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arXiv · astro-ph/9912412

Detecting the Gravitational Redshift of Cluster Gas

Tom Broadhurst·Evan Scannapieco
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Abstract

We examine the gravitational redshift of radiation emitted from within the potential of a cluster. Spectral lines from the intracluster medium (ICM) are redshifted in proportion to the emission-weighted mean potential along the line of sight, amounting to approximately 50 km/s at a radius of 100 kpc/h, for a cluster dispersion of 1200 km/s. We show that the relative redshifts of different ionization states of metals in the ICM provide a unique probe of the three-dimensional matter distribution. An examination of the reported peculiar velocities of cD galaxies in well studied Abell clusters reveals they are typically redshifted by an average of $\sim +200$ km/s. This can be achieved by gravity with the addition of a steep central potential associated with the cD galaxy. Note that in general gravitational redshifts cause a small overestimate of the recessional velocities of clusters by an average of $\sim$ 20 km/s.

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Tom Broadhurst, Evan Scannapieco. 2000-03-08. Detecting the Gravitational Redshift of Cluster Gas. https://doi.org/10.1086/312630

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