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 : \nabla _ { \ell } \Upsilon , the logarithmic radial gradient of the mass-to-light ratio .
Using halo density profiles from \Lambda CDM 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 \nabla _ { \ell } \Upsilon 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 \nabla _ { \ell } \Upsilon , 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 \Lambda 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 \Lambda CDM profiles , but lower central concentrations .