A Caltech Library Service

Relative velocity of dark matter and baryonic fluids and the formation of the first structures

Tseliakhovich, Dmitriy and Hirata, Christopher (2010) Relative velocity of dark matter and baryonic fluids and the formation of the first structures. Physical Review D, 82 (8). Art. No. 083520. ISSN 1550-7998.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


At the time of recombination, baryons and photons decoupled and the sound speed in the baryonic fluid dropped from relativistic, ~c/√3, to the thermal velocities of the hydrogen atoms, ~2×10^(-5)c. This is less than the relative velocities of baryons and dark matter computed via linear perturbation theory, so we infer that there are supersonic coherent flows of the baryons relative to the underlying potential wells created by the dark matter. As a result, the advection of small-scale perturbations (near the baryonic Jeans scale) by large-scale velocity flows is important for the formation of the first structures. This effect involves a quadratic term in the cosmological perturbation theory equations and hence has not been included in studies based on linear perturbation theory. We show that the relative motion suppresses the abundance of the first bound objects, even if one only investigates dark matter haloes, and leads to qualitative changes in their spatial distribution, such as introducing scale-dependent bias and stochasticity. We further discuss the possible observable implications of this effect for high-redshift galaxy clustering and reionization.

Item Type:Article
Related URLs:
URLURL TypeDescription
Hirata, Christopher0000-0002-2951-4932
Additional Information:© 2010 American Physical Society. Received 24 May 2010; published 18 October 2010. We thank Neal Dalal, Eiichiro Komatsu, Kiyoshi Masui, Leonidas Moustakas, Michael Kuhlen, and Ue-Li Pen for helpful conversations. D. T. and C. H. are supported by the U.S. Department of Energy (DE-FG03-92-ER40701) and the National Science Foundation (AST-0807337). C. H. is supported by the Alfred P. Sloan Foundation.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-92-ER40701
Alfred P. Sloan FoundationUNSPECIFIED
Issue or Number:8
Classification Code:PACS: 98.65.Dx, 98.80.Es
Record Number:CaltechAUTHORS:20101108-100254067
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20707
Deposited By: Jason Perez
Deposited On:09 Nov 2010 17:56
Last Modified:03 Oct 2019 02:13

Repository Staff Only: item control page