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For refcode 1995AJ....109.1433D:
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1995AJ....109.1433D STELLAR POPULATION GRADIENTS IN BRIGHT CLUSTER GALAXIES AT z = 0.2 T. J. DAVIDGE Gemini Canada Project Office, Dominion Astrophysical Observatory, 5071 West Saanich Road, Victoria, British Columbia, V8X4M6, Canada and Department of Geophysics & Astronomy, University of British Columbia, Vancouver, British Columbia, V6T1Z4, Canada Electronic mail: davidge@dao.nrc.ca M. GRINDER Co-op Program, Department of Physics & Astronomy, University of Victoria, Victoria, British Columbia V8W 3P7, Canada Electronic mail: mgrinder@uvphys.phys.uvicyca Received 1994 November 13; revised 1995 January 11 ABSTRACT Slit spectra, covering the rest frame near-ultraviolet and blue wavelength regions, are combined with moderately deep g and R images to investigate radial population gradients in the brightest components of six z = 0.2 galaxy clusters selected according to x-ray brightness. We conclude that the brightest members of the EMSS 0440+02, EMSS 0906+11, and EMSS 1231+15 clusters have global stellar contents similar to nearby elliptical galaxies, although all three galaxies studied in EMSS 0440 contain a central blue component, suggesting that a young or intermediate-age population is also present. Our ability to investigate the stellar content of the brightest cluster galaxies (BCGs) in the clusters EMSS 0839+29, EMSS 1455+22, and Abell 2390 is complicated by ionized gas, which is detected over large portions of all three systems. Radial color variations are detected in the majority of galaxies and, for those systems not showing extended [O II] emission, there is a tendency for the 4000 A break to weaken with increasing radius, such that {DELTA}D4000/{DELTA}log(r), where D4000 measures the strength of the 4000 A break in magnitudes, falls near the upper range of what is seen among nearby ellipticals. However, there is no correlation between local D4000 values and g - r), suggesting that these quantities are sensitive to different parameters. There is a slight tendency for the steepest spectroscopic gradients to occur in the BCGs. We estimate the metallicity sensitivity of the 4000 A break using a combination of observational and theoretical data, and find that {DELTA}D4000/{DELTA}[Fe/H]~0.4-0.8 in the super metal-rich regime. The metallicity gradients derived for the BCGs from this calibration are relatively steep, and are in qualitative agreement with predictions for galaxies which experience a single monolithic dissipative collapse. Line gradients measured with respect to g surface brightness, as opposed to radius, show excellent galaxy-to- galaxy consistency, and are in good agreement with what has been measured in Coma cluster galaxies, suggesting that common physical processes controlled the early phases of star formation and chemical enrichment in these systems. The presence of significant stellar population gradients in the BCGs suggests that the material from which they formed experienced dissipation during the collapse phases, and it seems likely that these galaxies could not have formed solely from the merging of gas-poor galaxies.
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