Modelling redshift space distortion in the post-reionization HI 21-cm power spectrum

Debanjan Sarkar, Somnath Bharadwaj

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


The post-reionization HI 21-cm signal is an excellent candidate for precision cosmology, this however requires accurate modelling of the expected signal. Sarkar et al. have simulated the real space HI 21-cm signal and have modelled the HI power spectrum as PHI(k) = b2P(k), where P(k) is the dark matter power spectrum and b(k) is a (possibly complex) scale-dependent bias for which fitting formulas have been provided. This paper extends these simulations to incorporate redshift space distortion and predicts the expected redshift space HI 21-cm power spectrum Ps HI(k, k) using two different prescriptions for the HI distributions and peculiar velocities. We model Ps HI(k, k), assuming that it is the product of PHI(k) = b2P(k) with a Kaiser enhancement term and a Finger of God (FoG) damping which has σp the pair velocity dispersion as a free parameter. Considering several possibilities for the bias and the damping profile, we find that the models with a scale-dependent bias and a Lorentzian damping profile best fit the simulated Ps HI(k, k) over the entire range 1 ≤ z ≤ 6. The best-fitting value of σp falls approximately as (1 + z)-m with m = 2 and 1.2, respectively, for the two different prescriptions. The model predictions are consistent with the simulations for k < 0.3Mpc-1 over the entire z range for the monopole Ps 0(k), and at z ≤ 3 for the quadrupole Ps 2(k). At z ≥ 4 the models underpredict Ps 2(k) at large k, and the fit is restricted to k < 0.15 Mpc-1.

Original languageEnglish
Pages (from-to)96-108
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - 1 May 2018
Externally publishedYes


  • Cosmology: theory
  • Diffuse radiation
  • Large-scale structure of Universe
  • Methods: statistical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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