arXiv subjects

Yuxiang Qin

Publications and source records attributed to Yuxiang Qin.

At least 19 recordsLinked to original sources

arXiv2026

Robust Ly$α$ forest constraints on reionization from semi-analytic galaxy formation models

The high-redshift Ly$α$ forest provides one of the most sensitive probes of the final stages of reionization, but its interpretation can depend on how the ionizing sources are modelled. We test the robustness of Ly$α$ forest-inferred reionization histories using Meraxes, a semi-analytic model of galaxy formation and reionization applied to a cosmological volume of $(210h^{-1}{\rm cMpc})^3$ with merger trees augmented down to the atomic-cooling threshold. We construct a suite of source models in which the galaxy escape fraction, $f_{\rm esc}^{\rm gal}$, is parameterized as a function of halo mass, stellar mass, star formation rate, specific star formation rate, or star-forming disc surface density. We also consider models in which accreting blackholes contribute ionizing photons, or dense circumgalactic gas further attenuates the escape of ionizing photons. Each model is calibrated to the observed distribution of Ly$α$ effective optical depths from XQR-30+. These prescriptions redistribute the escaping photon budget across halo mass and UV luminosity, introduce scatter in $f_{\rm esc}^{\rm gal}$ at fixed halo mass, and allow modest variation in the early evolution of reionization. Nevertheless, all viable calibrated models recover a late and extended EoR, with the midpoint occurring at $z\sim6.2$--6.9 and the final stages at $z\sim5.36$--5.57. Our results indicate that the late reionization history inferred from Ly$α$ forest is robust to physically motivated scatter in the galaxy--halo connection, modest AGN contributions, and phenomenological CGM attenuation.

astro-ph.CO↗

arXiv2026

Square Kilometer Array Synergies for the Epoch of Reionization and Cosmic Dawn

Synergies with other instruments will be essential in making, verifying, and interpreting a detection of the cosmic 21-cm signal from the Epoch of Reionization (EoR) and Cosmic Dawn (CD) with the Square Kilometer Array (SKA) telescope. Such synergies can (i) provide prior information about galaxies and the intergalactic medium (IGM) during the EoR/CD; (ii) pave the road to a first 21cm detection by mitigating foregrounds and systematics through cross-correlations; and (iii) give complimentary physical insights into the galaxy -- IGM connection. Here we review the current state of synergies and discuss what observations will best compliment SKA-low EoR/CD observations.

astro-ph.CO↗

arXiv2025

First Results from HERA Phase II

We report the first upper limits on the power spectrum of 21-cm fluctuations during the Epoch of Reionization and Cosmic Dawn from Phase II of the Hydrogen Epoch of Reionization Array (HERA) experiment. HERA Phase II constitutes several significant improvements in the signal chain compared to Phase I, most notably resulting in expanded frequency bandwidth, from 50-250 MHz. In these first upper limits, we investigate a small two-week subset of the available Phase II observations, with a focus on identifying new systematic characteristics of the instrument, and establishing an analysis pipeline to account for them. We report 2$σ$ upper limits in eight spectral bands, spanning $5.6 \leq z \leq 24.4$ that are consistent with thermal noise at the $2σ$ level for $k \gtrsim 0.6-0.9 h{\rm Mpc}^{-1}$ (band dependent). Our tightest limit during Cosmic Dawn ($z>12$) is $1.13\times 10^6 {\rm mK}^2$ at ($k=0.55 h{\rm Mpc}^{-1}, z=16.78$), and during the EoR ($5.5<z<12$) it is $1.78\times 10^3 {\rm mK}^2$ at ($k=0.70 h{\rm Mpc}^{-1}, z=7.05$). We find that mutual coupling has become our dominant systematic, leaking foreground power that strongly contaminates the low-$k$ modes, resulting in the loss of modes from $k=0.35-0.55$ compared to Phase I data.

astro-ph.CO↗

arXiv2025

Updated dark pixel fraction constraints on reionization's end from the Lyman-series forests of XQR-30

