English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Projection effects, whereby galaxies along the line-of-sight to a galaxycluster are mistakenly associated with the cluster halo, present a significantchallenge for optical cluster cosmology. We use statistically representativespectral coverage of luminous galaxies to investigate how projection effectsimpact the low-redshift limit of the Sloan Digital Sky Survey (SDSS) redMaPPergalaxy cluster catalogue. Spectroscopic redshifts enable us to differentiatetrue cluster members from false positives and determine the fraction ofcandidate cluster members viewed in projection. Our main results can besummarized as follows: first, we show that a simple double-Gaussian model canbe used to describe the distribution of line-of-sight velocities in theredMaPPer sample; second, the incidence of projection effects is substantial,accounting for $\sim 16$ per cent of the weighted richness for the lowestrichness objects; third, projection effects are a strong function of richness,with the contribution in the highest richness bin being several times smallerthan for low-richness objects; fourth, our measurement has a similar amplitudeto state-of-the-art models, but finds a steeper dependence of projectioneffects on richness than these models; and fifth, the slope of the observedvelocity dispersion--richness relation, corrected for projection effects,implies an approximately linear relationship between the true,three-dimensional halo mass and three-dimensional richness. Our results providea robust, empirical description of the impact of projection effects on the SDSSredMaPPer cluster sample and exemplify the synergies between optical imagingand spectroscopic data for studies of galaxy cluster astrophysics andcosmology.

Spectroscopic Quantification of Projection Effects in the SDSS redMaPPer Galaxy Cluster Catalogue