arXiv subjects

Shun Saito

Publications and source records attributed to Shun Saito.

At least 19 recordsLinked to original sources

arXiv2026

HETDEX: Star Formation Stochasticity Diagram of Lyman Alpha Emitting Galaxies at Cosmic Noon Confirms Three Archetypes

In this work, we aim to measure the star formation stochasticity of Lyman Alpha Emitting Galaxies (LAEs) at Cosmic Noon. We identify 270 LAEs from the HETDEX Survey in the COSMOS field with rest-UV-through-NIR photometry from CANDELS\null. For each LAE, we perform non-parametric gaussian-process star formation history (SFH) reconstruction using the Dense Basis method. Our HETDEX LAE sample is described well by the three SFH archetypes defined for ODIN LAEs in Firestone et al. 2025 with comparable frequency: First Burst, Dominant Burst, and Nondominant Burst. The rapidly rising Star Formation Rates (SFRs) of First Burst LAEs are not adequately represented in traditional SFR$_{100}-M_*$ diagrams, where SFR$_{100}$ is averaged over the most recent 100Myr. This motivates the usage of SFR$_{10}-M_*$, where SFR$_{10}$ is averaged over the most recent 10Myr. We introduce the Star Formation Stochasticity Diagram, a diagnostic tool that probes variations in galaxies' SFRs across cosmic time. By eliminating the confounding factor of redshift evolution, we are able to employ a gaussian mixture model to decompose our ratio of short- vs.long-term SFR into statistically motivated sub-populations. This agnostic component decomposition reveals three populations consistent with the empirical LAE SFH archetypes. We can, therefore, summarize the overall stellar mass assembly of LAEs with this ratio, even without viewing their full star formation histories.

astro-ph.GA↗

arXiv2026

HETDEX [OII] galaxies at $z \le 0.48$: Volume-limited samples and their power spectra

The catalog from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Public Data Release 1 (PDR1) contains half a million emission-line-selected [OII] galaxies spread across $540~\mathrm{deg}^2$ at $z \le 0.48$ from HETDEX's unprecedented untargeted spectroscopic survey. In this paper, we construct volume-limited samples from PDR1 in three luminosity bins across the two main fields: "Spring'' and "Fall''. The numbers of galaxies in the bins range from 11,354 to 64,794 and number densities, $\bar{n}\simeq (2-5)\times10^{-3}~h^3~\mathrm{Mpc}^{-3}$, are higher than those of typical cosmological spectroscopic surveys of emission-line galaxies by a factor of five to ten. The monopole and quadrupole power spectra derived from these samples are in excellent agreement with the mock power spectra from the Uchuu simulation based on a flat $\Lambda$CDM model and the cosmological parameters from the Planck cosmic microwave background data, at all wavenumbers used for the measurement ($0.01<k<0.7~h~\mathrm{Mpc}^{-1}$). We find that the power spectrum amplitudes are consistent with a characteristic dark matter halo mass of $\log(M_0~[h^{-1}M_{\odot}])\simeq 11.9$-$12.3$, with the halo mass showing a weak dependence on [OII] luminosity, $M_0\propto L^a$, increasing with a slope of $a = 0.37\pm0.10$. The best-fit mock suggests that approximately 13 percent of the [OII] galaxies in our sample reside in subhalos. The new, high-density tracers of the underlying matter distribution presented in this paper provide precise measurements of clustering in a low-redshift regime sensitive to the late-time growth of structures. These samples will form the basis for forthcoming analyses of the redshift-space distortion effect, galaxy-halo connection, and cross-correlations with external low-redshift probes.

astro-ph.CO↗

arXiv2026

HETDEX Public Data Release 1: Source Catalog 2 and Data Cubes from ~90 sq deg of Integral-Field Optical Spectroscopy

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is a wide-field, integral-field spectroscopic survey designed to map the large-scale distribution of Lyman-alpha emitting galaxies (LAEs) at 1.88 < z < 3.52 and constrain dark energy at cosmic noon. Using the 10-m Hobby-Eberly Telescope and the Visible Integral-Field Replicable Unit (IFU) Spectrograph, HETDEX obtains >35,000 spectra per exposure over 3500-5500 {\AA} at R~800 with ~1.8 arcsec image quality, enabling an untargeted census of emission-line galaxies across 540 sq deg. We present HETDEX Public Data Release 1 (PDR1), comprising 431,713 IFU observations covering 86.67 sq deg of noncontiguous sky in the Spring (13h, +51{\deg}) and Fall (1.5h, 0{\deg}) fields, along with legacy regions (COSMOS, GOODS-N, NEP, SA22). PDR1 includes the HETDEX Public Source Catalog 2 (HPSC2), an expanded and reprocessed version of Mentuch Cooper et al. (2023) incorporating four additional years of data, improved quality control, and new machine learning classifiers. HPSC2 contains 426,654 LAEs, 491,411 [O II] emitters, 19,457 low-z galaxies, 18,303 active galactic nuclei, and 150,608 stars, providing coordinates, redshifts or stellar velocities, and 1D spectra for each source. Because the data cubes use local sky subtraction optimized for faint emission-line detection, they are not suited for absolute surface-brightness measurements or very extended nearby galaxies. Appendix materials include the full detection catalog, the 1.6 million-candidate LAE sample, and raw detection databases. All products are publicly accessible through the HETDEX data portal (https://hetdex.org/data-results/), including access to a public JupyterLab. HPSC2 is also publicly available via Zenodo (DOI: 10.5281/zenodo.19581262).

