Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStreaming Velocity Effects on the Post-reionization 21 cm Baryon Acoustic Oscillation Signal
99
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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 velocity on the BAO feature in HI 21 cm intensity mapping after reionization, with a focus on redshifts $3.5lesssim zlesssim5.5$. We build a spatially modulated halo model that includes the dependence of the filtering mass on the local reionization redshift and thermal history of the intergalactic gas. In our fiducial model, we find isotropic streaming velocity bias coefficients $b_v$ ranging from $-0.0033$ at $z=3.5$ to $-0.0248$ at $z=5.5$, which indicates that the BAO scale is stretched (i.e., the peaks shift to lower $k$). In particular, streaming velocity shifts the transverse BAO scale between 0.087% ($z=3.5$) and 0.37% ($z=5.5$) and shifts the radial BAO scale between 0.13% ($z=3.5$) and 0.52% ($z=5.5$). These shifts exceed the projected error bars from the more ambitious proposed hemispherical-scale surveys in HI (0.13% at $1sigma$ per $Delta z = 0.5$ bin).
rate research
Read More
We examine the impact of baryon-dark matter relative velocities on intergalactic small-scale structure and the 21 cm signal during reionization. Streaming velocities reduced clumping in the intergalactic medium (IGM) on mass scales of $sim 10^4 - 10^8$ M$_{odot}$. This effect produced a distinct baryon acoustic oscillation (BAO) feature in the 21 cm power spectrum at wave numbers $ksim 0.1$ h/Mpc, near which forthcoming surveys will be most sensitive. In contrast to the highly uncertain impact of streaming velocities on star formation, the effect on clumping is better constrained because it is set mainly by cosmology and straightforward gas dynamics. We quantify the latter using coupled radiation-hydrodynamic simulations that capture the Jeans scale of pre-reionization gas. The clumping factor of ionized gas is reduced by 5-10% in regions with RMS streaming velocities. The suppression peaks $approx 5$ Myr after a region is reionized, but disappears within 200 Myr due to pressure smoothing. We model the corresponding impact on the 21 cm signal and find that the BAO feature is most likely to appear at $approx$ 10 % ionization. During this phase, the feature may appear at the 1 % (5 %) level at $k sim 0.1 (0.06)$ h/Mpc with an amplitude that varies by a factor of $< 10$ across a range of reionization histories. We also provide a model for the signal originating from streaming velocitys impact on ionizing sources, which can vary by 4 orders of magnitude depending on highly uncertain source properties. We find that the clumping signal probably dominates the source one unless Population III star formation in $10^6 - 10^8$ M$_{odot}$ halos contributed significantly to the first 10% of reionization.
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 velocity on the BAO feature of the Lyman-$alpha$ forest auto-power spectrum, one of the main tracers being used by the recently commissioned DESI spectrograph. To do this, we develop a new perturbative model for Lyman-$alpha$ flux density contrast which is complete to second order for a certain set of fields, and applicable to any redshift-space tracer of structure since it is based only on symmetry considerations. We find that there are 8 biasing coefficients through second order. We find streaming velocity-induced shifts in the BAO scale of 0.081--0.149% (transverse direction) and 0.053--0.058% (radial direction), depending on the model for the biasing coefficients used. These are smaller than, but not negligible compared to, the DESI Lyman-$alpha$ BAO error budget, which is 0.46% on the overall scale. The sensitivity of these results to our choice of bias parameters underscores the need for future work to measure the higher-order biasing coefficients from simulations, especially for future experiments beyond DESI.
The motion of the solar system with respect to the cosmic rest frame modulates the monopole of the Epoch of Reionization 21-cm signal into a dipole. This dipole has a characteristic frequency dependence that is dominated by the frequency derivative of the monopole signal. We argue that although the signal is weaker by a factor of $sim100$, there are significant benefits in measuring the dipole. Most importantly, the direction of the cosmic velocity vector is known exquisitely well from the cosmic microwave background and is not aligned with the galaxy velocity vector that modulates the foreground monopole. Moreover, an experiment designed to measure a dipole can rely on differencing patches of the sky rather than making an absolute signal measurement, which helps with some systematic effects.
Measurement of fluctuations in diffuse HI 21 cm background radiation from the post-reionization epoch (z < 6) is a promising avenue to probe the large-scale structure of the Universe and understand the evolution of galaxies. We observe the European Large-Area ISO Survey-North 1 (ELAIS-N1) field at 300-500 MHz using the upgraded Giant Meterwave Radio Telescope (uGMRT) and employ the foreground avoidance technique to estimate the HI 21 cm power spectrum in the redshift range z = 1.96-3.58. Given the possible systematics that may remain in the data, we find the most stringent upper limits on the spherically averaged 21 cm power spectra at k~1.0 Mpc$^{-1}$ are (58.87 mK)$^2$, (61.49 mK)$^2$, (60.89 mK)$^2$, (105.85 mK)$^2$ at z = 1.96,2.19,2.62 and 3.58, respectively. We use this to constrain the product of neutral HI mass density (Omega_HI) and HI bias (b_HI) to the underlying dark matter density field, [Omega_HI*b_HI], as 0.09,0.11,0.12,0.24 at z=1.96,2.19,2.62,3.58, respectively. To the best of our knowledge these are the first limits on the HI 21 cm power spectra at the redshift range z = 1.96 - 3.58 and would play a significant role to constrain the models of galaxy formation and evolution.
Measurements of the post-reionization 21-cm bispectrum $B_{{rm HI}}(mathbf{k_1},mathbf{k_2},mathbf{k_3})$ using various upcoming intensity mapping experiments hold the potential for determining the cosmological parameters at a high level of precision. In this paper we have estimated the 21-cm bispectrum in the $z$ range $1 le z le 6$ using semi-numerical simulations of the neutral hydrogen (${rm HI}$) distribution. We determine the $k$ and $z$ range where the 21-cm bispectrum can be adequately modelled using the predictions of second order perturbation theory, and we use this to predict the redshift evolution of the linear and quadratic ${rm HI}$ bias parameters $b_1$ and $b_2$ respectively. The $b_1$ values are found to decreases nearly linearly with decreasing $z$, and are in good agreement with earlier predictions obtained by modelling the 21-cm power spectrum $P_{{rm HI}}(k)$. The $b_2$ values fall sharply with decreasing $z$, becomes zero at $z sim 3$ and attains a nearly constant value $b_2 approx - 0.36$ at $z<2$. We provide polynomial fitting formulas for $b_1$ and $b_2$ as functions of $z$. The modelling presented here is expected to be useful in future efforts to determine cosmological parameters and constrain primordial non-Gaussianity using the 21-cm bispectrum.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
