Robert Laurence Dickman

CARBON-MONOXIDE AS AN EXTRAGALACTIC MASS TRACER

The validity of integrated CO emission intensity as a tracer of molecular cloud mass in external galaxies is examined critically. By modeling extragalactic CO emission with an ensemble of independently emitting clouds, each of which obeys the virial theorem, it is demonstrated that, on average, there exists a linear relationship between integral CO intensity and the mass surface density of emitting cloud material lying within a radio telescopes antenna beam. Using molecular cloud parameters typical of the Milky Way, a ratio of mass surface density to integrated CO intensity is found which is within a factor of 2 of those frequently used to interpret extragalactic carbon monoxide observations. 28 references.

MOLECULAR OUTFLOWS ASSOCIATED WITH BRIGHT FAR-INFRARED SOURCES

A systematic search was carried out for high-velocity CO emission associated with bright 100-micron sources from the IRAS Point Source Catalog, in an effort to increase the understanding of the nature and evolutionary status of the objects producing molecular outflows. Eighteen sources with 100-micron flux densities greater than 500 Jy were selected and maps were made in the J = 1-0 (C-12) line around each source. Almost every source observed was found to lie toward, or in the immediate vicinity of, strong CO emission and in most cases close to the maximum of this emission. Thus, all of the far-infrared sources can be associated with molecular clouds. Five of the sources show clear evidence of high-velocity molecular emission and at least three have bipolar morphologies. The newly detected outflow sources are all intrinsically luminous objects, and their outflows energetic. The infrared characteristics of all the sources in the present survey suggest that they are young stellar objects still embedded in their parent molecular clouds. Statistics on the occurrence of outflows from bright far-infrared sources are used to set an upper limit of 400,000 yr for the dispersal time scale of material around young, luminous stellar objects. 31 references.

Molecular Clouds in the Milky Way and External Galaxies

The volume consists of up-to-date reviews and a selection of contributed papers on subjects including the structure and physical properties of molecular clouds, their role in the star formation process, their dust and chemical properties, molecular cloud surveys of the Milky Way, cloud evolution, problems in cloud mass determinations (a panel discussion and review), the CO properties of external galaxies, nuclei of galaxies as revealed by molecular observations, and galactic spiral structure as reflected by molecular cloud distributions. The abstracts of poster papers on these topics presented at the conference are also included. This book is both a valuable reference and a compendium of current knowledge in this field. It should be of special interest to all students and researchers who work on the physics of star formation, the interstellar medium, molecular clouds and galactic structure.

Molecular outflows associated with a flux-limited sample of bright far-infrared sources

Results of a systematic search for high-velocity CO emission from a sample of bright FIR sources from the IRAS Point Source Catalog are presented. This extends the original survey to a complete flux-limited sample. Results of CO mapping toward 22 FIR sources are given, showing that all of the sources are associated with strong CO emission that is peaked close to the FIR sources. Based on their IR colors and positional coincidence with strong CO emission, it is suggested that the sample is composed entirely of luminous, young stellar objects. New detections of molecular outflows were made toward six of the FIR sources. These outflows are relatively energetic, with typical mechanical energies of 10 to the 45th ergs. 30 refs.

Structure and kinematics of dense gas associated with the supernova remnant IC 443

We present the results of systematic, high-resolution J=1→0 CO and HCO + mapping observations of IC 443 carried out with the FCRAO 14 m radio telescope. Five new clumps of perturbed molecular gas have been identified and their relationship to one another clarified. Together with three previously known perturbed regions, the clumps outline a roughly elliptical ring whose major axis is ∼9 pc across

Analysis of (C-12)O and (C-13)O emission in a 3 square degree region of the Galactic plane between L = 23 deg and 25 deg

A 3-sq deg section of the inner Galactic plane centered at l = 24 deg, b = 0 deg in both (C-13)O and CS. The observations were supplemented by preexisting CO data from the Massachusetts-Stony Brook Galactic plane survey. It was possible to identify 47 molecular clouds in the region surveyed. Distances to the clouds were assigned using a size-line width relation which was derived for a set of calibrator clouds at known distances. By combining the CO and (C-13)O data, it was possible to calculate LTE masses for the clouds and to compare them with masses estimated from the virial theorem. Masses estimated from the two methods are tightly correlated, suggesting that the clouds observed in this study are close to virial equilibrium. The masses derived using the two methods are in reasonable agreement. Little CS emission was detected in this section or the Galactic plane; averaged over the region of the survey, the CO/CS integrated intensity ratio is found to be 660 + or - 160, considerably larger than the ratio in the Galactic center. 26 refs.

Star counts and carbon monoxide observations of Maddalena's cloud

We have mapped the inner region of Maddalenas cloud, a massive, cold object in the outer Galaxy, in both 12 CO and 13 CO (J=1-0) using the FCRAO 14 m telescope. The visual extinction has been determined by star counts and is used to investigate the gas and dust properties of the cloud.