Streaming Velocities and the Baryon Acoustic Oscillation Scale

Abstract

At the epoch of decoupling, cosmic baryons had supersonic velocities relative to the dark matter that were coherent on large scales. These velocities subsequently slow the growth of small-scale structure and, via feedback processes, can influence the formation of larger galaxies. We examine the effect of streaming velocities on the galaxy correlation function, including all leading-order contributions for the first time. We find that the impact on the BAO peak is dramatically enhanced (by a factor of ∼ 5) over the results of previous investigations, with the primary new effect due to advection: if a galaxy retains memory of the primordial streaming velocity, it does so at its Lagrangian, rather than Eulerian, position. Since correlations in the streaming velocity change rapidly at the BAO scale, this advection term can cause a significant shift in the observed BAO position. If streaming velocities impact tracer density at the 1% level, compared to the linear bias, the recovered BAO scale is shifted by approximately 0.5%. This new effect, which is required to preserve Galilean invariance, greatly increases the importance of including streaming velocities in the analysis of upcoming BAO measurements and opens a new window to the astrophysics of galaxy formation.

Constraining the relative velocity effect using the Baryon Oscillation Spectroscopic Survey

“…In Alam et al (2016) the potential impact of the relative velocity effect on the BOSS-DR12 BAO measurement has been investigated using a configuration-space model following Blazek, McEwen & Hirata (2015). The potential shift in the isotropic BAO scale (α) has been limited to 0.3σ, which is consistent with our results for b v 2 .…”

“…We derive all redshift-space 1-loop terms for the relative velocity, extending models used in previous analysis (see appendix A). For the first time we include the advection terms as suggested in Blazek, McEwen & Hirata (2015). An analysis without the advection term is presented in Yoo & Seljak (2013).…”

“…We follow the nomenclature of Blazek, McEwen & Hirata (2015) meaning that our velocity bias b v 2 is a factor of 3 times smaller compared to Yoo & Seljak (2013). A list of all terms in eq.…”

“…terms following the approach of Yoo, Dalal & Seljak (2011) and Blazek, McEwen & Hirata (2015) with the addition of redshift-space distortion terms, which describe the couplings of the density field with the velocity divergence field. We also include the linear terms P δ|δ bc (k) and P δ|θ bc (k) as discussed in Schmidt (2016).…”

“…While such studies have been done before, there are several novel aspects to our analysis: (1) for the first time we include the advection term (Blazek, McEwen & Hirata 2015), (2) beside b v 2 we also set constraints on biasing by the density, δ bc and velocity divergence, θ bc (Barkana & Loeb 2011;Schmidt 2016), (3) we include all relative velocity contributions up to 1-loop order including the redshift-space terms and (4) we quantify the potential shifts due to all three relative velocity contributions for the anisotropic BAO and RSD parameters.…”