Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....107....8f&link_type=abstract
The Astronomical Journal, vol. 107, no. 1, p. 8-23
Astronomy and Astrophysics
Astronomy
20
Balmer Series, Emission Spectra, Galactic Clusters, Galactic Evolution, Sky Surveys (Astronomy), Star Formation, X Ray Sources, Absorption Spectra, Astronomical Photometry, Spectrophotometry, Spectrum Analysis, Stellar Luminosity
Scientific paper
We present a photometric and spectroscopic survey of two clusters of galaxies at z = 0.42. These are members of a sample of five distant, high x-ray luminosity clusters of galaxies, which have been selected from the Einstein Medium Sensitivity Survey Catalog (EMSS). Our objective is to compare the galaxy population in these x-ray selected clusters to the populations in optically selected clusters, which show strong evolution. We have obtained R and I photometry complete to R approximately 22.3 in a 5.7 min x 6.5 min field centered on each cluster. In addition, we have obtained the spectra of 69 galaxies in the direction of the two clusters; 53 of these are cluster members. The x-ray luminosities of Cl 0303+1658 and Cl 0302+1717 (0.2-4.5 keV) are approximately 5 x 1044 and approximately 4 x 1044 ergs, and their velocity dispersions are 921 +192/-123 and 821 +137/-94 km/s, respectively. The evolution of the galaxy population observed in optically selected clusters at z approximately 0.4 (as compared with clusters at the present epoch) is also found in these x-ray selected clusters. This confirms the results that we presented in a previous paper for Cl 1358+6245 at z = 0.33. In both optically and x-ray selected clusters at z approximately 0.4, 20-30% of the galaxies have spectra with strong Balmer absorption lines or emission lines, consistent with recent star formation activity. We identify one possible difference between the optically and x-ray selected clusters; galaxies with very strong Balmer absorption lines, EW between Hdelta + Hgamma but greater than 8 A, are so far absent in our x-ray selected sample, yet they constitute approximately 25% of the spectroscopically active population in Dressler and Gunn's optically selected sample.
Bautz Marshall W.
Fabricant Daniel G.
McClintock Jeffrey E.
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