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J. L. Higdon, S. J. U. Higdon (Cornell University)
Ring galaxies exhibit large scale and coherent starburst activity triggered by the expanding orbit crowded ring. H-alpha surveys show that massive star formation (MSF) is greatly reduced interior to the starburst rings, making them important for studies of the triggering and suppression of star formation on galaxy wide scales. However, whether or not MSF is completely extinguished in their interiors is still an open question. Deep CFHT H-alpha imaging of the Cartwheel ring galaxy has uncovered a population of L(H-alpha) = 1037.5-1038.5 erg s-1 emission line sources (Ho = 70 km s-1 Mpc-1; AV=0) within its disk, primarily in the wake of the outer ring quadrant experiencing peak starburst activity. Eleven other emission line sources (L(H-alpha) ~ 1038.8 erg s-1) are associated with dust lanes of the inner-ring and the nucleus.
We have combined high resolution U, V, H, & K' images from the VLT with archival WFPC2 B & I maps to measure the optical-NIR spectral energy distributions (SEDs) of the star clusters embedded in the H-alpha sources. This allows us to determine whether they represent low levels of on-going star formation, populations of post-starburst clusters left behind the advancing starburst, or the impacts of dense clouds raining down on the disk from the gas bridge connecting the Cartwheel and ``intruder'' galaxies. We also examine the optical-NIR SEDs of star clusters visible in the broadband images that are not detected in H-alpha.
The author(s) of this abstract have provided an email address for comments about the abstract: jhigdon@astro.cornell.edu