Post-reionization Signal Research Articles

Redshifted HI 21-cm Signal from the Post-Reionization Epoch: Cross-Correlations with Other Cosmological Probes

Tomographic intensity mapping of the HI using the redshifted 21 cm observations opens up a new window towards our understanding of cosmological background evolution and structure formation. This is a key science goal of several upcoming radio telescopes including the Square Kilometer Array (SKA). In this article we focus on the post-reionization signal and investigate the of cross correlating the 21 cm signal with other tracers of the large scale structure. We consider the cross-correlation of the post-reionization 21 cm signal with the Lyman-alpha forest, Lyman-break galaxies and late time anisotropies in the CMBR maps like weak lensing and the Integrated Sachs Wolfe effect. We study the feasibility of detecting the signal and explore the possibility of obtaining constraints on cosmological models using it.

Dark energy imprints on the kinematic Sunyaev–Zel'dovich signal

We investigate the imprint of dark energy on the kinetic Sunyaev–Zel'dovich (kSZ) angular power spectrum on scales of ℓ=1000 to 10000, and find that the kSZ signal is sensitive to the dark energy parameter. For example, varying the constant w by 20% around w=−1 results in a ≳10% change on the kSZ spectrum; changing the dark energy dynamics parametrized by wa by ±0.5, a 30% change on the kSZ spectrum is expected. We discuss the observational aspects and develop a fitting formula for the kSZ power spectrum. Finally, we discuss how the precise modeling of the post-reionization signal would help the constraints on patchy reionization signal, which is crucial for measuring the duration of reionization.

INTENSITY MAPPING ACROSS COSMIC TIMES WITH THE Lyα LINE

We present a quantitative model of Lyman-alpha (Ly-alpha) emission throughout cosmic history and determine the prospects for intensity mapping of spatial fluctuations in the Ly-alpha signal. Since i) our model assumes at z>6 the minimum star formation required to sustain reionization and ii) is based at z<6 on a luminosity function extrapolated from the few observed bright Ly-alpha emitters, this should be considered a lower limit. Mapping the line emission allows probes of reionization, star formation, and large-scale structure (LSS) as a function of redshift. While Ly-alpha emission during reionization has been studied, we also predict the post-reionization signal to test predictions of the intensity and motivate future intensity mapping probes of reionization. We include emission from massive dark matter halos and the intergalactic medium (IGM) in our model. We find agreement with current, measured luminosity functions of Ly-alpha emitters at z<8. However, diffuse IGM emission, not associated with Ly-alpha emitters, dominates the intensity up to z~10. While our model is applicable for deep-optical or near-infrared observers like the SuMIre survey or the James Webb Space Telescope, only intensity mapping will detect the diffuse IGM emission. We also construct a 3D power spectrum model of the Ly\alpha emission, and characterize possible foreground contamination. Finally, we study the prospects of an intensity mapper for measuring Ly-alpha fluctuations while identifying interloper contamination for removal. Our results suggest that while the reionization signal is challenging, Ly-alpha fluctuations can be an interesting new probe of LSS at late times when used in conjunction with other lines like, e.g., H-alpha, to monitor low-redshift foreground confusion.

The kinetic Sunyaev-Zel’dovich signal from inhomogeneous reionization: a parameter space study

[ABRIDGED] Inhomogeneous reionization acts as a source of arcminute-scale anisotropies in the cosmic microwave background (CMB), the most important of which is the kinetic Sunyaev-Zel'dovich (kSZ) effect. Observational efforts with the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) are poised to detect this signal for the first time. Indeed, recent SPT measurements place a bound on the dimensionless kSZ power spectrum around a multipole of l=3000 of P_tot < 2.8 (6) micro K^2 at 95% C.L., by ignoring (allowing) correlations between the thermal Sunyaev-Zel'dovich (tSZ) effect and the cosmic infrared background (CIB). To interpret these and upcoming observations, we compute the kSZ signal from a suite of ~ 100 reionization models using the publicly available code 21cmFAST. Our physically motivated reionization models are parameterized by the ionizing efficiency of high-redshift galaxies, the minimum virial temperature of halos capable of hosting stars, and the ionizing photon mean free path. We predict the contribution of patchy reionization to be P_patchy = 1.5-3.5 micro K^2. Therefore, even when conservatively adopting a low estimate of the post-reionization signal, P_OV ~ 2 micro K^2, none of our models are consistent with the aggressive 2sigma SPT bound that does not include correlations. This implies that either: (i) the early stages of reionization occurred in a much more homogeneous manner than suggested by the stellar-driven scenarios we explore, such as would be the case if, e.g., very high energy X-rays or exotic particles contributed significantly; and/or (ii) that there is a significant correlation between the CIB and the tSZ. On the other hand, the conservative SPT bound is compatible with all of our models, and is on the boarder of constraining reionization.

Evolution of the 21 cm signal throughout cosmic history

The potential use of the redshifted 21 cm line from neutral hydrogen for probing the epoch of reionization is motivating the construction of several low-frequency interferometers. There is also much interest in the possibility of constraining the initial conditions from inflation and the nature of the dark matter and dark energy by probing the power spectrum of density perturbations in three dimensions and on smaller scales than probed by the microwave background anisotropies. Theoretical understanding of the 21 cm signal has been fragmented into different regimes of physical interest. In this paper, we make the first attempt to describe the full redshift evolution of the 21 cm signal between $0&lt;z&lt;300$. We include contributions to the 21 cm signal from fluctuations in the gas density, temperature, and neutral fraction, as well as the $\mathrm{Ly}\ensuremath{\alpha}$ flux, and allow for a post-reionization signal from damped $\mathrm{Ly}\ensuremath{\alpha}$ systems. Our comprehensive analysis provides a useful foundation for optimizing the design of future arrays whose goal is to separate the particle physics from the astrophysics, either by probing the peculiar velocity distortion of the 21 cm power spectrum, or by extending the 21 cm horizon to $z\ensuremath{\gtrsim}25$ before the first galaxies had formed, or to $z\ensuremath{\lesssim}6$ when the residual pockets of hydrogen trace large-scale structure.