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Far-Ultraviolet Emission from Elliptical Galaxies at z=0.33 | Thomas M. Brown
; Henry C. Ferguson
; Ed Smith
; Charles W. Bowers
; Randy A. Kimble
; Alvio Renzini
; R. Michael Rich
; | Date: |
17 Dec 2002 | Subject: | astro-ph | Affiliation: | STScI), Charles W. Bowers, Randy A. Kimble (GSFC), Alvio Renzini (ESO), and R. Michael Rich (UCLA | Abstract: | We present far-ultraviolet (far-UV) images of the rich galaxy cluster ZwCl1358.1+6245, taken with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope (HST). When combined with archival HST observations, our data provide a measurement of the UV-to-optical flux ratio in 8 early-type galaxies at z=0.33. Because the UV flux originates in a population of evolved, hot, horizontal branch (HB) stars, this ratio is potentially one of the most sensitive tracers of age in old populations -- it is expected to fade rapidly with lookback time. We find that the UV emission in these galaxies, at a lookback time of 3.9 Gyr, is significantly weaker than it is in the current epoch, yet similar to that in galaxies at a lookback time of 5.6 Gyr. Taken at face value, these measurements imply different formation epochs for the massive ellipticals in these clusters, but an alternative explanation is a "floor" in the UV emission due to a dispersion in the parameters that govern HB morphology. | Source: | arXiv, astro-ph/0301364 | Services: | Forum | Review | PDF | Favorites |
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