We study the effect of the relative velocity between the dark matter (DM) and the baryon on the 21cm forest signals. The DM-baryon relative velocity arises due to their different evolutions before the baryon-photon decoupling epoch and it gives an additional anisotropic pressure that can suppress the perturbation growth. It is intriguing that the scales $k\sim {\cal O}(10\sim 10^3)h/\mathrm{Mpc}$ at which the matter power spectrum is affected by such a streaming velocity turns out to be the scale at which the 21cm forest signal is sensitive to. We demonstrate that the 21cm absorption line abundance can decrease by more than a factor of a few due to the small-scale matter power spectrum suppression caused by the DM-baryon relative velocity.
The Effect of Interstellar Absorption on Measurements of the Baryon Acoustic Peak in the Lyman-α Forest
近年来，人们利用氢Lyman-α森林的自相关性，利用BOSS巡天的数万条类星体谱，观测到了红移2 < z < 3.5的重子声峰。然而，银河系的星际介质会将吸收线引入任何河外源的光谱中。这些谱线虽然很弱，在单一BOSS光谱中无法检测到，但可能会使宇宙学信号产生偏差。为了检验这一点，我们通过叠加超过一百万个星系和类星体的光谱来生成吸收线图。我们发现，系统介绍太小，影响目前的重子声学峰值的准确性，但可能是相关的未来调查，如暗能量光谱仪（DESI）。我们概述了一种方法来解释这与未来的数据集。
We study and compare fitting methods for the Lyman-$α$ (Ly$α$) forest 3D correlation function. We use the nested sampler PolyChord and the community code picca to perform a Bayesian analysis which we compare with previous frequentist analyses. By studying synthetic correlation functions, we find that the frequentist profile likelihood produces results in good agreement with a full Bayesian analysis. On the other hand, Maximum Likelihood Estimation with the Gaussian approximation for the uncertainties is inadequate for current data sets. We compute for the first time the full posterior distribu…
Fitting Methods for Baryon Acoustic Oscillations in the Lyman-α Forest Fluctuations in BOSS Data Release 9
描述了分析莱曼-α森林涨落和测量重子声学振荡（BAO）参数的拟合方法。我们将我们的方法应用于BOSS Data Release 9。我们的方法是基于物理坐标空间中的三维关联函数模型，并包括红移空间失真，各向异性非线性展宽，和宽带失真的影响。我们允许独立的尺度因子沿和垂直的视线，以尽量减少对我们假设的基准宇宙学的依赖，并获得单独的测量的BAO角和相对速度尺度。我们的拟合软件和复制我们的主要BOSS数据版本9结果所需的输入文件是公开的。
The baryon acoustic oscillation (BAO) scale acts as a standard ruler for measuring cosmological distances and has therefore emerged as a leading probe of cosmic expansion history. However, any physical effect that alters the length of the ruler can lead to a bias in our determination of distance and expansion rate. One of these physical effects is the streaming velocity, the relative velocity between baryons and dark matter in the early Universe, which couples to the BAO scale due to their common origin in acoustic waves at recombination. In this work, we investigate the impact of streaming ve…
We present a measurement of baryonic acoustic oscillations (BAO) from Lyman-$α$ (Ly$α$) absorption and quasars at an effective redshift $z=2.33$ using the complete extended Baryonic Oscillation Spectroscopic Survey (eBOSS). The sixteenth and final eBOSS data release (SDSS DR16) contains all data from eBOSS and its predecessor, the Baryonic Oscillation Spectroscopic Survey (BOSS), providing $210,005$ quasars with $z_{q}>2.10$ that are used to measure Ly$α$ absorption. We measure the BAO scale both in the auto-correlation of Ly$α$ absorption and in its cross correlation with $341,468$ quasars wi…
We present the cosmological constraints on the cross section of baryon-dark matter interactions for the dark matter mass below the MeV scale from the Planck CMB (cosmic microwave background) and SDSS (Sloan Digital Sky Survey) Lyman-$α$ forest data. To explore the dark matter mass $m_χ\lesssim 1$ MeV for which the dark matter's free-streaming effect can suppress the observable small scale density fluctuations, in addition to the acoustic oscillation damping in existence of the baryon-dark matter coupling, we apply the approximated treatment of dark matter free-streaming analogous to that of th…
The Lyman-alpha forest is a unique probe of large-scale matter density fluctuations at high redshift (z > 2). It is possible to obtain 3D maps of the matter distribution from Lyman-alpha data, using tomographic reconstruction methods. Here, we present the largest tomographic map of matter fluctuations at z > 2, over the Gpc^3 volume covered by Lyman-alpha forest from SDSS-IV quasar spectra in the Stripe 82 field. We present a catalog of high-redshift voids constructed from this map. The measurement of the cross-correlation between these voids and the Lyman-alpha forest provides the first obser…
