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For refcode 1998ApJ...504L..17V:
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Copyright by American Astronomical Society. Reproduced by permission
1998ApJ...504L..17V Luminosity Evolution of Early-Type Galaxies to z = 0.83: Constraints on Formation Epoch and {OMEGA} PIETER G. VAN DOKKUM, MARIJN FRANX, DANIEL D. KELSON, AND GARTH D. ILLINGWORTH Received 1998 May 28; accepted 1998 July 1; published 1998 July 23 ABSTRACT We present deep Keck telescope spectroscopy of eight galaxies in the luminous X-ray cluster MS 1054-03 at z=0.83. The data are combined with imaging observations from the Hubble Space Telescope (HST). The spectroscopic data are used to measure the internal kinematics of the galaxies, and the HST data are used to measure their structural parameters. Six galaxies have early-type spectra, and two have "E+A" spectra. The galaxies with early-type spectra define a tight fundamental plane (FP) relation. The evolution of the mass-to-light ratio is derived from the FP. The M/L ratio evolves as {DELTA}log M/L_B_ is proportional to -0.40z ({OMEGA}_m =0.3, {OMEGA}_{LAMBDA}_ = 0). The observed evolution of the M/L ratio provides a combined constraint on the formation redshift of the stars, the initial mass function (IMF), and cosmological parameters. For a Salpeter IMF (x = 2.35), we find that z_form_ > 2.8 and {OMEGA}_m_ < 0.86 with 95% confidence. The constraint on the formation redshift is weaker if {OMEGA}_{LAMBDA} > 0: z_form_ > 1.7 if {OMEGA}_m_ = 0.3 and {OMEGA}_{LAMBDA}_ = 0.7. At present, the limiting factor in constraining z_form_ and {OMEGA} from the observed luminosity evolution of early-type galaxies is the poor understanding of the IMF. We find that if {OMEGA}_m_ = 1, the IMF must be significantly steeper than the Salpeter IMF (x > 2.6). Subject headings: galaxies: clusters: individual (MS 1054-03)-galaxies: elliptical and lenticular, cD-galaxies: evolution-galaxies: structure
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