Gravitational Redshift of Galaxies in Clusters from the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic Survey

TL;DR

This study measures the gravitational redshift in galaxy clusters using SDSS and BOSS data, confirming predictions of general relativity with improved accounting for systematic effects.

Contribution

It provides a new measurement of gravitational redshift in galaxy clusters using larger datasets and refined analysis techniques.

Findings

Measured average relative redshift of -11 km/s in galaxy clusters.

Results are consistent with general relativity predictions.

Standard deviation larger due to systematic effects.

Abstract

The gravitational redshift effect allows one to directly probe the gravitational potential in clusters of galaxies. Following up on Wojtak et al. [Nature (London) 477, 567 (2011)], we present a new measurement. We take advantage of new data from the tenth data release of the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic Survey. We compare the spectroscopic redshift of the brightest cluster galaxies (BCGs) with that of galaxies at the outskirts of clusters, using a sample with an average cluster mass of $10^{14} M_{\odot}$. We find that these galaxies have an average relative redshift of -11 km/s compared with that of BCGs, with a standard deviation of +7 and -5 km/s. Our measurement is consistent with that of Wojtak et al. However, our derived standard deviation is larger, as we take into account various systematic effects, beyond the size of the dataset. The result is in good agreement with the predictions from general relativity.