UV Observations of Clusters of Galaxies with UIT

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Session 7 -- Clusters of Galaxies/Binary Galaxies
Display presentation, Monday, June 12, 1995, 9:20am - 6:30pm

[7.03] UV Observations of Clusters of Galaxies with UIT

E.P.Smith (LASP - NASA/GSFC), R.C.Bohlin (STScI), R.W.O'Connell (UVa), M.S.Roberts (NOAO), A.M.Smith, T.P.Stecher (LASP - NASA/GSFC)

We present ASTRO-1 Ultraviolet Imaging Telescope (UIT) images of 5 galaxy cluster fields and investigate the ultraviolet (UV), 1250\AA\/ $< \lambda <$ 3300\AA\/, properties of the member galaxies. UV imaging is of critical importance to studies of galaxy formation and evolution. Because the UV part of the spectrum isolates the hottest stellar sources, imaging in this band is well suited to study young or star forming regions in galaxies. Similarly, hot, evolved stellar systems are best studied in the ultraviolet. This ability to isolate both the earliest and highly evolved stages of stellar evolution combined with the extremely low UV sky brightness make the UV imaging an important tool for studying galaxies. UV studies of clusters of galaxies have additional significance. Somewhere between the current epoch and redshifts of $\sim\!$0.5 galaxies that make up clusters have undergone dramatic changes. Nearby clusters are dominated by ellipticals whereas those at higher redshifts are composed of much larger fractions of blue galaxies (Butcher \& Oemler 1978, 1984). This suggests that cluster galaxies have evolved rapidly in the last 5 Gyr. Optical images of galaxies at the upper reaches of this redshift range begin to sample the rest--frame UV light. To interpret higher redshift data we must understand low redshift UV properties of cluster galaxies. To address these concerns UIT imaged several nearby clusters of galaxies. We compare our photometric measurements with those from earlier UV studies of galaxies as well as theoretical models of galaxy evolution and derive estimates for the star formation rates of several cluster spirals. We also present preliminary data from clusters of galaxies observed with UIT during the recently completed ASTRO-2 mission.

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