arXiv subjects

Zhaoting Chen

Publications and source records attributed to Zhaoting Chen.

26 records · Page 2Linked to original sources

arXiv2024

Reionization Parameter Inference from 3D Minkowski Functionals of the 21 cm Signals

The Minkowski Functionals (MFs), a set of topological summary statistics, have emerged as a powerful tool for extracting non-Gaussian information. We investigate the prospect of constraining the reionization parameters using the MFs of the 21 cm brightness temperature field from the epoch of reionization (EoR). Realistic effects, including thermal noise, synthesized beam, and foreground avoidance, are applied to the mock observations from the radio interferometric array experiments such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA). We demonstrate that the MFs of the 21 cm signal measured with SKA-Low can be used to distinguish different reionization models, whereas the MF measurement with a HERA-like array cannot be made accurately enough. We further forecast the accuracies with which the MF measurements can place constraints on reionization parameters, using the standard MCMC analysis for parameter inference based on forward modeling. We find that for SKA-Low observation, MFs provide unbiased estimations of the reionization parameters with accuracies comparable to the power spectrum (PS) analysis. Furthermore, joint constraints using both MFs and PS can improve the constraint accuracies by up to $30\%$ compared to those with the PS alone. Nevertheless, the constraint accuracies can be degraded if the EoR window is shrunk with strong foreground avoidance. Our analysis demonstrates the promise of MFs as a set of summary statistics that extract complementary information from the 21 cm EoR field to the two-point statistics, which suggests a strong motivation for incorporating the MFs into the data analysis of future 21 cm observations.

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arXiv2023

Detecting the HI Power Spectrum in the Post-Reionization Universe with SKA-Low

We present a survey strategy to detect the neutral hydrogen (HI) power spectrum at $5<z<6$ using the SKA-Low radio telescope in presence of foregrounds and instrumental effects. We simulate observations of the inherently weak HI signal post-reionization with varying levels of noise and contamination with foreground amplitudes equivalent to residuals after sky model subtraction. We find that blind signal separation methods on imaged data are required in order to recover the HI signal at large cosmological scales. Comparing different methods of foreground cleaning, we find that Gaussian Process Regression (GPR) performs better than Principle Component Analysis (PCA), with the key difference being that GPR uses smooth kernels for the total data covariance. The integration time of one field needs to be larger than $\sim 250$ h to provide large enough signal-to-noise ratio (SNR) to accurately model the data covariance for foreground cleaning. Images within the primary beam field-of-view give measurements of the HI power spectrum at scales $k\sim 0.02\,{\rm Mpc^{-1}}-0.3\,{\rm Mpc^{-1} }$ with SNR $\sim 2-5$ in $Δ[{\rm log}( k/{\rm Mpc^{-1}})] = 0.25$ bins assuming an integration time of $600$ h. Systematic effects, which introduce small-scale fluctuations across frequency channels, need to be $\lesssim 5\times 10^{-5}$ to enable unbiased measurements outside the foreground wedge. Our results provide an important validation towards using the SKA-Low array for measuring the HI power spectrum in the post-reionization Universe.

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arXiv2022

Towards Optimal Foreground Mitigation Strategies for Interferometric HI Intensity Mapping in the Low-Redshift Universe

We conduct the first case study towards developing optimal foreground mitigation strategies for neutral hydrogen (HI) intensity mapping using radio interferometers at low redshifts. A pipeline for simulation, foreground mitigation and power spectrum estimation is built, which can be used for ongoing and future surveys using MeerKAT and Square Kilometre Array Observatory (SKAO). It simulates realistic sky signals to generate visibility data given instrument and observation specifications, which is subsequently used to perform foreground mitigation and power spectrum estimation. A quadratic estimator formalism is developed to estimate the temperature power spectrum in visibility space. Using MeerKAT telescope specifications for observations in the redshift range z~0.25-0.30 corresponding to the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey, we present a case study where we compare different approaches of foreground mitigation. We find that component separation in visibility space provides a more accurate estimation of HI clustering comparing to foreground avoidance, with the uncertainties being 30 per cent smaller. Power spectrum estimation from image is found to be less robust with larger bias and more information loss when compared to estimation in visibility. We conclude that for z~0.25-0.30, the MIGHTEE survey will be capable of measuring the HI power spectrum from k~0.5 Mpc$^{-1}$ to k~10 Mpc$^{-1}$ with high accuracy. We are the first to show that, at low redshift, component separation in visibility space suppresses foreground contamination at large line-of-sight scales, allowing measurement of HI power spectrum closer to the foreground wedge, crucial for data analysis towards future detections.

