Hans Ungerechts

A composite CO survey of the entire milky way

Large-scale CO surveys of the entire Galactic plane and specific nearby clouds have been combined to produce a panorama of the entire Milky Way in molecular clouds at an angular resolution of 1/2°. Covering 10°–20° in latitude at all longitudes and all large, nearby clouds at higher latitude, the composite survey is the only molecular line survey to date with sky coverage and resolution comparable to that of the early 21 cm surveys.

A CO survey of the dark nebulae in Perseus, Taurus, and Auriga

A new SIS receiver with extremely low noise temperature, used on the Columbia 1.2-m telescope has permitted mapping CO rapidly with full sampling. Results are presented of a survey for which the angular resolution of the telescope was reduced to 0.5 deg, allowing the observations for the complete region of 750 square degrees to be finished within four months, while retaining sufficient resolution to see significant substructure. Most positions with emission are in the Taurus-Auriga dark nebulae, a cloud associated with IC 348 and NGC 1333, and a cloud associated with the California nebula (NGC 1499) and NGC 1579, which overlaps the northern Taurus-Auriga nebulae but is separated from them in velocity. Also seen were several small clouds at Galactic latitude -25 deg to -35 deg southwest of the Taurus clouds, and the L1558 and L1551 clouds in the south. 89 references.

A CO Survey of Giant Molecular Clouds near Cassiopeia A and NGC 7538

With the 1.2 m telescope at the Center for Astrophysics we have undertaken a survey of the J \ 1 ) 0 CO line toward the conspicuous complex of giant molecular clouds (GMCs) in the Perseus arm in the region of Cas A and NGC 7538. The survey, at a spectral resolution of 250 kHz (0.65 km s~1), on a uniform grid of points spaced every in latitude and longitude, covers 55 deg2 between l \ 107i and 0i.125 116i. A smaller area of B15 deg2 between l \ 108i and 113i was similarly surveyed in 13CO. In the region covered in both isotopic species we —nd at least seven GMCs with masses on the order of 105 An intensity-weighted radius gives a more meaningful measure of cloud size than the simple geo- M _ . metrical area and is best used to estimate the virial mass. The ratio of total cloud luminosities in CO and 13CO, ranges from 6 to 10, with a mean of 8.5. The distribution of molecular gas is very S 12 /S 13 , similar in CO and 13CO, and the velocity-integrated intensities at each point are closely correlated. In the (l, v)-diagram the Perseus arm is kinematically separated from the local arm by an interarm gap that is nearly free of CO; the contrast in molecular gas surface density between the Perseus arm and the interarm gap is apparently at least 20. Subject headings: Galaxy: structureISM: cloudsISM: individual (NGC 7538) ¨ ISM: molecules