Galaxy-galaxy lensing constraints on the relation between baryons and dark matter in galaxies in the Red Sequence Cluster Survey 2

Abstract

We present the results of a study of weak gravitational lensing by galaxies using imaging data that were obtained as part of the second Red Sequence Cluster Survey (RCS2). In order to compare to the baryonic properties of the lenses we focus here on the ∼300 square degrees that overlap with the data release 7 (DR7) of the Sloan Digital Sky Survey (SDSS). The depth and image quality of the RCS2 enables us to significantly improve upon earlier work for luminous galaxies at z ≥ 0.3. To model the lensing signal we employ a halo model which accounts for the clustering of the lenses and distinguishes between satellite and central galaxies. Comparison with dynamical masses from the SDSS shows a good correlation with the lensing mass for early-type galaxies. The correlation is less clear for late-type galaxies, possibly due to rotation. For low luminosity (stellar mass) early-type galaxies we find a satellite fraction of ∼40% which rapidly decreases to <10% with increasing luminosity (stellar mass). The satellite fraction of the late-types has a value in the range 0-15%, independent of luminosity or stellar mass. At high masses the satellite fraction is not well constrained, which we partly attribute to the modelling assumptions. To infer virial masses we apply simple models based on an independent satellite kinematics analysis to account for intrinsic scatter in the scaling relations. We find that early-types in the range 10 10 < L r < 10 11.5 L have virial masses that are about five times higher than those of late-type galaxies and that the mass scales as M 200 ∝ L 2.34 +0.09 −0.16 . For an early-type galaxy with a fiducal luminosity of 10 11 L r, , we obtain a mass M 200 = (1.93 +0.13 −0.14 ) × 10 13 h −1 M . We also measure the virial mass-to-light ratio, and find for L 200 < 10 11 L a value of M 200 /L 200 = 42 ± 10 for early-types, which increases for higher luminosities to values that are consistent with those observed for groups and clusters of galaxies. For late-type galaxies we find a lower value of M 200 /L 200 = 17 ± 9. Our measurements also show that early-and late-type galaxies have comparable halo masses for stellar masses M * < 10 11 M , whereas the virial masses of early-type galaxies are higher for higher stellar masses. To compare the efficiency with which baryons have been converted into stars, we determine the total stellar mass within r 200 . Our results for early-type galaxies suggest a variation in efficiency with a minimum of ∼10% for a stellar mass M * ,200 = 10 12 M . The results for the late-type galaxies are not well constrained, but do suggest a larger value.

Evolution of the luminosity-to-halo mass relation of LRGs from a combined analysis of SDSS-DR10+RCS2

“…As in van Uitert et al (2011Uitert et al ( , 2013, Cacciato et al (2014), we used the greater number of ancillary data on galaxies that is available from the SDSS compared with the RCS2 because the SDSS features photometry in five optical bands and includes spectroscopy for over a million of galaxies. However, the RCS2 imaging is ∼2 mag deeper and achieved a median seeing of approximately 0.7 , compared to 1.2 for SDSS, therefore the RCS2 is better suited for a weak-lensing analysis of lenses at higher redshifts.…”

Stellar mass versus velocity dispersion as tracers of the lensing signal around bulge-dominated galaxies

“…The magnitudes are calibrated using the colours of the stellar locus and the overlapping Two-Micron All-Sky Survey (2MASS), and they are accurate to <0.03 mag in each band compared to the SDSS. The creation of the galaxy shape catalogues is described in detail in van Uitert et al (2011). We refer readers to that paper for more detail, and present here a short summary of the most important steps.…”

“…Based on the range of stellar masses and velocity dispersions of our lenses, we expect the majority of our lenses to be central galaxies (see, e.g. van Uitert et al 2011;or Mandelbaum et al 2006, for estimates of the satellite fraction for galaxies in these ranges) that are considerably more massive than the average galaxy. The range over which the lensing signal is therefore described well by an SIS is likely even broader for our lenses.…”

“…The relation between the stellar mass and the total mass of galaxies has been studied with observations (e.g. Mandelbaum et al 2006;van Uitert et al 2011;Leauthaud et al 2012;More et al 2011;Wake et al 2011), abundance-matching techniques (e.g. Behroozi et al 2010;Guo et al 2010;Moster et al 2010), semi-analytical modelling (e.g.…”

“…Another property of galaxies that is related to the total mass is the velocity dispersion, which is the luminosityweighted dispersion of the motions of stars along the line-ofsight within a spectroscopic aperture. The velocity dispersion provides a dynamical estimate of the central mass and correlates with the stellar mass (Taylor et al 2010) and the total mass of galaxies (van Uitert et al 2011).…”