The fraction of "dark pixels" in the Ly$α$ and other Lyman-series forests at $z\sim 5-6$ provides a powerful constraint on the end of the reionization process. Any spectral region showing transmission must be highly ionized, while dark regions could be ionized or neutral, thus the dark pixel fraction provides a (nearly) model independent upper limit to the volume-filling fraction of the neutral intergalactic medium, modulo choices in binning scale and dark pixel definition. Here we provide updated measurements of the 3.3 comoving Mpc dark pixel fraction at $z=4.85-6.25$ in the Ly$α$, Ly$β$, and Ly$γ$ forests of 34 deep $5.8\lesssim z\lesssim 6.6$ quasar spectra from the (enlarged) XQR-30 sample. Using the negative pixel method to measure the dark pixel fraction, we derive fiducial $1σ$ upper limits on the volume-average neutral hydrogen fraction of $\langle x_{\rm{HI}}\rangle \leq \{0.030 + 0.048, 0.095 + 0.037, 0.191 + 0.056, 0.199 + 0.087\}$ at $\bar{z} = \{5.481, 5.654, 5.831, 6.043\}$ from the optimally sensitive combination of the Ly$β$ and Ly$γ$ forests. We further demonstrate an alternative method that treats the forest flux as a mixture of dark and transparent regions, where the latter are modeled using a physically-motivated parametric form for the intrinsic opacity distribution. The resulting model-dependent upper limits on $\langle x_{\rm{HI}}\rangle$ are similar to those derived from our fiducial model-independent analysis. We confirm that the bulk of reionization must be finished at $z>6$, while leaving room for an extended "soft landing" to the reionization history down to $z\sim 5.4$ suggested by Ly$α$ forest opacity fluctuations.

astro-ph.CO↗

arXiv2025

The clustering of C IV and Si IV at the end of reionisation: A perspective from the E-XQR-30 survey

We aim to study the clustering of metal absorption lines and the structures that they arise in as a function of cosmic time. We focus on C IV and Si IV absorption features that are identified along a given quasar sightline. We exploit the two-point correlation function (2PCF) to investigate the clustering of these structures as a function of their separation. We utilise the E-XQR-30 data to perform a novel analysis at z>5. We also draw on literature surveys (including XQ-100) of lower redshift quasars to investigate the possible evolution of this clustering towards cosmic noon (i.e., z~2-3). We find no significant evolution with redshift when considering the separation of absorbers in velocity space. Since we are comparing data across a large interval of cosmic time, we also consider the separation between absorbers in the reference frame of physical distances. In this reference frame, we find that the amplitude of the clustering increases with cosmic time for both C IV and Si IV on the scales of <1500 physical kpc. For the first time, we assess the 2PCF of C IV and Si IV close to the epoch of reionisation utilising the absorber catalogue from the E-XQR-30 survey. We compare this with lower redshift data and find that, on small scales, the clustering of these structures grows with cosmic time. We compare these results to the clustering of galaxies in the GAEA simulations. It appears that the structures traced by C IV are broadly comparable to the galaxies from the considered simulations. The clustering is most similar to that of the galaxies with virial masses M~10^10.5 M_sun. We require tailor-made simulations to investigate the full range of factors contributing to the observed clustering. Future ground-based spectrographs will further facilitate surveys of absorbers at this epoch with increased sensitivity.

astro-ph.GA↗

arXiv2025

A demonstration of the effect of fringe-rate filtering in the Hydrogen Epoch of Reionization Array delay power spectrum pipeline

Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different timescales. These can be isolated by designing appropriate Fourier filters that operate in fringe-rate (FR) space, the Fourier pair of local sidereal time (LST). Applications of FR filtering include separating effects that are correlated with the rotating sky vs. those relative to the ground, down-weighting emission in the primary beam sidelobes, and suppressing noise. FR filtering causes the noise contributions to the visibility data to become correlated in time however, making interpretation of subsequent averaging and error estimation steps more subtle. In this paper, we describe fringe rate filters that are implemented using discrete prolate spheroidal sequences, and designed for two different purposes -- beam sidelobe/horizon suppression (the `mainlobe' filter), and ground-locked systematics removal (the `notch' filter). We apply these to simulated data, and study how their properties affect visibilities and power spectra generated from the simulations. Included is an introduction to fringe-rate filtering and a demonstration of fringe-rate filters applied to simple situations to aid understanding.

