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 present the results of a high angular resolution, multi-transition analysis of the molecular gas in M 82. The analysis is based on the two lowest transitions of 12 CO and the ground transition of the rare isotopes 13 CO and C 18 O measured with the PdBI, the BIMA array and the IRAM 30 m telescope. In order to address the question of how the intrinsic molecular cloud properties are influenced by massive star formation we have carried out radiative transfer calculations based on the observed CO line ratios. The calculations suggest that the kinetic temperature of the molecular gas is high in regions with strong star formation and drops towards the outer molecular lobes with less ongoing star formation. The location of the highest kinetic temperature is coincident with that of the mid infrared (MIR) peaks which trace emission from hot dust. The hot gas is associated with low H2 densities while the cold gas in the outer molecular lobes has high H2 densities. We find that CO intensities do not trace H2 column densities well. Most of the molecular gas is distributed in a double-lobed distribution which surrounds the starburst. A detailed analysis of the conversion factor from CO intensity to H2 column density shows that XCO depends on the excitation conditions. We find XCO ∼ T −1 kin n(H2) 1/2 , as expected for virialized clouds.
A B S T R A C TWe report the first detection of CO in the bulge of M31. The 12 CO (1±0) and (2±1) lines are both detected in the dust complex D395A/393/384, at 1.3 arcmin (,0.35 kpc) from the centre. From these data and from visual extinction data, we derive a CO luminosity to reddening ratio (and a CO luminosity to H 2 column density ratio) quite similar to that observed in the local Galactic clouds. The (2±1) to (1±0) line intensity ratio points to a CO rotational temperature and a gas kinetic temperature of .10 K. The molecular mass of the complex, inside a 25-arcsec (100 pc) region, is 1X5 Â 10 4 M ( X
Abstract. We have used MERLIN, at 1.4 and 5 GHz, to search for radio supernovae (RSNe) and supernova remnants (SNRs) in the unobscured irregular dwarf galaxy NGC 1569, and in particular in the region of its super star clusters (SSCs) A and B. Throughout NGC 1569 we find some 5 RSNe and SNRs but the SSCs and their immediate surroundings are largely devoid of non-thermal radio sources. Even though many massive stars in the SSCs are expected to have exploded already, when compared with M 82 and its many SSCs the absence of RSNe and SNRs in and near A and B may seem plausible on statistical arguments. The absence of RSNe and SNRs in and near A and B may, however, also be due to a violent and turbulent outflow of stellar winds and supernova ejected material, which does not provide a quiescent environment for the development of SNRs within and near the SSCs.
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