High-resolution images of the L1551 bipolar outflow: evidence for an expanding, accelerated shell.

Approximately one-half of the L1551 bipolar outflow was mapped in the J = 1-0 transition of 12CO using the FCRAO 14 m telescope. The data were obtained by heavily oversampling over the beam area and then were reconstructed using a maximum entropy algorithm to obtain images of the high-velocity gas with an angular resolution of approximately 20". The outflow exhibits a striking shell-like structure with the lowest velocity out-flowing gas found along the limb of the outflow, and the highest velocity outflowing gas found along the axis of the outflow. A smooth transition is found between low-velocity emission on the periphery and high-velocity gas in the center. Our data can be modeled by molecular material located in a thin expanding shell which is accelerating away from IRS 5.

Galactic evolution: a survey of recent progress.

Current observational knowledge bearing on the evolution of elliptical and disk galaxies is reviewed. Particular emphasis is placed on identifying the factors that appear common to all galaxies of a particular type as opposed to those that seem to depend on environmental conditions. The success of various classes of galactic formation and evolution models used to confront these data is evaluated.