The galaxy–subhalo connection in low-redshift galaxy clusters from weak gravitational lensing

Abstract

We measure the gravitational lensing signal around satellite galaxies in a sample of galaxy clusters at z < 0.15 by combining high-quality imaging data from the Canada-France-Hawaii Telescope with a large sample of spectroscopically-confirmed cluster members. We use extensive image simulations to assess the accuracy of shape measurements of faint, background sources in the vicinity of bright satellite galaxies. We find a small but significant bias, as light from the lenses makes the shapes of background galaxies appear radially aligned with the lens. We account for this bias by applying a correction that depends on both lens size and magnitude. We also correct for contamination of the source sample by cluster members. We use a physically-motivated definition of subhalo mass, namely the mass bound to the subhalo, m bg , similar to definitions used by common subhalo finders in numerical simulations. Binning the satellites by stellar mass we provide a direct measurement of the subhalo-to-stellar-mass relation, log m bg /M = (11.54 ± 0.05) + (0.95 ± 0.10) log[m /(2 × 10 10 M )]. This best-fitting relation implies that, at a stellar mass m ∼ 3 × 10 10 M , subhalo masses are roughly 50 per cent of those of central galaxies, and this fraction decreases at higher stellar masses. We find some evidence for a sharp change in the total-to-stellar mass ratio around the clusters' scale radius, which could be interpreted as galaxies within the scale radius having suffered more strongly from tidal stripping, but remain cautious regarding this interpretation.

KiDS+GAMA: The weak lensing calibrated stellar-to-halo mass relation of central and satellite galaxies

“…results. We also need to point out, as mentioned by Sifón et al (2018), that the measurements from Zu & Mandelbaum (2015) and Mandelbaum et al (2016) agree perfectly when the galaxies between the two samples are matched. The SMHM relations of Leauthaud et al (2012), Moster et al (2013), andHudson et al (2015) can be considered as better comparisons than the ones from the EAGLE or Illustris TNG simulations since they are obtained at redshifts comparable to the redshifts of the GAMA galaxies.…”

“…Similarly, for satellites, we show in Fig. 9 the comparison of the results from Rodríguez-Puebla et al (2013), Sifón et al (2018), and the EAGLE simulation with our two methods. However, the definitions of the halo mass of satellite galaxies in both Rodríguez-Puebla et al (2013) and Sifón et al (2018) are not equivalent to the one we use throughout this paper and it is also hard to correct this in order to compare the same quantities.…”

“…Similarly, Pastor Mira et al (2011) found that the NFW profile is a better fit than truncated profiles for subhaloes in the Millennium Simulation (Springel et al 2005), and that the reduction in mass produced by tidal stripping is simply reflected as a change in the NFW concentration of subhaloes. Following Sifón et al (2018), we have decided to model both centrals and satellites using the NFW profile, but while allowing the concentrations to differ.…”

“…While the SMHM relation of central galaxies has been successfully measured by many studies (for instance by Hoekstra et al 2005;Mandelbaum et al 2006;More et al 2011;van Uitert et al 2011;Leauthaud et al 2012), this is not the case for satellite galaxies whose SMHM relation remains essentially unconstrained (Sifón et al 2018). Recently, several weak gravitational lensing studies using galaxy groups and clusters have been undertaken (such as the ones by Limousin et al 2007;Li et al 2014Li et al , 2016Sifón et al 2015Sifón et al , 2018, all of them finding that the satellite galaxies' haloes are heavily truncated with respect to the central and field ones.…”

“…Weak gravitational lensing, through the lensing of background sources by a sample of galaxies, which is commonly called galaxy-galaxy lensing, directly measures the total mass of lensing galaxies, without assuming their dynamical state (Bartelmann & Schneider 2001;Courteau et al 2014), and it is currently the only method available to measure the total mass of samples of galaxies directly. Measuring the lensing signal around satellite galaxies, however, can be particularly challenging for several reasons: their small contribution to the lensing signal by the host galaxy group, source blending at small separations, and sensitivity to field galaxy contamination (Sifón et al 2018). As pointed out by Sifón et al (2015), the latter point is rather important as the field galaxies are not stripped and their contamination therefore complicates the interpretation of the lensing signal.…”