The ATLAS^{3D} project  XV. Benchmark for earlytype galaxies scaling relations from 260 dynamical models: masstolight ratio, dark matter, Fundamental Plane and Mass Plane
Abstract
We study the volumelimited and nearly massselected (stellar mass M_{stars} ≳ 6 × 10^{9} M_{☉}) ATLAS^{3D} sample of 260 earlytype galaxies (ETGs, ellipticals Es and lenticulars S0s). We construct detailed axisymmetric dynamical models (Jeans Anisotropic MGE), which allow for orbital anisotropy, include a dark matter halo and reproduce in detail both the galaxy images and the highquality integralfield stellar kinematics out to about 1R_{e}, the projected halflight radius. We derive accurate total masstolight ratios (M/L)_{e} and dark matter fractions f_{DM}, within a sphere of radius r={R_e} centred on the galaxies. We also measure the stellar (M/L)_{stars} and derive a median dark matter fraction f_{DM} = 13 per cent in our sample. We infer masses M_{JAM} ≡ L × (M/L)_{e} ≈ 2 × M_{1/2}, where M_{1/2} is the total mass within a sphere enclosing half of the galaxy light. We find that the thin twodimensional subset spanned by galaxies in the (M_JAM,σ _e,R_e^maj) coordinates system, which we call the Mass Plane (MP) has an observed rms scatter of 19 per cent, which implies an intrinsic one of 11 per cent. Here, R_e^maj is the major axis of an isophote enclosing half of the observed galaxy light, while σ_{e} is measured within that isophote. The MP satisfies the scalar virial relation M_JAM∝ σ _e^2 R_e^maj within our tight errors. This show that the larger scatter in the Fundamental Plane (FP) (L, σ_{e}, R_{e}) is due to stellar population effects [including trends in the stellar initial mass function (IMF)]. It confirms that the FP deviation from the virial exponents is due to a genuine (M/L)_{e} variation. However, the details of how both R_{e} and σ_{e} are determined are critical in defining the precise deviation from the virial exponents. The main uncertainty in masses or M/L estimates using the scalar virial relation is in the measurement of R_{e}. This problem is already relevant for nearby galaxies and may cause significant biases in virial mass and size determinations at high redshift. Dynamical models can eliminate these problems. We revisit the (M/L)_{e}σ_{e} relation, which describes most of the deviations between the MP and the FP. The bestfitting relation is (M/L)_e∝ σ _e^{0.72} (r band). It provides an upper limit to any systematic increase of the IMF mass normalization with σ_{e}. The correlation is more shallow and has smaller scatter for slow rotating systems or for galaxies in Virgo. For the latter, when using the best distance estimates, we observe a scatter in (M/L)_{e} of 11 per cent, and infer an intrinsic one of 8 per cent. We perform an accurate empirical study of the link between σ_{e} and the galaxies circular velocity V_{circ} within 1R_{e} (where stars dominate) and find the relation max (V_{circ}) ≈ 1.76 × σ_{e}, which has an observed scatter of 7 per cent. The accurate parameters described in this paper are used in the companion Paper XX (Cappellari et al.) of this series to explore the variation of global galaxy properties, including the IMF, on the projections of the MP.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 July 2013
 DOI:
 10.1093/mnras/stt562
 arXiv:
 arXiv:1208.3522
 Bibcode:
 2013MNRAS.432.1709C
 Keywords:

 galaxies: elliptical and lenticular;
 cD;
 galaxies: evolution;
 galaxies: formation;
 galaxies: kinematics and dynamics;
 galaxies: structure;
 Astrophysics  Cosmology and Extragalactic Astrophysics
 EPrint:
 35 pages, 18 figures, LaTeX. Accepted for publication in MNRAS. Includes a new data table and figures of all dynamical models. More information about our Atlas3D project is available at http://purl.org/atlas3d