Cross-Correlation Weak Lensing of SDSS Galaxy Clusters. Iii. Mass-to-Light Ratios

Abstract

We present measurements of the excess mass-to-light ratio measured around MaxBCG galaxy clusters observed in the SDSS. This red sequence cluster sample includes objects from small groups with M 200 ∼ 5 × 10 12 h −1 M ⊙ to clusters with M 200 ∼ 10 15 h −1 M ⊙ . Using cross-correlation weak lensing, we measure the excess mass density profile above the universal mean ∆ρ(r) = ρ(r) −ρ for clusters in bins of richness and optical luminosity. We also measure the excess luminosity density ∆ℓ(r) = ℓ(r) −l measured in the z = 0.25 i-band. For both mass and light, we de-project the profiles to produce 3D mass and light profiles over scales from 25h −1 kpc to 22h −1 Mpc. From these profiles we calculate the cumulative excess mass ∆M (r) and excess light ∆L(r) as a function of separation from the BCG. On small scales, where ρ(r) ≫ρ, the integrated mass-to-light profile (∆M/∆L)(r) may be interpreted as the cluster mass-to-light ratio. We find the (∆M/∆L) 200 , the mass-to-light ratio within r 200 , scales with cluster mass as a power law with index 0.33 ± 0.02. On large scales, where ρ(r) ∼ρ, the ∆M/∆L approaches an asymptotic value independent of cluster richness. For small groups, the mean (∆M/∆L) 200 is much smaller than the asymptotic value, while for large clusters (∆M/∆L) 200 is consistent with the asymptotic value. This asymptotic value should be proportional to the mean mass-to-light ratio of the universe M/L . We find M/L b −2 M/L = 362 ± 54h (statistical). There is additional uncertainty in the overall calibration at the ∼10% level. The parameter b 2 M/L is primarily a function of the bias of the L L * galaxies used as light tracers, and should be of order unity. Multiplying by the luminosity density in the same bandpass we find Ω m b −2 M/L = 0.20 ± 0.03, independent of the Hubble parameter.

J0454-0309: evidence of a strong lensing fossil group falling into a poor galaxy cluster

“…For a cluster with the same number of N 200 (Sect. 4.3) galaxies as J0454, Sheldon et al (2009a) predict M 200 /L0.25 i = 200 ± 30 h. Given the scatter present in the luminosity and the mass of a given N 200 bin (see Sheldon et al 2009b,a), J0454 does not appear exceptionally over-luminous compared to non-fossil systems. The contribution of the BGG to the total luminosity in i-band within r 200 is 38%.…”

“…This also applies to J0454, for which the data are insufficient to derive a temperature map with sufficient resolution to establish the non-existence of a cooling core. Sheldon et al (2009a) have obtained mass-to-light ratios for the maxBCG cluster sample in SDSS, using weak lensing to estimate M 200 . The total luminosity within r 200 was inferred from red sequence galaxies only.…”

Characterising superclusters with the galaxy cluster distribution

“…From the observations and simulations we have a good understanding of the relation between cluster observables and the total mass of a cluster, for instance Böhringer et al (2012), Sheldon et al (2009), andJohnston et al (2007), which means that the visible components of a cluster represent the underlying dark matter component well. If DM had no preferential scale, this argument should apply in a similar way to superclusters, which means that a supercluster mass probed by the total cluster mass is probably also correlated with the true mass of the supercluster.…”

The environmental dependence of the stellar mass function atz~ 1

“…We integrate these NFW profiles along the LOS and out to a projected radius of 1 Mpc, yielding a total mass of 5.6 × 10 15 M for the 10 clusters. Since Sheldon et al (2009) and Hoekstra et al (2000) have shown that, although cluster centres are dominated by luminous matter, the mass to light ratio (M/L) of clusters within a distance of 1 Mpc is similar to the cluster M/L within larger distances, this ensures that we measure and normalise the SMF in a representative volume. Figure 8 shows the total SMF for the cluster and the field, after normalising by the total masses estimated above.…”