How Density Environment Changes the Influence of the Dark Matter-Baryon Streaming Velocity on the Cosmological Structure Formation

Abstract

We study the dynamical effect of relative velocities between dark matter and baryonic fluids, which remained supersonic after the epoch of recombination. The impact of this supersonic motion on the formation of cosmological structures was first formulated by Tseliakhovich & Hirata (2010), in terms of the linear theory of small-scale fluctuations coupled to large-scale, relative velocities in mean-density regions. In their formalism, they limited the large-scale density environment to be those of the global mean density. We improve on their formulation by allowing variation in the density environment as well as the relative velocities. This leads to a new type of coupling between large-scale and small-scale modes. We find that the small-scale fluctuation grows in a biased way: faster in the overdense environment and slower in the underdense environment. We also find that the net effect on the global power spectrum of the density fluctuation is to boost its overall amplitude from the prediction by Tseliakhovich & Hirata (2010). Correspondingly, the conditional mass function of cosmological halos and the halo bias parameter are both affected in a similar way. The discrepancy between our prediction and that by Tseliakhovich & Hirata (2010) is significant, and therefore the related cosmology and high-redshift astrophysics should be revisited. The mathematical formalism of this study can be used for generating cosmological initial conditions of small-scale perturbations in generic, overdense (underdense) background patches.

Accepted for publication in ApJ; Significant quantitative improvement including all the normal modes (growing, decaying, streaming, compensated) for large-scale perturbations from v1; minor typo corrections from v2

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• Higher-order initial conditions for mixed baryon-CDM simulations
• Galaxy bias and primordial non-Gaussianity: insights from galaxy formation simulations with IllustrisTNG
• Formation of the first star clusters and massive star binaries by fragmentation of filamentary primordial gas clouds
• Baryon-CDM isocurvature galaxy bias with IllustrisTNG
• Cosmological advection flows in the presence of primordial black holes as dark matter and formation of first sources
• Cosmic Reionization May Still Have Started Early and Ended Late: Confronting Early Onset with CMB Anisotropy and 21 cm Global Signals
• The Supersonic Project: rotational effects of supersonic motions on the first structures in the Universe
• Large-scale variation in reionization history caused by Baryon-dark matter streaming velocity
• First Structure Formation under the Influence of Gas-Dark Matter Streaming Velocity and Density: Impact of the Baryons-trace-dark matter Approximation
• Imprints of Reionization in Galaxy Clustering
• A Model-Insensitive Baryon Acoustic Oscillation Feature in the 21 cm Signal from Reionization
• Compensated Isocurvature Perturbations in the Galaxy Power Spectrum
• Formation of First Galaxies inside Density Peaks and Voids under the Influence of Dark Matter-Baryon Streaming Velocity, I: Initial Condition and Simulation Scheme
• The effect of Primordial Black Holes and streaming motions on structure formation
• Relative baryon-dark matter velocities in cosmological zoom simulations
• The influence of baryons on low-mass haloes
• Cosmic voids and BAO with relative baryon-CDM perturbations