GALEX Ultraviolet Imaging of Dwarf Galaxies and Star Formation
  We present ultraviolet integrated and azimuthally-averaged surface
photometric properties of a sample of 44 dIm, BCD, and Sm galaxies measured
from archival NUV and FUV images obtained with GALEX. We compare the UV to
Halpha and V-band properties and convert FUV, Halpha, and V-band luminosities
into star formation rates (SFRs). We also model the star formation history from
colors and compare the integrated SFRs and SFR profiles with radius for these
methods. In most galaxies, the UV photometry extends beyond Halpha in radius,
providing a better measure of the star formation activity in the outer disks.
The Halpha appears to be lacking in the outer disk because of faintness in low
density gas. The FUV and V-band profiles are continuous with radius, although
they sometimes have a kink from a double exponential disk. There is no obvious
difference in star formation properties between the inner and outer disks. No
disk edges have been observed, even to stellar surface densities as low as 0.1
Msun/pc2 and star formation rates as low as 10^{-4} Msun/yr/kpc2. Galaxies with
low HI to luminosity ratios have relatively low FUV compared to V-band emission
in the outer parts, suggesting a cessation of star formation there. Galaxies
with relatively high HI apparently have fluctuating star formation with a Gyr
timescale.
