Aims. We study the distribution of the molecular gas in the Andromeda galaxy (M 31) and compare this with the distributions of the atomic gas and the emission from cold dust at λ175 µm. Methods. We obtained a new 12 CO(J = 1−0)-line survey of the Andromeda galaxy with the highest resolution to date (23 , or 85 pc along the major axis), observed On-the-Fly with the IRAM 30-m telescope. We fully sampled an area of 2• × 0.• 5 with a velocity resolution of 2.6 km s −1 . In several selected regions we also observed the 12 CO(2−1)-line. Results. Emission from the 12 CO(1−0) line was detected from galactocentric radius R = 3 kpc to R = 16 kpc with a maximum in intensity at R ∼ 10 kpc. The molecular gas traced by the (velocity-integrated) (1−0)-line intensity is concentrated in narrow arm-like filaments, which often coincide with the dark dust lanes visible at optical wavelengths. Between R = 4 kpc and R = 12 kpc the brightest CO filaments define a two-armed spiral pattern that is described well by two logarithmic spirals with a pitch angle of 7• -8• .The arm-interarm brightness ratio averaged over a length of 15 kpc along the western arms reaches about 20 compared to 4 for H iat an angular resolution of 45 . For a constant conversion factor X CO , the molecular fraction of the neutral gas is enhanced in the spiral arms and decreases radially from 0.6 on the inner arms to 0.3 on the arms at R 10 kpc. The apparent gas-to-dust ratios N(H i)/I 175 and (N(H i) + 2N(H 2 ))/I 175 increase by a factor of ∼20 between the centre and R 14 kpc, whereas the ratio 2N(H 2 )/I 175 only increases by a factor of 4. Conclusions. Either the atomic and total gas-to-dust ratios increase by a factor of ∼20 or the dust becomes colder towards larger radii. A strong variation of X CO with radius seems unlikely. The observed gradients affect the cross-correlations between gas and dust. In the radial range R = 8-14 kpc total gas and cold dust are well correlated; molecular gas correlates better with cold dust than atomic gas. The mass of the molecular gas in M 31 within a radius of 18 kpc is M(H 2 ) = 3.6 × 10 8 M at the adopted distance of 780 kpc. This is 7% of the total neutral gas mass in M 31.

Abstract.We have mapped the CO(3-2) line emission from several nearby galaxies, using the Heinrich-HertzTelescope on Mt. Graham, Arizona. Unlike earlier observations, our investigation is not restricted to starburst galaxies, but includes twelve galaxies of various types and in different stages of star forming activity. Furthermore, we have not only observed the central positions of these objects, but have obtained maps of the extended CO(3-2) emission, with a typical map extent of 2 to 3 arcmin in each direction. Our observations show that this extended mapping is necessary to reveal spatial changes of the ISM properties within the galaxies. In this paper we present the data sets and some data analysis. We compare the galaxies in view of their morphology and excitation conditions, using line ratios, luminosities and other properties, like the extent of the CO(3-2) emission. The main results of this CO(3-2) survey are: 1. In none of the observed objects the emission is confined to the nucleus, as claimed in some earlier publications. CO(3-2) emission can be detected for some objects to the same extent as the CO(2-1) and the CO(1-0) lines. 2. The emission is more concentrated to the vicinity of star forming structures (nuclear regions and spiral arms) than the lower CO transitions for most of the observed objects. This is shown by decreasing (3-2)/(1-0) line intensity ratios from the very centres towards larger radii. The (deconvolved) sizes of the central emission peaks in the CO(3-2) line vary from about 300 pc up to 3 kpc. 3. The CO(3-2) luminosity is stronger in objects that contain a nuclear starburst or morphological peculiarities. The total power emitted in the CO(3-2) line from the central regions (i.e. excluding spiral arms/outer disk) is highest in the starburst galaxies NGC 2146, M 82, NGC 3628, and in the spiral galaxy M 51. When comparing the total power normalized to the size of the emission region, the starburst galaxies M 82 and NGC 253 show the highest values (about three times higher than most other objects), while NGC 278 and NGC 4631 show the lowest. 4. With the present spatial resolution, the line ratios R3,1 seem to be independent of Hubble type, color or luminosity. Most galaxies with enhanced central star formation ("starbursts") show line ratios of the integrated intensities of R3,1 ∼ 1.3 in the very centre and ∼1.0 at a radius of about 1 kpc. Objects with a ring-like (or double-peak if seen edge-on) molecular gas distribution (NGC 253, M 82, and NGC 4631) show lower ratios. The two galaxies that have CO(3-2) emission distributed over their spiral arms (NGC 891 and M 51) show very low line ratios despite their high infrared luminosities. This result suggests that CO emission in these objects reflects a large amount of molecular gas, but not enhanced star forming activity. 5. Starburst galaxies show CO(3-2) emission also in their disks. The line intensities are higher than that of normal galaxies. This suggests that even if a starburst is a localized phenomenon, it is related to different...

