Gravitational redshifting of galaxies in the SPIDERS cluster catalogue. Issue 1 (26th February 2021)

• Record Type: Journal Article
• Authors: Mpetha, C T; Collins, C A; Clerc, N; Finoguenov, A; Peacock, J A; Comparat, J; Schneider, D; Capasso, R; Damsted, S; Furnell, K; Merloni, A; Padilla, N D; Saro, A
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 503:Issue 1(2021)
• Page Start: 669
• Page End: 678
• Publication Date: 2021-02-26
• Subjects: gravitation -- galaxies: clusters: general -- galaxies: kinematics and dynamics; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab544
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Data from the SPectroscopic IDentification of ERosita Sources (SPIDERS) are searched for a detection of the gravitational redshifting of light from ${\sim}20\, 000$ galaxies in ∼2500 galaxy clusters using three definitions of the cluster centre: its Brightest Cluster Galaxy (BCG), the redMaPPer identified Central Galaxy (CG), or the peak of X-ray emission. Distributions of velocity offsets between galaxies and their host cluster's centre, found using observed redshifts, are created. The quantity $\hat{\Delta }$, the average of the radial velocity difference between the cluster members and the cluster systemic velocity, reveals information on the size of a combination of effects on the observed redshift, dominated by gravitational redshifting. The change of $\hat{\Delta }$ with radial distance is predicted for SPIDERS galaxies in General Relativity (GR), and f ( R ) gravity, and compared to the observations. The values of $\hat{\Delta }=-13.5\pm 4.7$ km s −1, $\hat{\Delta }=-12.5\pm 5.1$ km s −1, and $\hat{\Delta }=-18.6\pm 4.8$ km s −1 for the BCG, X-ray, and CG cases, respectively, broadly agree with the literature. There is no significant preference of one gravity theory over another, but all cases give a clear detection (>2.5σ) of $\hat{\Delta }$ . The BCG centroid is deemed to be the most robust method in this analysis, due to no well-defined central redshift when using an X-ray centroid, and CGs identified by redMaPPer with no associated spectroscopic redshift. For future gravitational redshift studies, an order-of-magnitude more galaxies, ${\sim}500\, 000$, will be required – a possible feat with the forthcoming Vera C. Rubin Observatory, Euclid and eROSITA .