Mass-to-light ratio gradients in early-type galaxy haloes

N. R. Napolitano, M. Capaccioli, A. J. Romanowsky, N. G. Douglas, M. R. Merrifield, K. Kuijken, M. Arnaboldi, O. Gerhard, K. C. Freeman

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Abstract

Owing to the fact that the near future should see a rapidly expanding set of probes of the halo masses of individual early-type galaxies, we introduce a convenient parameter for characterizing the halo masses from both observational and theoretical results: del(l)Y the logarithmic radial gradient of the mass-to-light ratio. Using halo density profiles from Delta-cold dark matter (CDM) simulations, we derive predictions for this gradient for various galaxy luminosities and star formation efficiencies SF. As a pilot study, we assemble the available del(l)Y data from kinematics in early-type galaxies - representing the first unbiased study of halo masses in a wide range of early-type galaxy luminosities - and find a correlation between luminosity and del(l)Y, such that the brightest galaxies appear the most dark-matter dominated. We find that the gradients in most of the brightest galaxies may fit in well with the CDM predictions, but that there is also a population of fainter galaxies whose gradients are so low as to imply an unreasonably high star formation efficiency epsilon(SF) > 1. This difficulty is eased if dark haloes are not assumed to have the standard CDM profiles, but lower central concentrations.

Original languageEnglish
Pages (from-to)691-706
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume357
Issue number2
DOIs
Publication statusPublished - 21-Feb-2005

Keywords

  • galaxies : evolution
  • galaxies : fundamental parameters
  • galaxies : haloes
  • galaxies : kinematics and dynamics
  • dark matter
  • DIGITAL SKY SURVEY
  • DARK-MATTER HALOS
  • GLOBULAR-CLUSTER SYSTEM
  • INFRARED FUNDAMENTAL PLANE
  • DWARF SPHEROIDAL GALAXIES
  • LAMBDA-CDM UNIVERSE
  • ELLIPTIC GALAXIES
  • VELOCITY DISPERSION
  • STELLAR POPULATION
  • SPIRAL GALAXIES

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