astro-ph.GA↗

arXiv2026

No evidence for phantom crossing: local goodness-of-fit improvements do not persist under global Bayesian model comparison

Recent cosmological data have been interpreted as indicating deviations from $Λ$CDM within the standard $w_0w_a$ parametrization, including hints of phantom crossing and dynamical dark energy. However, such inferences can be parametrization-dependent and need not imply a statistically robust detection. We test these claims by comparing $Λ$CDM, $w_0w_a$, and thawing quintessence models, using the Deviance Information Criterion (DIC) and the Bayesian evidence $\ln \mathcal{Z}$. We find that $w_0w_a$ can provide a slightly improved local fit; however, this improvement is confined to a limited region of the parameter space. The global Bayesian evidence does not support it once the full prior volume is accounted for. In particular, cases with $Δ{\rm DIC}<0$ but $Δ\ln \mathcal{Z}<0$ indicate that these improvements are not statistically significant. We show that all models are statistically indistinguishable, and that there is no statistically consistent evidence across different datasets for either dynamical dark energy or phantom crossing.

astro-ph.CO↗

arXiv2026

Golden and Silver Dark Sirens for precise H0 measurement with HETDEX

Gravitational waves (GWs) from compact binary coalescences are standard sirens that provide a direct measure of the source's luminosity distance, enabling an independent measurement of the Hubble constant (H0). While a bright siren -- a GW event with an identified electromagnetic (EM) counterpart -- provided the first such constraint, most detections, currently dominated by black hole mergers, lack EM signatures. A measurement of H0 is still possible with these dark sirens by statistically associating GW events with galaxies in existing catalogs based on the sky localization. In this work, we explore the potential of two subsets of sirens: rare golden dark sirens, for which a single galaxy dominates the H0 posterior, and silver dark sirens, which are far more common but have a larger set of plausible host galaxies. Using the fifth internal data release of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), we assess the suitability of the Visible Integral-field Replicable Unit Spectrograph (VIRUS) for spectroscopic follow-up of dark sirens. VIRUS exposures of the standard HETDEX depth provide precise redshifts and exquisite completeness within z = 0.2. After a single year of observations with the upgraded LIGO-A# network, the combined sample of golden and silver dark sirens with z < 0.2 and follow-up VIRUS observations can potentially yield a few-percent constraint on H0. Our predictions suggest that spectroscopic redshift surveys such as HETDEX can play a key role in realizing high-precision cosmology with dark sirens in the near future. Standard-siren distance measurements offer a critical, fully independent path to the local value of H0 to resolve the Hubble tension.

astro-ph.CO↗

arXiv2026

Unveiling Hidden Lyman Alpha Emitters in the DESI DR1 Data

We present an automatic method based on machine-learning convolutional neural network (CNN) architecture to detect Lyman alpha emitters (LAE) hidden in the Data Release 1 spectroscopic dataset of the Dark Energy Spectroscopic Instrument (DESI). Those LAEs mostly have incorrect redshift estimations because the current DESI pipeline is not designed to detect and measure the redshifts of galaxies at $z>2$. To uncover those sources, we first visually inspect thousands of DESI spectra and construct a sample, consisting of both LAEs and non-LAEs, for training and testing the CNN-based model to (1) detect LAEs in DESI spectra and (2) determine their Ly$α$ redshifts. The final model yields $95.2\%$ purity and $95.9\%$ completeness for detecting LAEs. We apply this model to approximately $2\times10^{6}$ spectra of sources targeted as emission-line galaxies and detect 19,685 LAEs from $z\sim2$ to $3.5$ within 12 minutes with a single GPU, illustrating the high efficiency of this model for identifying LAEs. The detected LAEs are mostly at the bright end of the luminosity function with Ly$α$ luminosity $L_{\rm Lyα} \gtrsim 10^{43}$ erg/s. The high signal-to-noise composite spectrum of the detected LAEs further shows various spectral features, including P-Cygni profiles of metal lines and MgII emission lines, possible indicators of Lyman continuum escape fraction, revealing the rich astrophysical information in this LAE sample. Finally, this sample can be used to train and validate the pipelines for redshift determination of LAEs for the preparation of the DESI-II survey.

