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

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### 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.

### Most cited references1

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### Gravitational redshift of galaxies in clusters as predicted by general relativity

(2011)
The theoretical framework of cosmology is mainly defined by gravity, of which general relativity is the current model. Recent tests of general relativity within the \Lambda Cold Dark Matter (CDM) model have found a concordance between predictions and the observations of the growth rate and clustering of the cosmic web. General relativity has not hitherto been tested on cosmological scales independent of the assumptions of the \Lambda CDM model. Here we report observation of the gravitational redshift of light coming from galaxies in clusters at the 99 per cent confidence level, based upon archival data. The measurement agrees with the predictions of general relativity and its modification created to explain cosmic acceleration without the need for dark energy (f(R) theory), but is inconsistent with alternative models designed to avoid the presence of dark matter.
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### Author and article information

###### Journal
2014-10-20
2015-02-20
###### Article
10.1103/PhysRevLett.114.071103
1410.5262

Phys. Rev. Lett. 114, 071103 (2015)
5 pages, 1 figure; v2 - version published in PRL
astro-ph.CO

Cosmology & Extragalactic astrophysics