Line-strengths in early-type galaxies



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Gorgas García, Francisco Javier and Efstathiou, G. and Aragón Salamanca, A. (1990) Line-strengths in early-type galaxies. Monthly notices of the Royal Astronomical Society, 245 (2). pp. 217-237. ISSN 0035-8711

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We have analysed Mg, Hβ and Fe line-strengths in a sample of elliptical, SO and brightest cluster galaxies. For 15 galaxies, our spectra extend to approximately the half-light 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 strongly with parameters such as total luminosity and rotation, though we find sorne 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 subunits 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. How­ ever, we find that two cD galaxies show Hβ in emission and are also at the centres of the prodigious cooling flows with mass-deposition rates of ≥ 100 M_⨀ 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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© Royal Astronomical Society.
JG would like to thank the lnstitute of Astronomy, Cambridge, and the Department of Astrophysics, Oxford, for their hospitality. He acknowledges support by the Spanish Fondo Nacional para el Desarrollo de la Investi­gación Científica (Project PB85-60). GE would like to thank his observing collaborators; this project would have been impossible without their effects. We thank the British Council for providing travel support.

Uncontrolled Keywords:Astronomy & Astrophysics
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
ID Code:37469
Deposited On:03 May 2016 14:38
Last Modified:10 Dec 2018 15:05

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