AN HSTACS/WFC H IMAGING SURVEY OF NEARBY GALAXIES

Abstract Previous studies of nearby galaxies show large discrepancies between different star formation (SF) indicators on large ( ¡ ¢ 100 pc, or even global) scales: the strikingly complex interplay of young stars, dust and ionized gas are the primary cause of this variance. The few galaxies in the HST Archive with both H £ and mid-UV images show this complex geometry to extend down to pc scales. To provide a benchmark for understanding SF processes at spatial resolutions that are unattainable from the ground in normal and star-bursting, barred and non-barred galaxies, I am conducting an H £ SNAPshot survey with ACS/WFC of ¡ 24 galaxies of all Hubble types, that are nearby but beyond the Local Group and that were previously imaged with HST in the mid-UV and red. These data can be used to address a wide range of astrophysical problems, but the immediate goals are to: (1) spatially resolve the dust clouds and filaments which strongly affect mid-UV and H £ derived SF rates, (2) test how the largescale correlation between H £ and mid-UV flux breaks down on pc scales, and (3) model the propagation of star formation by comparing the SF over time scales of ¡ 100 Myr (via mid-UV) and ¡ 5 Myr (via H £). This will (4) significantly improve our insight into, and calibration of SF in UV-bright galaxies at high ¤, and into the cosmic SF history