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P.B. Eskridge (MnSU), V.A. Taylor, R.A. Windhorst, S.C. Odewahn, C.A.T. Chiarenza (ASU), C.J. Conselice (STScI), R. de Grijs (Cambridge), L.D. Matthews (NRAO), R.W. O'Connell (UVA), J.A. Frogel (OSU), J.S. Gallagher (UWi)
We have obtained HST/WFPC2 F300W (NUV) and F814W (I) images of two nearly face-on early-type spiral galaxies (NGC 6753 and NGC 6782) as part of a near-UV imaging survey of nearby galaxies. The NUV images of both galaxies reveal spectacular inner ring structures that are only weakly visible on ground-based optical images. There is no evidence for ongoing star formation in the central parts of either system. Instead, the ongoing star formation in largely confined to regions that can be associated with dynamically important resonances in the spiral disks. Pixel-by-pixel color-magnitude diagrams (pCMDs) reveal multiple plumes of pixels that are strongly spatially correlated with visible structures in the systems. We interpret this as being due to regions of on-going star formation generating high NUV surface brightness, overlayed on an older stellar population that is traced by the generally radially declining I-band surface brightness. The I-band surface brightness profiles are not smooth, but instead show the time-integrated effects of the dynamically driven star formation histories of the disks. We have investigated the well-known red-leak problem of the F300W filter and determined that red-leak is no more than a 10% effect even in the reddest parts of both our targets. The detailed comparison of NUV and red optical images of spirals is an elegant means of tracing out the spatial variation of the relative importance of ongoing and past integrated star formation.
This research is supported by NASA/STScI grants GO-8645.*
The author(s) of this abstract have provided an email address for comments about the abstract: paul.eskridge@mnsu.edu