NOAO >   Observing Info >   Approved Programs >   2009A-0224

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Proposal Information for 2009A-0224


PI: Kate L. Barnes, Indiana University, barneskl@astro.indiana.edu
Address: Astronomy Department, 727 East 3rd St., Bloomington, IN 47405, USA

CoI: Liese van Zee, Indiana University
CoI: Evan D. Skillman, University of Minnesota

Title: Star Formation Activity in the Outer Disk of a Sample of ``Normal'' Spiral Galaxies

Abstract: Recent results from H(alpha) and UV imaging show star formation out to 2-4R_25 in galaxies with extended HI disks. To obtain a census of the current star formation activity in ``normal'' spiral galaxies, we have obtained ultra-deep H(alpha) and UV imaging of a sample of galaxies with typical HI-to-optical size ratios (i.e., ~ 1-1.5). Even in these less extreme systems, we have found ~10-30 star forming complexes beyond R_25. However, in order to extract fully the science potential from these images, we require HII region spectra to obtain measurements of the chemical abundances and extinction. We have measured H(alpha) and UV fluxes and colors of these star forming complexes to quantify the current star formation rates and examine the underlying stellar populations in the outer disk. The outer disk star forming regions show a large range in FUV-NUV colors, and independent metallicity and extinction measurements are needed in order to ensure that these variations are due to the underlying stellar populations. Additionally, these spectra will allow us to significantly increase the sample of galaxies for which abundance gradients in the outer disk have been measured.


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