Do gas-poor galaxy clusters have different galaxy populations? The positive covariance of hot and cold baryons

Galaxy clusters show a variety of intracluster medium properties at a fixed mass in gas fractions, X-ray luminosity and X-ray surface brightness. In this work, we investigate whether the yet-undetermined cause that produces clusters of X-ray low surface brightness also affects galaxy properties, such as richness, richness concentration, width and location of the red sequence, colour, luminosity, and dominance of the brightest cluster galaxy. We use Sloan Digital Sky Survey Data Release 12 photometry, and our analysis factors out the mass dependency to derive trends at fixed cluster mass. Clusters of low surface brightness for their mass have cluster richness in spite of their group-like luminosity. Gas-poor, low X-ray surface brightness, X-ray faint clusters for their mass display 25 per cent lower richness for their mass at the 4.4 sigma level. Therefore, richness and quantities depending on gas, such as gas fraction, M-gas and X-ray surface brightness, are covariant at fixed halo mass. In particular, we do not confirm the suggestion of anticorrelation of hot and cold baryons at fixed mass put forth in the literature. All the remaining optical properties show no covariance at fixed mass, within the sensitivities allowed by our data and sample size. We conclude that X-ray and optical properties are disjointed; the optical properties do not show signatures of those processes involving gas content, apart from the richness-mass scaling relation. The covariance between X-ray surface brightness and richness is useful for an effective X-ray follow-up of low-surface-brightness clusters because it allows us to pre-select clusters using optical data of survey quality and avoids expensive X-ray observations.