Age-dating luminous red galaxies observed with the Southern African Large Telescope

A. L. Ratsimbazafy, S. I. Loubser, S. M. Crawford, C. M. Cress, B. A. Bassett, R. C. Nichol, P. Väisänen

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We measure a value for the cosmic expansion of H(z)=89±23(stat) ± 44(syst) km s−1 Mpc−1 at a redshift of z≃0.47 based on the differential age technique. This technique, also known as cosmic chronometers, uses the age difference between two redshifts for a passively evolving population of galaxies to calculate the expansion rate of the Universe. Our measurement is based on analysis of high quality spectra of Luminous Red Galaxies (LRGs) obtained with the Southern African Large Telescope (SALT) in two narrow redshift ranges of z≃0.40 and z≃0.55 as part of an initial pilot study. Ages were estimated by fitting single stellar population models to the observed spectra. This measurement presents one of the best estimates of H(z) via this method at z∼0.5 to date.
Original languageEnglish
Pages (from-to)3239-3254
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 6 Feb 2017


  • galaxies: elliptical and lenticular, cD
  • galaxies: evolution
  • cosmological parameters
  • cosmology: observations


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