Open AccessMass‐to‐light ratio gradients in early‐type galaxy haloes
Author(s) -
Napolitano N. R.,
Capaccioli M.,
Romanowsky A. J.,
Douglas N. G.,
Merrifield M. R.,
Kuijken K.,
Arnaboldi M.,
Gerhard O.,
Freeman K. C.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.08683.x
Subject(s) - physics , astrophysics , halo , galaxy , dark matter halo , dark matter , astronomy , galaxy rotation curve , galaxy formation and evolution , luminosity
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: ∇ ℓ ϒ , 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 ε SF . As a pilot study, we assemble the available ∇ ℓ ϒ 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 ∇ ℓ ϒ , 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 ε SF > 1 . This difficulty is eased if dark haloes are not assumed to have the standard ΛCDM profiles, but lower central concentrations.