Detecting the gravitational redshift of cluster gas

Tom Broadhurst, Evan Scannapieco

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


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 ≈50 km s-1 at a radius of 100 kpc h-1, for a cluster dispersion of 1200 km s-1. 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 that they are typically redshifted by an average of ∼200 km s-1. 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 ∼20 km s-1.

Original languageEnglish (US)
Pages (from-to)L93-L97
JournalAstrophysical Journal
Issue number2 PART 2
StatePublished - Apr 20 2000
Externally publishedYes


  • Cosmology: observations
  • Galaxies: clusters: general
  • Techniques: spectroscopic
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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