Abstract. I present a unique data set for the study of molecular gas in galaxies: a complete, high-resolution survey of the CO in M 31 and additional local studies. The fully sampled survey has an angular resolution of 23" FWHM and the interferometric data attain the pc-scale with subarcsecond resolution. For the first time it is now possible to study large and small scales in conjunction. Thus we are able to derive the global structure and study the links down to the individual cloud complexes and star formation regions.

Abstract. We present a new 12 CO(J=1-0)-line survey of the Andromeda galaxy, M 31, with the highest resolution to date (23 ′′ , or 85 pc along the major axis), observed On-the-Fly with the IRAM 30-m telescope. We mapped an area of about 2 • × 0.• 5 which was tightly sampled on a grid of 9′′ with a velocity resolution of 2.6 km s −1 . The r.m.s. noise in the velocity-integrated map is around 0.35 K km s −1 on the T mb -scale. Emission from the 12 CO(1-0) line is detected from galactocentric radius R = 3 kpc to R = 16 kpc, but peaks in intensity at R ∼ 10 kpc. Some clouds are visible beyond R = 16 kpc, the farthest of them at R = 19.4 kpc. The molecular gas traced by the (1-0) line is concentrated in narrow arm-like filaments, which often coincide with the dark dust lanes visible at optical wavelengths. The H  arms are broader and smoother than the molecular arms. Between R = 4 kpc and R = 12 kpc the brightest CO filaments and the darkest dust lanes define a two-armed spiral pattern that is well described by two logarithmic spirals with a constant pitch angle of 7• -8• . Except for some bridge-like structures between the arms, the interarm regions and the central bulge are free of emission at our sensitivity. The arm-interarm brightness ratio averaged over a length of 15 kpc along the western arms reaches about 20 compared to 4 for H  at an angular resolution of 45 ′′ . In several selected regions we also observed the 12 CO(2-1)-line on a finer grid. Towards the bright CO emission in our survey we find normal ratios of the (2-1)-to-(1-0) line intensities which are consistent with optically thick lines and thermal excitation of CO. We compare the (velocity-integrated) intensity distribution of CO with those of H , FIR at 175 µm and radio continuum, and interpret the CO data in terms of molecular gas column densities. For a constant conversion factor X CO , the molecular fraction of the neutral gas is enhanced in the spiral arms and decreases radially from 0.6 on the inner arms to 0.3 on the arms at R ≃ 10 kpc. We also compare the distributions of H , H 2 and total gas with that of the cold (16 K) dust traced at λ175 µm. The ratios N(H i)/I 175 and (N(H i) + 2N(H 2 ))/I 175 increase by a factor of ∼ 20 between the centre and R ≃ 14 kpc, whereas the ratio 2N(H 2 )/I 175 only increases by a factor of 4. For a constant value of X CO , this means that either the atomic and total gas-to-dust ratios increase by a factor of ∼ 20 or that the dust becomes colder towards larger radii. A strong variation of X CO with radius seems unlikely. The observed gradients affect the cross-correlations between gas and dust. In the radial range R = 8-14 kpc total gas and cold dust are well correlated; molecular gas is better correlated with cold dust than atomic gas. At smaller radii no significant correlations between gas and dust are found. The mass of the molecular gas in M 31 within a radius of 18 kpc is M(H 2 ) = 3.6 × 10 8 M ⊙ at the adopted distance of 780 kpc. This is 12% of the total neutral gas mass within this radius and 7%...