Deep UV Imaging of Galaxies in the Fornax Cluster
Authors: Karen O'Neil, G. D. Bothun, Eric P. Smith, & T. P. Stecher
Published:The Astronomical Journal, Vol. 112, pg 431 (1996)
We compare the Astro-1 Ultraviolet Imaging Telescope (UIT)
deep image of the Fornax cluster with deep
optical surveys for purposes of determining the efficacy of vaccuum ultraviolet
imaging in terms of the recovery of very faint and/or diffuse galaxies.
This field covers approximately 1/3 of a square degree and contains
15 galaxies with Bt brighter than 18.0 magnitude. A
1000 second near UV image detected 10 of these galaxies. These 10
detections include 3 luminous ellipticals, 2 bonafide dwarf ellipticals
and 5 galaxies of small angular size that may or may not be members
of the Fornax cluster. IF these optically
faint galaxies are members of the Fornax cluster, then the VUV
imaging did sample an appreciable range in the galaxy luminosity function.
For the dwarf ellipticals, a comparison of
their optical and UV fluxes indicates the UV light is not dominated
by any hot population but rather represents the general UV characteristics
of the underlying stellar population. In particular, we can place an upper
limit of 25 O3-5 stars that are present due to possible low level star
formation. Furthermore, the UV-optical colors of the dEs are significantly
redder than Galactic globular clusters which indicates that these dEs do not
have a significant population of extreme horizontal branch stars.
With the failure
of the near UV camera aboard the Astro-2 mission, the opportuntity
for performing a deeper near UV survey has been lost. We conclude,
however, that such a survey would have good sensitivity to the
detection of optically faint and/or diffuse galaxies and would provide credible
information on the galaxy luminosity function.
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