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. (5426 kb) (42 kb)