Y.-L. Huang

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 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.

Molecular clouds and supernova remnants in the outer galaxy

The study of extragalactic supernova (SNs) suggests that Type II SNs, not Type I, tend to occur near extreme optical Population I objects, but the detection of these objects in the Galaxy is limited by heavy local obscuration. A CO survey has been conducted toward every confirmed outer Galaxy SNR from l = 70 to 210 deg, for a total of 26, and it is found that roughly half of them, within uncertainties of distance estimates, revealed spatial coincidences with large molecular cloud complexes. Most of the cloud complexes in these coincidences probably are the birthplaces of the progenitors of the corresponding Type II SNRs, because it is statistically improbable that the coincidences result from change superposition. 118 references.

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

The molecular content of interacting and isolated galaxies The effect of environment on the efficiency of star formation

Molecular gas observations of merging/interacting and isolated galaxies are presented in order to study the relationship between environment and the efficiency of star formation. The two galaxy samples differ primarily in their IR properties and are quite similar in their molecular gas contents. The ratios of IR luminosity to H2 mass have a mean value of 78 and 12 solar luminosity/solar mass for interacting and isolated galaxies, respectively. The highest star formation efficiencies (SFEs) appear to occur in the merging and interacting pairs. The SFE in merging/interacting galaxies is greater than that found in the spiral arms of M51 and may be roughly proportional to the rate of cloud-cloud collisions in the interacting systems. 27 references.

CO pedestal features from IRAS sources in dark clouds

A sample of IRAS sources within the boundaries of dark clouds has been surveyed for broad-winged CO emission. Five of the 19 selected objects have broad-winged CO emission characteristic of molecular outflow. These objects are similar in characteristics to outflow sources associated with pre-main-sequence stars. These results add to the growing body of evidence that molecular outflows accompany the pre-main-sequence evolution of low-mass stars. 10 references.

On the local environment of extragalactic supernovae

Since Type II supernovae (SNs II) have never been observed in elliptical galaxies and tend to occur in the arms of spirals, it is generally believed that they are associated with the classic Population I tracers of the arms: giant H II regions and OB associations. However, this association has never been directly demonstrated with an adequate number of supernovae. An attempt was made to search for evidence of massive star formation in the immediate vicinity of 56 SNs II. High-quality optical galaxy photos have been located for 29 out of the 56 SNs II. Of these 29 supernovae, 25 lie toward or very near nebulous knots, the plausible signature of star-forming complexes. It is argued that such a large number of apparent coincidences cannot result from chance superposition. These coincidences provide the most direct evidence to date to support the hypothesis that most, if not all, SNs II arise from massive progenitors. The local environment of Type I supernovae in spiral and irregular galaxies is also discussed.