1995A&A...295L..55B

We have used the IRAM 30meter telescope with the MPIfR 7-channel bolometer to map the λ1.3mm continuum emission from the central 4'x3' region of the edge-on spiral NGC 4631. About 6/7 of the flux is due to thermal radiation from cool dust and its distribution has been compared with recent HI and CO maps at similar angular resolution. The remaining 15% is due to the 12CO(2-1) line (∼11%), the ¹³CO(2-1) line (∼1%), and synchrotron and free-free emission. Both the CO and 1.3mm continuum are concentrated in the inner ∼2kpc and have a similar morphology whereas the HI emission is much more extended. To within observational uncertainties, however, the dust emission per gram of interstellarmatter is similar in the atomic and molecular components after making the usual assumptions to convert HI and CO line fluxes to HI and H2 column densities. The fact that the gas mass calculated from the thermal dust emission is equal to or slightly higher than the mass from the HI and CO lines suggests that in NGC 4631 the N(H₂)/I_CO(1-0) ratio is not overestimated.