astro-ph.GA↗

arXiv2026

Enhancing Lyα Emitter Identification in HETDEX with a Convolutional Neural Network

We present a deep learning framework to enhance the identification of Ly$α$ emitters (LAEs) in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), an untargeted spectroscopic survey of LAEs at $1.9 < z < 3.5$ without imaging pre-selection. We primarily address the low signal-to-noise ratio (S/N) regime ($4.8 \leq \mathrm{S/N} \leq 5.5$), where LAE candidates suffer from substantial noise contamination. To distinguish LAE candidates from artifacts and sky residuals, we employ a convolutional neural network (CNN) trained on two-dimensional spectral images of single emission lines. The training sample is constructed from the HETDEX COSMOS catalog, with external validation from ancillary observations and our participatory science project, \textit{Dark Energy Explorers}. For small-format, low-resolution spectroscopic data, the model achieves a balanced accuracy, precision, and recall of $94.1\%$, $97.5\%$, and $97.5\%$, respectively, in the high-S/N regime ($\mathrm{S/N}>5.5$), and $85.1\%$, $78.2\%$, and $84.4\%$ in the low-S/N regime. Using HETDEX LAEs independently identified by DESI spectroscopy, the model recovers $99\%$ and $93\%$ of the high- and low-S/N LAEs, respectively. Visual attribution indicates that the CNN attends to smooth, spatially extended central emission in true positives and to irregular or noisy features in true negatives. Applied to the full HETDEX catalog, the CNN enables an S/N threshold down to 4.8 by suppressing spurious spikes across $z\sim 1.9$--$2.5$ in the redshift distribution. Our approach facilitates HETDEX cosmological analyses by mitigating false positives in galaxy clustering and highlights the value of domain-specific deep learning for refining low-S/N spectroscopic identification in untargeted surveys.

astro-ph.GA↗

arXiv2026

Lyα Intensity Mapping in HETDEX: Galaxy-Lyα Intensity Cross-Power Spectrum

We present a measurement of the Lyman-$α$ (Ly$α$) intensity mapping power spectrum from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We measure the cross-power spectrum of the Ly$α$ intensity and Ly$α$-emitting galaxies (LAEs) in a redshift range of $1.9 < z < 3.5$. We calculate the intensity from HETDEX spectra that do not contain any detected LAEs above a signal-to-noise ratio of $5.5$. To produce a power spectrum model and its covariance matrix, we simulate the data using lognormal mocks for the LAE catalog and Ly$α$ intensity in redshift space. The simulations include the HETDEX sensitivity, selection function, and mask. The measurements yield the product of the LAE bias, the intensity bias, the mean intensity of undetected sources, and the ratio of the actual and fiducial redshift-space distortion parameters, $b_\mathrm{g} b_I \langle I \rangle \bar{F}_{\rm RSD} / \bar{F}^{\rm fid}_{\rm RSD}= (6.7 \pm 3.1)$, $(11.7 \pm 1.4)$, and $(8.3 \pm 1.5) \times 10^{-22} \, \text{erg}\, \text{s}^{-1} \, \text{cm}^{-2} \, \text{arcsec}^{-2} \, \text{Å}^{-1}$ in three redshift bins centered at $\bar z=2.1$, 2.6, and 3.2, respectively. The results are reasonably consistent with cosmological hydrodynamical simulations that include Ly$α$ radiative transfer. They are, however, significantly smaller than previous results from cross-correlations of quasars with Ly$α$ intensity. These results demonstrate the statistical power of HETDEX for Ly$α$ intensity mapping and pave the way for a more comprehensive analysis. They will also be useful for constraining models of Ly$α$ emission from galaxies used in modern cosmological simulations of galaxy formation and evolution.

astro-ph.CO↗

arXiv2026

Illuminating the Physics of Cosmic Origin and Evolution: A UK Space Frontiers 2035 White Paper

