Mass-to-light ratio gradients in early-type galaxy haloes |
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| Authors: | 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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| Institution: | Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, the Netherlands;INAF–Astronomical Observatory of Capodimonte, via Moiariello 16, I-80131 Naples, Italy;Department of Physical Sciences, University "Federico II", Naples, Italy;Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción, Chile;School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD;Leiden Observatory, Niels Bohrweg 2, NL-2333 CA Leiden, the Netherlands;INAF–Astronomical Observatory of Pino Torinese, via Osservatorio 20, I-10025 Pino Torinese, Italy;Astronomy department, University of Basel, Venusstrasse, Basel, Switzerland;RSAA, Mt. Stromlo Observatory, Weston Creek P.O., ACT 2611, Australia |
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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: ??? , the logarithmic radial gradient of the mass-to-light ratio. Using halo density profiles from Λ-cold dark matter (CDM) simulations, we derive predictions for this gradient for various galaxy luminosities and star formation efficiencies εSF . 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 ΛCDM 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 εSF > 1 . This difficulty is eased if dark haloes are not assumed to have the standard ΛCDM profiles, but lower central concentrations. |
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| Keywords: | galaxies: evolution galaxies: fundamental parameters galaxies: haloes galaxies: kinematics and dynamics dark matter |
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