4.3. Late-type Galaxies and Irregulars
The late-type and irregular galaxies imaged are a heterogeneous mixture. The majority of these galaxies show a F300W morphology that is similar to that in F814W. Important differences are seen, however, due to recognizable dust-lanes or pockets blocking out F300W light (e.g., UGC 06697 [Section 3.17]; NGC 5253 [Section 3.27]; UGC 09855 [Section 3.30]; Mrk 66 [Section 3.32]; Arp 299 [Section 3.34]; IC 2184 [Section 3.37]). Dust is visible in pockets, holes or bubbles, perhaps due to supernova-induced outflows or outflows fueled by bright star-forming regions, such as seen in M 82 at HST resolution (de Grijs et al. 2001).
Some late-type galaxies are physically smaller galaxies with what appears to be the beginning of spiral structure (MCG+03 -30 -071 and MCG+06 - 24 - 047 [Section 3.21-3.22], UGC 05028 [Section 3.23], NGC 3860B [Section 3.24], ESO 418 - G008 [Section 3.25], UGC 05626 [Section 3.29]). Others are Magellanic Irregulars (NGC 5253, NGC 1140 and NGC 1510 [Section 3.26-3.28], UGC 09855, NGC 6789, Mrk 66, and UGC 05189 [Section 3.30-3.33]) with various regions of stochastic star-formation. Star-formation "ridges" are commonly seen in the late-type galaxies, as well as hot stars or star-clusters that are particularly conspicuous in the mid-UV (F300W and/or F255W).
A few late-type galaxies would be classified significantly different when observed in the mid-UV than in the F814W passband (MCG+06 - 24 - 047 [Section 3.22], UGC 05626 [Section 3.29], UGC 09855 [Section 3.30]), especially when observed under less than perfect atmospheric seeing conditions. A quantitative discussion of the classification changes as a function of rest-frame wavelength will be given by Odewahn et al. (2002b).