astro-ph.CO↗

arXiv2025

On the Use of WGANs for Super-Resolution in Dark-Matter Simulations

Super-resolution techniques have the potential to reduce the computational cost of cosmological and astrophysical simulations. This can be achieved by enabling traditional simulation methods to run at lower resolution and then efficiently computing high-resolution data corresponding to the simulated low-resolution data. In this work, we investigate the application of a Wasserstein Generative Adversarial Network (WGAN) model, previously proposed in the literature, to increase the particle resolution of dark-matter-only simulations. We reproduce prior results, showing the WGAN model successfully generates high-resolution data with summary statistics, including the power spectrum and halo mass function, that closely match those of true high-resolution simulations. However, we also identify a limitation of the WGAN model in the form of smeared features in generated high-resolution data, particularly in the shapes of dark-matter halos and filaments. This limitation points to a potential weakness of the proposed WGAN-based super-resolution method in capturing the detailed structure of halos, and underscores the need for further development in applying such models to cosmological data.

astro-ph.GA↗

arXiv2025

Semi-analytic modelling of Pop. III star formation and metallicity evolution -- II. Impact on 21cm power spectrum

Simulating Population (Pop.) III star formation in mini-halos in a large cosmological simulation is an extremely challenging task but it is crucial to estimate its impact on the 21cm power spectrum. In this work, we develop a framework within the semi-analytical code meraxes to estimate the radiative backgrounds from Pop. III stars needed for the computation of the 21cm signal. We computed the 21cm global signal and power spectrum for different Pop. III models varying star formation efficiency, initial mass function (IMF) and specific X-ray luminosity per unit of star formation (LX/SFR). In all the models considered, we find Pop. III stars have little to no impact on the reionization history but significantly affect the thermal state of the intergalactic medium (IGM) due to the strong injection of X-ray photons from their remnants that heat the neutral IGM at $z \geq$ 15. This is reflected not only on the 21cm sky-averaged global signal during the Cosmic Dawn but also on the 21cm power spectrum at $z \leq$ 10 where models with strong Pop. III X-ray emission have larger power than models with no or mild Pop. III X-ray emission. We estimate observational uncertainties on the power spectrum using 21cmsense and find that models where Pop. III stars have a stronger X-ray emission than Pop. II are distinguishable from models with no or mild Pop. III X-ray emission with 1000 hours observations of the upcoming SKA1-low.

astro-ph.CO↗

arXiv2025

matvis: A matrix-based visibility simulator for fast forward modelling of many-element 21 cm arrays

Detection of the faint 21 cm line emission from the Cosmic Dawn and Epoch of Reionisation will require not only exquisite control over instrumental calibration and systematics to achieve the necessary dynamic range of observations but also validation of analysis techniques to demonstrate their statistical properties and signal loss characteristics. A key ingredient in achieving this is the ability to perform high-fidelity simulations of the kinds of data that are produced by the large, many-element, radio interferometric arrays that have been purpose-built for these studies. The large scale of these arrays presents a computational challenge, as one must simulate a detailed sky and instrumental model across many hundreds of frequency channels, thousands of time samples, and tens of thousands of baselines for arrays with hundreds of antennas. In this paper, we present a fast matrix-based method for simulating radio interferometric measurements (visibilities) at the necessary scale. We achieve this through judicious use of primary beam interpolation, fast approximations for coordinate transforms, and a vectorised outer product to expand per-antenna quantities to per-baseline visibilities, coupled with standard parallelisation techniques. We validate the results of this method, implemented in the publicly-available matvis code, against a high-precision reference simulator, and explore its computational scaling on a variety of problems.

astro-ph.IM↗

arXiv2024

Impacts and Statistical Mitigation of Missing Data on the 21cm Power Spectrum: A Case Study with the Hydrogen Epoch of Reionization Array

