The ATLAS3D project – XV. Benchmark for early-type galaxies scaling relations from 260 dynamical models: mass-to-light ratio, dark matter, Fundamental Plane and Mass Plane

Abstract

We study the volume-limited and nearly mass selected (stellar mass M stars > ∼ 6 × 10 9 M ) ATLAS 3D sample of 260 early-type galaxies (ETGs, ellipticals Es and lenticulars S0s). We construct detailed axisymmetric dynamical models (JAM), which allow for orbital anisotropy, include a dark matter halo, and reproduce in detail both the galaxy images and the highquality integral-field stellar kinematics out to about 1R e , the projected half-light radius. We derive accurate total mass-to-light 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% 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 two-dimensional subset spanned by galaxies in the (M JAM , σ e , R maj e ) coordinates system, which we call the Mass Plane (MP) has an observed rms scatter of 19%, which implies an intrinsic one of 11%. Here R maj e 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 2 e R maj e 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 best-fitting relation is (M/L) e ∝ σ 0.72 e (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%, and infer an intrinsic one of 8%. 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%. The accurate parameters described in this paper are used in the companion Paper XX of this series to explore the variation of global galaxy properties, including the IMF, on the projections of the MP.

An extensive catalogue of early-type galaxies in the nearby Universe

“…If σe is available for a given ETG in the catalogue, but σ0 is not, the relation log 10 σ0 km/s = 1.0478 log 10 σe km/s − 0.0909 (11) is used in order to estimate σ0 from σe. This equation is obtained from a least-squares fit to data on 260 ETGs in Cappellari et al (2013), while taking their data on the velocity dispersions within the central parsec of the ETGs as a measure for σ0. Swapping σ0 and σe in the fit leads to log 10 σe km/s = 0.9251 log 10 σ0 km/s + 0.1485, (12) which is used to estimate σe from σ0, if only σ0 has been found in the literature for a given galaxy.…”

“…The number in this column is set to '0' if no data on σe is available. A '1' in column 11 indicates that the galaxy is included in the ATLAS 3D survey, and that the value for σe is taken from Cappellari et al (2013). A '2' indicates that σe is from Forbes et al (2011), a '3' that σe is from Guérou et al (2015), a '4' that σe is from Toloba et al (2014), a '5' that σe is from Geha et al (2003), a '6' that σe is from , a '7' that σe is from Chilingarian et al (2008), a '8' that σe is from Scodeggio et al (1998b), a '9' that σe is from Thomas et al (2005), a '10' that σe is from Matković et al (2009), and a '11' that σe is from Sánchez-Blázquez et al (2006).…”

The Massive Survey. Iv. The X-Ray Halos of the Most Massive Early-Type Galaxies in the Nearby Universe

“…Earlier work has focused on the ATLAS 3D sample (e.g., Emsellem et al 2011;Krajnović et al 2011;Young et al 2011;Cappellari et al 2013), a volume-limited sample ( < D 42 Mpc) of all nearby early-type galaxies with < -M 21.5 K mag. Using the ATLAS 3D galaxies, there has been suggestive evidence that galaxies with net rotation (i.e., fast rotators) have lower L X than slow rotators at a given stellar mass.…”

Implications of a variable IMF for the interpretation of observations of galaxy populations

“…Cappellari et al (2012Cappellari et al ( , 2013b report IMF variations that correlate with the stellar mass-to-light ratio inferred from SED modelling under the assumption of a universal IMF and also with the effective velocity dispersion of the ETGs, but not with age, metallicity or alphaenhancement (McDermid et al 2014). However, Clauwens, Schaye & Franx (2015) show that the inferred IMF variations could be caused by a slight underestimation of the modeling-and measurement errors.…”