SPIDER - VII. The Central Dark Matter Content of Bright Early-Type Galaxies: Benchmark Correlations with Mass, Structural Parameters and Environment

Details SPIDER - VII. The Central Dark Matter Content of Bright Early-Type Galaxies: Benchmark Correlations with Mass, Structural Parameters and Environment SPIDER - VII. The Central Dark Matter Content of Bright Early-Type Galaxies: Benchmark Correlations with Mass, Structural Parameters and Environment

2012-01-13

arxiv.org/abs/1201.2945v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

18 pages, 11 figures, 2 tables, submitted to MNRAS

Scientific paper

We analyze the central dark-matter (DM) content of $\sim 4,500$ massive ($M_\star \gsim 10^{10} \, M_\odot$), low-redshift ($z<0.1$), early-type galaxies (ETGs), with high-quality $ugrizYJHK$ photometry and optical spectroscopy from SDSS and UKIDSS. We estimate the "central" fraction of DM within the $K$-band effective radius, \Re. The main results of the present work are the following: (1) DM fractions increase systematically with both structural parameters (i.e. \Re, and S\'ersic index, $n$) and mass proxies (central velocity dispersion, stellar and dynamical mass), as in previous studies, and decrease with central stellar density. 2) All correlations involving DM fractions are caused by two fundamental ones with galaxy effective radius and central velocity dispersion. These correlations are independent of each other, so that ETGs populate a central-DM plane (DMP), i.e. a correlation among fraction of total-to-stellar mass, effective radius, and velocity dispersion, whose scatter along the total-to-stellar mass axis amounts to $\sim 0.15$ dex. (3) In general, a Chabrier IMF is favoured with respect to a bottom-heavier Salpeter IMF, as the latter produces negative (i.e. unphysical) DM fractions for more than 50% of the galaxies in our sample. For a Chabrier IMF, the DM estimates agree with $\Lambda$CDM toy-galaxy models based on contracted DM-halo density profiles. We also find agreement with predictions from hydrodynamical simulations. (4) The central DM content of ETGs does not depend significantly on the environment where galaxies reside, with group and field ETGs having similar DM trends.

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