AAS Meeting #193 - Austin, Texas, January 1999
Session 9. Elliptical Galaxies
Display, Wednesday, January 6, 1999, 9:20am-6:30pm, Exhibit Hall 1

[Previous] | [Session 9] | [Next]

[9.07] Measurements of Far-UV Emission from Elliptical Galaxies at z=0.375

T. M. Brown (NASA/GSFC), H. C. Ferguson (STScI), J.-M. Deharveng (MarsLab), R. I. Jedrzejewski (STScI)

The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward of rest-frame 2500~Å. It is a ubiquitous phenomenon in nearby giant ellipticals, and is thought to arise primarily from low-mass evolved stars on the extreme horizontal branch and beyond. Models suggest that the UV upturn is a very strong function of age for these old stellar populations, increasing as the galaxy gets older. In some models the change in UV/optical flux ratio is a factor of 25 over timescales of less than 3 Gyr.

To test the predictions for rapid evolution of the UV upturn, we have observed a sample of normal elliptical galaxies in the z=0.375 cluster Abell~370 with the Faint Object Camera aboard the Hubble Space Telescope. A combination of two long-pass filters was used to isolate wavelengths shortward of rest-frame 2700~Å, providing a measurement of the UV upturn at a lookback time of approximately 4~Gyr. Surprisingly, the four ellipticals observed show a range of UV upturn strength that is similar to that seen in nearby ellipticals, with an equivalent m1550-V color ranging from 2.9--3.4 mag. Our result is inconsistent with some models for the UV upturn; other models are consistent only for a high redshift of formation (zf \ge 4).

If you would like more information about this abstract, please follow the link to http://xxx.lanl.gov/abs/astro-ph/9810216. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract: tbrown@pulsar.gsfc.nasa.gov

[Previous] | [Session 9] | [Next]