The precise characterization and mitigation of systematic effects is one of the biggest roadblocks impeding the detection of the fluctuations of cosmological 21cm signals. Missing data in radio cosmological experiments, often due to radio frequency interference (RFI), poses a particular challenge to power spectrum analysis as it could lead to the ringing of bright foreground modes in Fourier space, heavily contaminating the cosmological signals. Here we show that the problem of missing data becomes even more arduous in the presence of systematic effects. Using a realistic numerical simulation, we demonstrate that partially flagged data combined with systematic effects can introduce significant foreground ringing. We show that such an effect can be mitigated through inpainting the missing data. We present a rigorous statistical framework that incorporates the process of inpainting missing data into a quadratic estimator of the 21cm power spectrum. Under this framework, the uncertainties associated with our inpainting method and its impact on power spectrum statistics can be understood. These results are applied to the latest Phase II observations taken by the Hydrogen Epoch of Reionization Array, forming a crucial component in power spectrum analyses as we move toward detecting 21cm signals in the ever more noisy RFI environment.

astro-ph.CO↗

arXiv2024

Percent-level timing of reionization: self-consistent, implicit-likelihood inference from XQR-30+ Ly$α$ forest data

The Lyman alpha (Lya) forest in the spectra of z>5 quasars provides a powerful probe of the late stages of the Epoch of Reionization (EoR). With the recent advent of exquisite datasets such as XQR-30, many models have struggled to reproduce the observed large-scale fluctuations in the Lya opacity. Here we introduce a Bayesian analysis framework that forward-models large-scale lightcones of IGM properties, and accounts for unresolved sub-structure in the Lya opacity by calibrating to higher-resolution hydrodynamic simulations. Our models directly connect physically-intuitive galaxy properties with the corresponding IGM evolution, without having to tune "effective" parameters or calibrate out the mean transmission. The forest data, in combination with UV luminosity functions and the CMB optical depth, are able to constrain global IGM properties at percent level precision in our fiducial model. Unlike many other works, we recover the forest observations without evoking a rapid drop in the ionizing emissivity from z~7 to 5.5, which we attribute to our sub-grid model for recombinations. In this fiducial model, reionization ends at $z=5.44\pm0.02$ and the EoR mid-point is at $z=7.7\pm0.1$. The ionizing escape fraction increases towards faint galaxies, showing a mild redshift evolution at fixed UV magnitude, Muv. Half of the ionizing photons are provided by galaxies fainter than Muv~-12, well below direct detection limits of optical/NIR instruments including JWST. We also show results from an alternative galaxy model that does not allow for a redshift evolution in the ionizing escape fraction. Despite being decisively disfavored by the Bayesian evidence, the posterior of this model is in qualitative agreement with that from our fiducial model. We caution however that our conclusions regarding the early stages of the EoR and which sources reionized the Universe are more model-dependent.

astro-ph.CO↗

arXiv2024

The EDGES measurement disfavors an excess radio background during the cosmic dawn

In 2018 the EDGES experiment claimed the first detection of the global cosmic 21cm signal, which featured an absorption trough centered around $z \sim 17$ with a depth of approximately -500mK. This amplitude is deeper than the standard prediction (in which the radio background is determined by the cosmic microwave background) by a factor of two and potentially hints at the existence of a radio background excess. While this result was obtained by fitting the data with a phenomenological flattened-Gaussian shape for the cosmological signal, here we develop a physical model for the inhomogeneous radio background sourced by the first galaxies hosting population III stars. Star formation in these galaxies is quenched at lower redshifts due to various feedback mechanisms, so they serve as a natural candidate for the excess radio background hinted by EDGES, without violating present day measurements by ARCADE2. We forward-model the EDGES sky temperature data, jointly sampling our physical model for the cosmic signal, a foreground model, and residual calibration errors. We compare the Bayesian evidences obtained by varying the complexity and prior ranges for the systematics. We find that the data is best explained by a model with seven log-polynomial foreground terms, and that it requires calibration residuals. Interestingly, the presence of a cosmic 21cm signal with a non-standard depth is decisively disfavored. This is contrary to previous EDGES analysis in the context of extra radio background models, serving as a caution against using a ''pseudo-likelihood'' built on a model (flattened Gaussian) that is different from the one being used for inference. We make our simulation code and associated emulator publicly-available.

astro-ph.CO↗

arXiv2024

Inferring reionization and galaxy properties from the patchy kinetic Sunyaev-Zel'dovich signal