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arXiv2021

TheHaloMod: An online calculator for the halo model

The halo model is a successful framework for describing the distribution of matter in the Universe -- from weak lensing observables to galaxy 2-point correlation functions. We review the basic formulation of the halo model and several of its components in the context of galaxy two-point statistics, developing a coherent framework for its application. We use this framework to motivate the presentation of a new Python tool for simple and efficient calculation of halo model quantities, and their extension to galaxy statistics via a \textit{halo occupation distribution}, called \halomod. This tool is efficient, simple to use, comprehensive and importantly provides a great deal of flexibility in terms of custom extensions. This Python tool is complemented by a new web-application at https://thehalomod.app that supports the generation of many halo model quantities directly from the browser -- useful for educators, students, theorists and observers.

astro-ph.CO↗

arXiv2021

Extracting HI Astrophysics from Interferometric Intensity Mapping

We present a new halo model of neutral hydrogen (HI) calibrated to galaxy formation simulations at redshifts $z\sim0.1$ and $z\sim1.0$ that we employ to investigate the constraining power of interferometric HI intensity mapping on HI astrophysics. We demonstrate that constraints on the small-scale HI power spectrum can break the degeneracy between the HI density $Ω_{\rm HI}$ and the HI bias $b_{\rm HI}$. For $z\sim0.1$, we forecast that an accurate measurement of $Ω_{\rm HI}$ up to 6% level precision and the large-scale HI bias $b_{\rm HI}^0$ up to 1% level precision can be achieved using Square Kilometre Array (SKA) pathfinder data from MeerKAT and Australian SKA Pathfinder (ASKAP). We also propose a new description of the HI shot noise in the halo model framework in which a scatter of the relation between the HI mass of galaxies and their host halo mass is taken into account. Furthermore, given the number density of HI galaxies above a certain HI mass threshold, future surveys will also be able to constrain the HI mass function using only the HI shot noise. This will lead to constraints at the 10% level using the standard Schechter function. This technique will potentially provide a new way of measuring the HI Mass Function, independent from existing methods. We predict that the SKA will be able to further improve the low-redshift constraints by a factor of 3, as well as pioneering measurements of HI astrophysics at higher redshifts.

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arXiv2020

New test on general relativity and $f(T)$ torsional gravity from galaxy-galaxy weak lensing surveys

We use galaxy-galaxy weak lensing data to perform a novel test on general relativity (GR) and $f(T)$ torsional gravity. In particular, we impose strong constraints using the torsional (teleparallel) formulation of gravity in which the deviation from GR is quantified by a single parameter $α$, an approximation which is always valid at low-redshift Universe and weak gravitational fields. We calculate the difference in the deflection angle and eventually derive the modified excess surface density profile, which is mainly affected at small scales. Confronting the predictions with weak lensing data from the Sloan Digital Sky Survey Data Release 7, we obtain the upper bound on the deviation parameter, which, expressed via the dimensionless percentage in the Universe energy content, reads as ${\rm{log_{10}}}Ω_α\le -18.52_{-0.42}^{+0.80}$(stat)$_{-0.37}^{+1.50}$(sys)$ [R_c/0.015R_{200}]$ with systematics mainly arising from the modelling of astrophysics, upon a reasonable choice of cut-off radius for $f(T)$ gravity in form of $T + αT^2$. To our knowledge, this is the first time that GR is verified at such an accuracy at the corresponding scales.

astro-ph.CO↗

arXiv2019

Stages of Reionization as revealed by the Minkowski Functionals

We study the evolution of the hydrogen ionization field during the epoch of reionization (EoR) using semi-numerical simulations. By calculating the Minkowski functionals (MFs) of the 21cm brightness temperature field, which provides a quantitative description of topology of the neutral and ionized regions, we find that the reionization process can be divided into five stages, each with different topological structures, corresponding to isolated ionized regions ("bubbles"); connected ionized region ("ionized fibers") which percolate through the cosmic volume; a sponge-like configuration with intertwined neutral and ionized regions after the overlap of bubbles; connected neutral regions ("neutral fibers") when the ionized region begin to surround the remaining neutral region; and isolated neutral regions ("islands"), before the whole space is ionized except for the rare dense clumps in galaxies and minihalos and the reionization process is completed. We use the MFs and the size statistics on the ionized or neutral regions to distinguish these different stages, and find the neutral fractions at which the transition of the different stages occur. At the later stages of reionization the neutral regions are more isolated than the ionized regions, this is the motivation for the island model description of reionization. We compare the late stage topological evolution in the island model and the bubble model, showing that in the island model the neutral fibers are more easily broken into multiple pieces due to the ionizing background.

astro-ph.CO↗

arXiv2019

Testing the scale-dependent hemispherical asymmetry with the 21-cm power spectrum from the epoch of reionization

Hemispherical power asymmetry has emerged as a new challenge to cosmology in early universe. While the cosmic microwave background (CMB) measurements indicated the asymmetry amplitude $A \simeq 0.07$ at the CMB scale $k_{\rm CMB}\simeq 0.0045\,{\rm Mpc}^{-1}$, the high-redshift quasar observations found no significant deviation from statistical isotropy. This conflict can be reconciled in some scale-dependent asymmetry models. We put forward a new parameterization of scale-dependent asymmetric power spectrum, inspired by a multi-speed inflation model. The 21-cm power spectrum from the epoch of reionization can be used to constrain the scale-dependent hemispherical asymmetry. We demonstrate that an optimum, multi-frequency observation by the Square Kilometre Array (SKA) Phase 2 can impose a constraint on the amplitude of the power asymmetry anomaly at the level of $ΔA \simeq 0.2$ at $0.056 \lesssim k_{\rm 21cm} \lesssim 0.15 \,{\rm Mpc}^{-1}$. This limit may be further improved by an order of magnitude as $ΔA \simeq 0.01$ with a cosmic variance limited experiment such as the Omniscope.

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