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

Abstract

The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward of rest-frame 2500 A. It is a ubiquitous phenomenon in nearby giant elliptical galaxies, 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 A, providing a measurement of the UV upturn at a lookback time of approximately 4 Gyr. Surprisingly, the four elliptical galaxies observed show a range of UV upturn strength that is similar to that seen in nearby elliptical galaxies, with an equivalent 1550-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 (z_f >= 4).

4 pages, Latex. 1 figure. To appear in ApJL. Uses emulateapj.sty and apjfonts.sty. Revision includes minor ApJ edits & fixes typos

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• Far-Ultraviolet Emission from Elliptical Galaxies at z=0.33
• Extremely Red Objects in the Field of QSO 1213-0017: A Galaxy Concentration at z=1.31
• Evolution of the UV Excess in Early-Type Galaxies
• The Look-back Time Evolution of Far-UV Flux from Elliptical Galaxies: The Fornax Cluster and Abell 2670
• Probing the Interstellar Medium in Early type galaxies with ISO observations
• Modelling the UV spectrum of SDSS-III/BOSS galaxies: hints towards the detection of the UV upturn at high-z
• The UV Upturn: From M32 to Distant Clusters
• The hot stars in orbit around the M31 central supermassive black hole: are they young or old?
• The rise and fall of the UV upturn: $z=0.3,0.55$ and $0.7$
• Evolution of the UV upturn in cluster galaxies: Abell 1689
• UV Imaging of the Galaxy Cluster CL0939+4713 (Abell 851) at z=0.41
• Environmental Effects on the UV Upturn in Local Clusters of Galaxies
• Evolution of the Ultraviolet Upturn at $0.3<z<1$: exploring helium rich stellar populations
• The Ultraviolet Upturn in field Luminous Red Galaxies at $0.3<z<0.7$
• Two categories of UV-upturn galaxies revealed by semi-analytic models