 6.7 km s-1, only for IC 10 it is 3.8 km s-1. We have detected line emission toward all sources. For most of these sources, this is the first time that [FORMULA] data are published. Even for Centaurus A, which at Mount Graham never rises higher than [FORMULA], a high quality baseline and repeatable line profiles and line intensities were obtained. From the data, we have determined the line flux, [FORMULA], and we have estimated the line width and the radial velocity using either Gaussian fits to the lines, or, in the case of non-Gaussian lineshapes, giving the first or second moments of the spectra. Results as well as intensities of the 1-0 and 2-1 lines, which were observed by us or taken from published 30-m data, are given in Table 1. In Table 2, we summarize important source parameters together with the flux ratio of the 12CO 3-2 and 1-0 lines.

[FIGURE] Fig. 1. 12CO [FORMULA] spectra. The velocity scale corresponds to the Local Standard of Rest. Intensities are in K (main-beam brightness temperature)


Table 1. Line parameters of detected [FORMULA]
a) from Gaussian fit to the 3-2 line.
b) in the case of non-Gaussian profiles, the line flux and the median velocity and widths are computed from the moments.
c) All [FORMULA] and 2-1 data are from the 30-m telescope.
NGC 2146, NGC 2964, NGC 3079, NGC 3351, NGC 3368, NGC 4414, NGC 5907, NGC 6217, NGC 7331: Braine et al. (1993); IC 10: Becker (1990); NGC 891: García-Burillo et al. (1992); Maffei 2, NGC 6946: Weliachew et al. (1988); IC 342: Eckart et al. (1990); NGC 2903: Jackson et al. (1991); Arp220: Solomon et al. (1990), Jackson et al. (1991); NGC 3627: Reuter et al. (1996), NGC 3628: Reuter et al. (1991), Boisse et al. (1987); NGC6000: Chini et al. (1996); data based on own measurements at the 30 m telescope are given in italics.


Table 2. Properties of the observed galaxies
a) [FORMULA] computed from the 60 and 100 µm IRAS fluxes and assuming an emissivity that is proportional to [FORMULA], [FORMULA] using IRAS data.
b) if not otherwise noted: Tully (1988); IC 10: Wilson et al. (1996); Maffei 2, IC 342: McCall (1989); NGC 6946: Karachentsew & Sharina (1997)
c) From data obtained by Harrison et al. (1998) with the 30-m telescope and the Caltech Sub-mm Telescope.

In general, there is good agreement between shapes and intensities of our observed lines and other [FORMULA] data (see the Appendix). Data taken in April 1998 at our positions with the same setup (R. Wielebinski, pers. comm.) show virtually identical calibration scales for M 82, M 83, IC 342, NGC 2146, NGC 3351 and NGC 5907. For NGC 3627, NGC 3628 and M 51 these data show a 30% higher intensity, and for NGC 3079 a 30% lower intensity. Such differences are compatible with our estimate of the calibration errors and with the uncertainties from the fits to the line profiles.

Our literature search made clear that the application of correct calibration schemes cannot be taken for granted in all cases. In order to present a sample that is as homogeneous as possible, we therefore restrict our comparison to CO 1-0 and 2-1 data which have been measured using the IRAM 30-m telescope. In Fig. 2 we show the velocity integrated relative intensities of the three lowest CO transitions, normalized to the CO 1-0 transition.

[FIGURE] Fig. 2. The integrated intensity, [FORMULA] in K km s-1 of the three lowest CO lines. The [FORMULA] and 2-1 data are from Braine et al. (1993) normalized to the 1-0 line. For completeness, data from NGC 253 obtained at the IRAM 30-m telescope and the JCMT (Harrison et al., 1998) are also shown. All data refer to a beam of [FORMULA].

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© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998