Galaxy Cluster Mass Estimation from Stacked Spectroscopic Analysis
Arya Farahi, August E. Evrard, Eduardo Rozo, Eli S. Rykoff, Risa H. Wechsler
Abstract
We use simulated galaxy surveys to study: i) how galaxy membership in redMaPPer clusters maps to the underlying halo population, and ii) the accuracy of a mean dynamical cluster mass,
M
σ
(λ)
, derived from stacked pairwise spectroscopy of clusters with richness
λ
. Using
∼130,000
galaxy pairs patterned after the SDSS redMaPPer cluster sample study of Rozo et al. (2015 RMIV), we show that the pairwise velocity PDF of central--satellite pairs with
m
i
<19
in the simulation matches the form seen in RMIV. Through joint membership matching, we deconstruct the main Gaussian velocity component into its halo contributions, finding that the top-ranked halo contributes
∼60%
of the stacked signal. The halo mass scale inferred by applying the virial scaling of Evrard et al. (2008) to the velocity normalization matches, to within a few percent, the log-mean halo mass derived through galaxy membership matching. We apply this approach, along with mis-centering and galaxy velocity bias corrections, to estimate the log-mean matched halo mass at
z=0.2
of SDSS redMaPPer clusters. Employing the velocity bias constraints of Guo et al. (2015), we find
⟨ln(
M
200c
)|λ⟩=ln(
M
30
)+
α
m
ln(λ/30)
with
M
30
=1.56±0.35×
10
14
M
⊙
and
α
m
=1.31±
0.06
stat
±
0.13
sys
. Systematic uncertainty in the velocity bias of satellite galaxies overwhelmingly dominates the error budget.