An HST Survey of the Mid-UV Morphology of Nearby Galaxies

     Too little is known about the relation between star formation and the global physical characteristics of galaxies to interpret the morphologies of distant galaxies in terms of their evolutionary status. Distant galaxies are primarily observed by HST in their restframe mid-ultraviolet (2000Å--3000Å). They resemble nearby late-type galaxies, but are they really physically similar classes of objects?

Our team set out to address this question through a Cycle 9 HST/WFPC2 imaging survey of 37 nearby galaxies in the F255W and F300W mid-UV filters (2550Å and 2930Å) and in the red F814W filter (I; 8230Å), and through a Cycle 10 WFPC2 SNAPSHOT survey of 98 nearby galaxies (of which 52 were observed) in the F300W and F814W filters. The combined galaxy sample was selected to include galaxies spanning a wide range in morphological type and inclination, and sufficiently small to fit the WFPC2 field-of-view, and with sufficiently high (predicted) effective UV surface brightnesses to be detectable with WFPC2 in at most one orbit.

The mid-UV spans the gap between ground-based optical and near-IR UBVR(IJ HK) images --available or acquired for our study-- and far-UV images available for a subset of our sample from the Astro/UIT mission and baloon-borne experiments. Our data set is unique, can be applied to a wide range of problems, and has been made available to the public immediately after the observations were taken via the HST Archive.

Our main program goals are to:
1. consistently classify polychromatic structures and photometric properties of galaxies from 0.15--2.2 µm;
2. map the spatial distribution, luminosities, and sizes of star-forming regions responsible for the UV morphology, and relate these to global galaxy properties;
3. provide local benchmark images that may be artificially redshifted to z~1--3 for quantitative comparison with the morphological and photometric properties of high redshift galaxies.

Trough these web-pages, we provide access to the raw and reduced data, the planning and observations, our publications, as well as to press-releases and pretty pictures that are likely to be of more interest to the general public.