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

By Dmitriy Tseliakhovich, C. Hirata. 2010

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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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/76ecb8971fb3fc2633930bf5ce7c75c4f602de20

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Citations in the corpus

Gravity and Large-Scale Nonlocal Bias (2012, background): “at early times z & 100 the relative velocity between the dark matter and baryons is typically supersonic [57, 58], and there might be a non-trivial component to the relation between dark matter and baryons on large scales due to isocurvature modes, see e.”
The GMRT Epoch of Reionization experiment: a new upper limit on the neutral hydrogen power spectrum at z≈ 8.6 (2010, background): “This fraction may even be substantially smaller due to non-perturbative velocity flows (Tseliakhovich & Hirata 2010; Dalal et al. 2010).”
The First Stars (2012, background): “Tseliakhovich & Hirata (2010) also show that the relative velocity between gas and dark matter acts to suppress the growth of small-scale structure in both components, and that because this effect is formally a second-order term in cosmological perturbation theory, it was not included in previous…”
THE BIRTH OF A GALAXY: PRIMORDIAL METAL ENRICHMENT AND STELLAR POPULATIONS (2010, background): “…2007; Smith et al. 2009), resulting from the CMB temperature floor, could be more prevalent, and 2) streaming gas velocities arising from the recombination epoch (Tseliakhovich & Hirata 2010) could suppress star formation in halos below 106M⊙ (Tseliakhovich et al. 2011; Greif et al. 2011b).”
Computing the Three-Point Correlation Function of Galaxies in $\mathcal{O}(N^2)$ Time (2015, methodology): “…to apply our algorithm and analysis approach to SDSS DR12, with the goals of assessing the presence of BAO features, measuring the linear and non-linear bias, and constraining the baryon-dark matter relative velocity (Tseliakhovich & Hirata 2010; Yoo, Dalal & Seljak 2011; Yoo & Seljak 2013; SE15).”
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: measuring DA and H at z = 0.57 from the baryon acoustic peak in the data release 9 spectroscopic galaxy sample (2013, background): “The only astrophysical bias effect known to single out the acoustic scale is the early universe streaming velocities identified by Tseliakhovich & Hirata (2010).”
Signatures of X-rays in the early Universe (2012, background): “…a handful of stars per halo), and was likely suppressed by heating and feedback processes (Haiman et al. 2000; Ricotti et al. 2001; Mesinger et al. 2006; Haiman & Bryan 2006; Tseliakhovich & Hirata 2010; O’Leary & McQuinn 2012; though Ahn et al. 2012 suggest the feedback could be self-regulating).”
The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological analysis of the DR12 galaxy sample (2016, methodology): “…shift in the acoustic peak due to a coupling of the low-redshift galaxy density field to the small relative velocity between baryons and cold dark matter at high redshift (Tseliakhovich & Hirata 2010; Dalal et al. 2010; Yoo et al. 2011; Slepian & Eisenstein 2015; Blazek et al. 2016; Schmidt 2016).”
21 cm cosmology in the 21st century (2011, background): “It was recently realized that the relative velocity between the baryons and dark matter exceeds the local sound speed (which drops dramatically from the relativistic value of c/ √ 3 to ∼√kBT/mp) leading to supersonic flows [126].”
The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: baryon acoustic oscillations in the Fourier space (2016, background): “& Seljak 2010; Tseliakhovich & Hirata 2010; Yoo, Dalal & Seljak 2011; Beutler et al. 2016).”
Observational probes of cosmic acceleration (2012, background): “A possible complication to galaxy biasing at the BAO scale was pointed out by Tseliakhovich and Hirata (2010) and Yoo et al. (2011).”
The clustering of galaxies in the sdss-iii baryon oscillation spectroscopic survey: Baryon acoustic oscillations in the data release 9 spectroscopic galaxy sample (2012, background): “However, the only physically motivated model known that does couple to the acoustic scale is that of Tseliakhovich & Hirata (2010), in which relative velocities between the baryons and dark matter at high redshift modulate the ability of the smallest haloes to trap gas.”
THE MASS SPECTRUM OF THE FIRST STARS (2014, background): “Streaming motion is the relative motion of the baryon to the dark matter at small scale (Tseliakhovich & Hirata 2010).”
Biased tracers and time evolution (2014, background): “In other words, velocity biases of the type vg = bvv + bvδδ v and so on are prohibited by the equivalence principle in the absence of entropic perturbations (which however can exist in standard cosmology for example in the form of baryon-dark matter relative velocities [18]).”