One millimeter continuum observations of extragalactic thermal sources

A composite bolometer detector system operating at 0.370K has been developed for making 1 mm continuum observations using the 5 m Hale telescope on Mount Palomar. The cryostat employs adsorption pumping of liquid 3He to attain this low temperature. The 3He detector system has been used to make 1 mm continuum observations of extragalactic thermal sources. Eight spiral galaxies, NGC 1068, and M 82 were observed. Of this sample, M 82, NGC 253, NGC 4631, and NGC 6946 were detected with a statistical significance of better than 2 sigma. The 3 sigma upper limits of the other galaxies were approximately 1 Jy. For the galaxies in the sample that have been detected at far infrared wavelengths (M 82, NGC 253, NGC 6946, NGC 1068, and IC 342), the 1 mm points are found to lie on a modified black body curve B = B(ν,T)νP. The 1 mm results indicate that p approx. = 1.5 for NGC 253, M 82, and NGC 6946, while for NGC 1068 p greater than or equal to 2.0. The color temperatures derived from the far infrared observations lie in the 30 to 400K range. Similar parameters result from observations of molecular clouds in our galaxy. Therefore, the observations are consistent with the 1 mm emission from the galaxies originating in a molecular cloud environment. This would imply that there is not a great deal of 10 to 200K interstellar dust in these galaxies. There seems to be no correlation between the 1 mm flux and the total HI emission from the galaxies. There is perhaps a correlation between the level of synchrotron emission and the 1 mm flux from the galaxies. The 1 mm flux from three points along the galactic plane of M82 was measured. Only emission from the nucleus was detected, indicating that the dust distribution is strongly peaked at the location of the nucleus. This sharp peak is also seen in CO