Authors: N. R. Napolitano; M. Capaccioli; A. J. Romanowsky; N. G. Douglas¹; M. R. Merrifield²; K. Kuijken; M. Arnaboldi³; O. Gerhard⁴; K. C. Freeman⁵

Source: Monthly Notices of the Royal Astronomical Society, Volume 357, Number 2, February 2005 , pp. 691-706(16)

Publisher: Wiley-Blackwell

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: , the logarithmic radial gradient of the mass-to-light ratio. Using halo density profiles from -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 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 , 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 _SF > 1 . This difficulty is eased if dark haloes are not assumed to have the standard CDM profiles, but lower central concentrations.

Keywords: galaxies: evolution; galaxies: fundamental parameters; galaxies: haloes; galaxies: kinematics and dynamics; dark matter

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1365-2966.2005.08683.x

Affiliations: 1: Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, the Netherlands 2: School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD 3: INAF–Astronomical Observatory of Pino Torinese, via Osservatorio 20, I-10025 Pino Torinese, Italy 4: Astronomy department, University of Basel, Venusstrasse, Basel, Switzerland 5: RSAA, Mt. Stromlo Observatory, Weston Creek P.O., ACT 2611, Australia

Publication date: 2005-02-01

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