Program: GN-2009A-Q-101
Title: | Star Formation Activity in the Outer Disk of a Sample of ``Normal'' Spiral Galaxies |
PI: | Kate L Barnes |
Co-I(s): | Liese Van Zee, Evan D Skillman |
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., $\sim$ 1-1.5).
Even in these less extreme systems, we have found $\sim$10-30 star
forming complexes beyond R$_{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.