The patchy kinetic Sunyaev-Zel'dovich (kSZ) signal is an integral probe of the timing and morphology of the epoch of reionization (EoR). Recent observations have claimed a low signal-to-noise (S/N) measurement, with a dramatic increase in S/N expected in the near future. In this work, we quantify what we can learn about the EoR from the kSZ signal. We perform Bayesian inference by sampling galaxy properties and using forward-models of the kSZ as well as other EoR and galaxy observations in the likelihood. Including the recent kSZ measurement obtained by the South Pole Telescope ($\mathcal{D}_{3000}^{\rm{pkSZ}} = 1.1_{-0.7}^{+1.1} μ$K$^2$) shifts the posterior distribution in favor of faster and later reionization models, resulting in lower values of the optical depth to the CMB: $τ_e = 0.052_{-0.008}^{+0.009}$ with a 68$\%$ confidence interval (C.I.). The combined EoR and UV luminosity function observations also imply a typical ionizing escape fraction of $0.04_{-0.03}^{+0.05}$ (95$\%$ C.I.), without a strong dependence on halo mass. We show how the patchy kSZ power from our posterior depends on the commonly-used parameters of reionization. For a given midpoint and duration, the EoR morphology only has a few percent impact on the patchy kSZ power in our posterior. However, a physical model is needed to obtain tight constraints from the current low S/N patchy kSZ measurement, as it allows us to take advantage of complimentary high-$z$ observations. Future high S/N detections of the patchy kSZ should decrease the current uncertainties on the timing of the EoR by factors of $\sim$2 - 3.

astro-ph.CO↗

arXiv2024

Mapping reionization bubbles in the JWST era I: empirical edge detection with Lyman alpha emission from galaxies

Ionized bubble sizes during reionization trace physical properties of the first galaxies. JWST's ability to spectroscopically confirm and measure Lyman-alpha (Ly$α$) emission in sub-L* galaxies opens the door to mapping ionized bubbles in 3D. However, existing Lya-based bubble measurement strategies rely on constraints from single galaxies, which are limited by the large variability in intrinsic Ly$α$ emission. As a first step, we present two bubble size estimation methods using Lya spectroscopy of ensembles of galaxies, enabling us to map ionized structures and marginalize over Ly$α$ emission variability. We test our methods using Gpc-scale reionization simulations of the intergalactic medium (IGM). To map bubbles in the plane of the sky, we develop an edge detection method based on the asymmetry of Ly$α$ transmission as a function of spatial position. To map bubbles along the line-of-sight, we develop an algorithm using the tight relation between Ly$α$ transmission and the line-of-sight distance from galaxies to the nearest neutral IGM patch. Both methods can robustly recover bubbles with radius $\gtrsim$10 comoving Mpc, sufficient for mapping bubbles even in the early phases of reionization, when the IGM is $\sim70-90\%$ neutral. These methods require $\gtrsim$0.002-0.004 galaxies/cMpc$^3$, a $5σ$ Ly$α$ equivalent width upper limit of $\lesssim$30Å for the faintest targets, and redshift precision $Δz \lesssim 0.015$, feasible with JWST spectroscopy. Shallower observations will provide robust lower limits on bubble sizes. Additional constraints on IGM transmission from Ly$α$ escape fractions and line profiles will further refine these methods, paving the way to our first direct understanding of ionized bubble growth.

astro-ph.GA↗

arXiv2024

Accelerated Formation of Ultra-Massive Galaxies in the First Billion Years

Recent JWST observations have revealed an unexpected abundance of massive galaxy candidates in the early Universe, extending further in redshift and to lower luminosity than what had previously been found by sub-millimeter surveys. These JWST candidates have been interpreted as challenging the $Λ$CDM cosmology, but, so far, they have mostly relied only on rest-frame ultraviolet data and lacked spectroscopic confirmation of their redshifts. Here we report a systematic study of 36 massive dust-obscured galaxies with spectroscopic redshifts between $z_{\rm spec}=5-9$ from the JWST FRESCO survey. We find no tension with the $Λ$CDM model in our sample. However, three ultra-massive galaxies (log$M_{\star}/M_{\odot}$ $\gtrsim11.0$) require an exceptional fraction of 50% of baryons converted into stars -- two to three times higher than even the most efficient galaxies at later epochs. The contribution from an active nucleus is unlikely because of their extended emission. Ultra-massive galaxies account for as much as 17% of the total cosmic star formation rate density at $z\sim5-6$.

