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

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

2004-11-23

arxiv.org/abs/astro-ph/0411639v1

Astronomy and Astrophysics

Astrophysics

17 pages, 13 figures. Accepted for publication on MNRAS

Scientific paper

10.1111/j.1365-2966.2005.08683.x

Since 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 characterising the halo masses from both observational and theoretical results: \dML, the logarithmic radial gradient of the mass-to-light ratio. Using halo density profiles from LCDM simulations, we derive predictions for this gradient for various galaxy luminosities and star formation efficiencies $\epsilon_{SF}$. As a pilot study, we assemble the available \dML\ data from kinematics in early-type galaxies - representing the first unbiassed study of halo masses in a wide range of early-type galaxy luminosities - and find a correlation between luminosity and \dML, 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 LCDM 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 LCDM profiles, but lower central concentrations.

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