A Hubble Space Telescope Survey of the Mid‐Ultraviolet Morphology of Nearby Galaxies

(Abbreviated) We present an imaging survey of 37 nearby galaxies observedwith HST/WFPC2 in the mid-UV F300W filter and in F814W. 11 galaxies were alsoimaged in F255W. These galaxies were selected to be detectable with WFPC2 inone orbit, and cover a wide range of Hubble types and inclinations. The mid-UVspans the gap between our groundbased optical/NIR images and far-UV imagesavailable from the Astro/UIT missions. Our first qualitative results are: (1) Early-type galaxies show a significant decrease in surface brightnessgoing from the red to the mid-UV, and in some cases the presence of dust lanes.Some galaxies would be classified different when viewed in the mid-UV, somebecome dominated by a blue nuclear feature or point source. (2) Half of the mid-type spiral and star-forming galaxies appear as a latermorphological type in the mid-UV, as Astro/UIT also found in the far-UV. Some-times these differences are dramatic. The mid-UV images show a considerablerange in the scale and surface brightness of individual star-forming regions.Almost all mid-type spirals have their small bulges bi-sected by a dust-lane. (3) Most of the heterogeneous subset of late-type, irregular, peculiar, andmerging galaxies display F300W morphologies that are similar to those seen inF814W, but with differences due to recognizable dust features absorbing thebluer light, and due to UV-bright hot stars, star-clusters, and star-formingridges. In the rest-frame mid-UV, early- to mid-type galaxies are more likely to bemisclassified as later types than vice versa. This morphological K-correctionexplains only part of the excess faint blue galaxies seen in deep HST fields.Comment: 30 pages, LateX (AASTeX5.0), 2 figures and 3 tables included, mid-UV atlas and pan-chromatic atlas provided as 63 JPG figures. Full resolution PS version (~100Mb) available upon request. Accepted for publication in ApJ