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For refcode 1990MNRAS.245..217G:
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Copyright by Royal Astronomical Society. 1990MNRAS.245..217G Line-strengths in early-type galaxies J. Gorgas, G. Efstathiou and A. Aragon Salamanca Departamento de Astrogica. Facultad de Fisicas, Universidad Complutense, 28040 Madrid, Spain Department of Astrophysics, Keble Road, Oxford OX1 3RH Department of Physics, South Road, Durham DH1 3LE Accepted 1990 February 13. Received 1990 January 29; in original form 1989 June 29 SUMMARY We have analysed Mg, H{beta} and Fe line-strengths in a sample of elliptical, S0 and brightest cluster galaxies. For 15 galaxies, our spectra extend to approximately the half-bright radius (r_e_), and we are able to measure radial line-strength gradients. The metallic line-strength gradients vary markedly from object to object, and do not correlate find some evidence that gradients in the Mg_2_ index correlate with central velocity dispersion and central line-strength. The highly variable line- strength gradients in early-type galaxies shows that they have experienced different star formation histories. We suggest that this may be explained if they formed by the mergers of submits in which star formation had proceeded to varying degrees of completion. We find that the line-strengths at r~r_e_ in elliptical galaxies are slightly larger than those of metal- rich galactic globulars, suggesting that typical elliptical galaxies have roughly solar abundance at r~r_e_ and therefore that most ellipticals have relatively weak abundance gradients. The relative line-strengths in the outer parts of ellipticals differ from those in the nuclei of low- luminosity ellipticals, indicating that these stellar populations do not represent a simple one-parameter family governed by mean metal abundance. We find no significant differences in the central Mg and Fe line-strengths of the brightest cluster galaxies and normal ellipticals with the same central velocity dispersion. However, we find that two cD galaxies show H{beta} in emission and are also at the centres of the prodigious cooling flows with mass-deposition rates of >~100 M_sun_ yr^-1^. Galaxies with cooling flows have identical Mg and Fe line-strengths to galaxies without cooling flows. We show that this implies that only a small fraction of the total luminosity of cooling flow galaxies could come from ongoing star formation with a normal stellar initial mass function.
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