astro-ph.GA↗

arXiv2024

21cm signal sensitivity to dark matter decay

The redshifted 21cm signal from the Cosmic Dawn is expected to provide unprecedented insights into early Universe astrophysics and cosmology. Here we explore how dark matter can heat the intergalactic medium before the first galaxies, leaving a distinctive imprint in the 21cm power spectrum. We provide the first dedicated Fisher matrix forecasts on the sensitivity of the Hydrogen Epoch of Reionization Array (HERA) telescope to dark matter decays. We show that with 1000 hours of observation, HERA has the potential to improve current cosmological constraints on the dark matter decay lifetime by up to three orders of magnitude. Even in extreme scenarios with strong X-ray emission from early-forming, metal-free galaxies, the bounds on the decay lifetime would be improved by up to two orders of magnitude. Overall, HERA shall improve on existing limits for dark matter masses below $2$ GeV$/c^2$ for decays into $e^+e^-$ and below few MeV$/c^2$ for decays into photons.

astro-ph.CO↗

arXiv2024

Reionization morphology and intrinsic velocity offsets allow transmission of Lyman-α emission from JADES-GS-z13-1-LA

We investigate the detectability of Lyman-$α$ (Ly$α$) emission from galaxies at the onset of cosmic reionization, aiming to understand the conditions necessary for detecting high-redshift sources like JADES-GS-z13-1-LA at $z=13$. By integrating galaxy formation models with detailed intergalactic medium (IGM) reionization simulations, we construct high-redshift galaxy catalogs to model intrinsic Ly$α$ profiles and assess their transmission through the IGM. For a galaxy with $M_{\rm UV}\sim -18.5$ like JADES-GS-z13-1-LA, our fiducial model predicts a Ly$α$ transmission of ${\sim}13$% and there is a probability of observing Ly$α$ emission with an equivalent width >40A of up to 10%. We also explore how variations in the UV ionizing escape fraction, dependent on host halo mass, impact Ly$α$ detectability. Our findings reveal that reionization morphology significantly influences detection chances -- models where reionization is driven by low-mass galaxies can boost the detection probability to as much as 12%, while those driven by massive galaxies tend to reduce ionized regions around faint emitters, limiting their detectability. This study underscores the importance of reionization morphology in interpreting high-redshift Ly$α$ observations.

astro-ph.CO↗

arXiv2024

21cmEMU: an emulator of 21cmFAST summary observables

Recent years have witnessed rapid progress in observations of the Epoch of Reionization (EoR). These have enabled high-dimensional inference of galaxy and intergalactic medium (IGM) properties during the first billion years of our Universe. However, even using efficient, semi-numerical simulations, traditional inference approaches that compute 3D lightcones on-the-fly can take $10^5$ core hours. Here we present 21cmEMU: an emulator of several summary observables from the popular 21cmFAST simulation code. 21cmEMU takes as input nine parameters characterizing EoR galaxies, and outputs the following summary statistics: (i) the IGM mean neutral fraction; (ii) the 21-cm power spectrum; (iii) the mean 21-cm spin temperature; (iv) the sky-averaged (global) 21-cm signal; (v) the ultraviolet (UV) luminosity functions (LFs); and (vi) the Thomson scattering optical depth to the cosmic microwave background (CMB). All observables are predicted with sub-percent median accuracy, with a reduction of the computational cost by a factor of over 10$^4$. After validating inference results, we showcase a few applications, including: (i) quantifying the relative constraining power of different observational datasets; (ii) seeing how recent claims of a late EoR impact previous inferences; and (iii) forecasting upcoming constraints from the sixth observing season of the Hydrogen Epoch of Reionization Array (HERA) telescope. 21cmEMU is publicly-available, and is included as an alternative simulator in the public 21CMMC sampler.

astro-ph.CO↗