We present LyMAS2, an improved version of the "Lyman-α Mass Association Scheme" aiming at predicting the large-scale 3d clustering statistics of the Lyman-α forest (Ly-α) from moderate resolution simulations of the dark matter (DM) distribution, with prior calibrations from high resolution hydrodynamical simulations of smaller volumes. In this study, calibrations are derived from the Horizon-AGN suite simulations, (100 Mpc/h)^3 comoving volume, using Wiener filtering, combining information from dark matter density and velocity fields (i.e. velocity dispersion, vorticity, line of sight 1d-diver…
Observations of the Lyman-$α$ (Ly$α$) forest in spectra of distant quasars enable us to probe the matter power spectrum at relatively small scales. With several upcoming surveys, it is expected that there will be a many-fold increase in the quantity and quality of data, and hence it is important to develop efficient simulations to forward model these data sets. One such semi-numerical method is based on the assumption that the baryonic densities in the intergalactic medium (IGM) follow a lognormal distribution. In this work, we test the robustness of the lognormal model of the Ly$α$ forest in …
We present a systematic study of the cosmic variance that existed in the formation of first stars and galaxies. We focus on the cosmic variance induced by the large-scale density and velocity environment engraved at the epoch of recombination. The density environment is predominantly determined by the dark-matter overdensity, and the velocity environment by the dark matter-baryon streaming velocity. Toward this end, we introduce a new cosmological initial condition generator BCCOMICS, which solves the quasi-linear evolution of small-scale perturbations under the large-scale density and streami…
We explore the impact of baryonic effects (namely stellar and AGN feedback) on the moments of pairwise velocity using the Illustris-TNG, EAGLE, cosmo-OWLS, and BAHAMAS suites of cosmological hydrodynamical simulations. The assumption that the mean pairwise velocity of the gas component follows that of the dark matter is studied here at small separations, and we find that even at pair separations of 10-20 $h^{-1}\mathrm{Mpc}$ there is a 4-5% velocity bias. At smaller separations, it gets larger with strength varying depending on the subgrid prescription. By isolating different physical processe…
We revisit techniques for performing cosmological simulations with both baryons and cold dark matter when each fluid has different initial conditions, as is the case at the end of the radiation era. Most simulations do not reproduce the linear prediction for the difference between the cold dark matter and baryon perturbations. We show that this is due to the common use of offset regular grids when setting up the particle initial conditions. The correct behaviour can be obtained without any loss of simulation resolution by using a Lagrangian glass for the baryon particles. We further show that …
Baryon Acoustic Oscillations from the C IV Forest with DESI DR2
Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Boston University（波士顿大学）；Università degli Studi di Milano（米兰大学）；INAF-Osservatorio Astronomico di Brera（布拉耶天文台）；University College London（伦敦大学学院）；University of Portsmouth（朴茨茅斯大学）
DESI DR2 Baryon Acoustic Oscillations from the Lyman Alpha Forest Multipoles
The Ohio State University（俄亥俄州立大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Boston University（波士顿大学）；University of Rochester（罗切斯特大学）；Università degli Studi di Milano（米兰大学）；INAF-Osservatorio Astronomico di Brera（INAF-布雷拉天文台）；University College London（伦敦大学学院）
The relative velocity between baryons and dark matter in the early Universe can suppress the formation of small-scale baryonic structure and leave an imprint on the baryon acoustic oscillation (BAO) scale at low redshifts after reionization. This "streaming velocity" affects the post-reionization gas distribution by directly reducing the abundance of pre-existing mini-halos ($\lesssim 10^7 M_{\bigodot}$) that could be destroyed by reionization and indirectly modulating reionization history via photoionization within these mini-halos. In this work, we investigate the effect of streaming velocit…
At second-order, scalar perturbations can source traceless and transverse perturbations to the metric, called induced gravitational waves (IGW). The apparent gauge-dependence of the IGW obscures the interpretation of the stochastic gravitational-wave signal. To elucidate the gauge dependence, we study the IGW from manifestly gauge-invariant scalar perturbations, namely, the relative velocity between the baryon and cold dark matter. From this relative velocity perturbation, we compute the dimensionless gravitational wave power spectrum and the corresponding expected angular power spectrum of th…
