Central mass-to-light ratios and dark matter fractions in early-type galaxies

Abstract

Dynamical studies of local elliptical galaxies and the Fundamental Plane point to a strong dependence of the total mass-to-light ratio (M/L) on luminosity with a relation of the form M/L alpha L-gamma. The 'tilt' gamma may be caused by various factors, including stellar population properties (metallicity, age and star formation history), initial mass function, rotational support, luminosity profile non-homology and dark matter (DM)\ud fraction. We evaluate the impact of all these factors using a large\ud uniform data set of local early-type galaxies from Prugniel & Simien. We take particular care in estimating the stellar masses, using a general star formation history, and comparing different population synthesis models. We find that the stellar M/L contributes little to the tilt. We estimate the total M/L using simple Jeans dynamical models, and find that adopting accurate luminosity profiles is important but does not remove the\ud need for an additional tilt component, which we ascribe to DM. We survey trends of the DM fraction within one effective radius, finding it to be roughly constant for galaxies fainter than M-B similar to -20.5, and increasing with luminosity for the brighter galaxies; we detect no significant differences between S0s and fast- and slow-rotating ellipticals. We construct simplified cosmological mass models and find general consistency, where the DM transition point is caused by a change in the relation between luminosity and effective radius. A more refined\ud model with varying galaxy star formation efficiency suggests a transition from total mass profiles (including DM) of faint galaxies distributed similarly to the light to near-isothermal profiles for the bright galaxies. These conclusions are sensitive to various systematic uncertainties which we investigate in detail, but are consistent with the results of dynamical studies at larger radii

SUPERMASSIVE BLACK HOLES AND THEIR HOST SPHEROIDS. II. THE RED AND BLUE SEQUENCE IN THE MBH–M*,SPH DIAGRAM

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Towards a census of supercompact massive galaxies in the Kilo Degree Survey

“…Total magnitudes derived from the Sérsic fitting, mS, are used to correct the outcomes of Le Phare for missing flux. The single burst assumption is suitable to describe the old stellar populations in the compact galaxies we are interested in (Thomas et al 2005;Tortora et al 2009). The estimated photometric ages are used to check if galaxies are compatible with being relic remnants of systems formed at z ∼ 2.…”

Dark matter halos around isolated ellipticals

“…Do ellipticals follow a similar scenario (see Bertola et al 1993;Salucci & Persic 1997;Tortora et al 2009)? The answer would be of crucial importance for understanding how galaxies form and perhaps even for the nature of the dark matter (DM) itself.…”