Understanding the Universe's origins and evolution remains one of the most fundamental challenges in modern cosmology. This white paper explores three key science priorities in this field: unravelling the physics of cosmic inflation, investigating the accelerating expansion of the Universe, and precisely measuring the sum of the neutrino masses. Achieving these goals requires a dedicated survey to map the large-scale structure at high redshift in unprecedented detail. We describe how this can be achieved through a mission concept called SIRMOS, providing a high-throughput, highly multiplexed spectroscopic capability to obtain accurate redshifts for over 100 million galaxies over a wide sky area. Such a survey would leverage the deepest existing wide-area photometric catalogues for targeting, with spectra offering continuous 1.25-2.5~$μ$m wavelength coverage at moderate resolution, allowing precise redshift measurements in the $1<z<4$ range with minimal bias. We outline the scientific opportunities this presents. Recent years have seen significant advances in instrumentation, including digital micromirror devices, complex telescope mirrors, large detector arrays, and data processing pipelines. While these technologies have been demonstrated in terrestrial applications, such a survey is a unique opportunity to apply these proven capabilities in space to address fundamental questions in cosmology. Participation in such a mission will simultaneously deliver a compelling science case, help align UK Space Agency and STFC strategies, demonstrate the UK's growing capability in end-to-end space missions, and strengthen the national space economy through high-value industrial participation.

astro-ph.IM↗

arXiv2025

Simulating realistic Lyman-$α$ emitting galaxies including the effect of radiative transfer

We present an empirical yet physically motivated simulation of realistic Lyman-$α$ emitters (LAEs) at $z\sim2-3$, crucial for ongoing and forthcoming cosmological LAE surveys. We combine an empirical $\mathtt{UniverseMachine}$ galaxy-halo model with a simple spherical expanding shell model for the Lyman-$α$ radiative transfer, calibrating only three free parameters to simultaneously reproduce the observed Lyman-$α$ luminosity function and the angular clustering. Our LAE model is further supported by its consistency with other observables such as the Lyman-$α$ equivalent width distribution, the Lyman-$α$ escape fraction as a function of stellar mass and dust reddening, and the systemic velocity offsets. Our LAE model provides predictions for the halo occupation distributions for LAEs and relationship between Ly$α$ luminosity and halo mass, including the distribution of satellite LAEs. Our work provides a crucial first step towards creating a high-fidelity LAE synthetic catalog for the LAE cosmology surveys. We make our LAE catalog and spectra publicly available upon publication.

astro-ph.GA↗

arXiv2025

DESI Spectroscopy of HETDEX Emission-line Candidates I: Line Discrimination Validation

The Hobby-Eberly Dark Energy Experiment (HETDEX) is an untargeted spectroscopic galaxy survey that uses Ly$α$ emitting galaxies (LAEs) as tracers of 1.9 < z < 3.5 large scale structure. Most detections consist of a single emission line, whose identity is inferred via a Bayesian analysis of ancillary data. To determine the accuracy of these line identifications, HETDEX detections were observed with the Dark Energy Spectroscopic Instrument (DESI). In two DESI pointings, high confidence spectroscopic redshifts are obtained for 1157 sources, including 982 LAEs. The DESI spectra are used to evaluate the accuracy of the HETDEX object classifications, and tune the methodology to achieve the HETDEX science requirement of $\lesssim 2\%$ contamination of the LAE sample by low-redshift emission-line galaxies, while still assigning $96\%$ of the true Ly$α$ emission sample with the correct spectroscopic redshift. We compare emission line measurements between the two experiments assuming a simple Gaussian line fitting model. Fitted values for the central wavelength of the emission line, the measured line flux and line widths are consistent between the surveys within uncertainties. Derived spectroscopic redshifts, from the two classification pipelines, when both agree as an LAE classification, are consistent to within $\langle Δz / (1 + z) \rangle = 6.9\times 10^{-5}$ with an rms scatter of $3.3\times 10^{-4}$.

astro-ph.CO↗

arXiv2025

Squeezing information from radio surveys to probe the primordial Universe

A major goal of cosmology is to understand the nature of the field(s) which drove primordial Inflation. Through future observations, the statistics of large-scale structure will allow us to probe primordial non-Gaussianity of the curvature perturbation at the end of Inflation. We show how a new correlation statistic can significantly improve these constraints over conventional methods. Next-generation radio telescope arrays are under construction which will map the density field of neutral hydrogen to high redshifts. These telescopes can operate as an interferometer, able to probe small scales, or as a collection of single dishes, combining signals to map the large scales. We show how to fuse these these operating modes in order to measure the squeezed bispectrum with higher precision and greater economy. This leads to constraints on primordial non-Gaussianity that will improve on measurements by Planck, and out-perform other surveys such as Euclid. We forecast that $σ(f_{\mathrm{NL}}^{\mathrm{loc}})\sim 3$, achieved by using a small subset, $\mathcal{O}(10^2-10^3)$, of the total number of accessible triangles. The proposed method can be used for any signal that peaks in squeezed configurations.

astro-ph.CO↗

arXiv2025

Improved null tests of $Λ$CDM and FLRW in light of DESI DR2

The DESI DR2 BAO data, in combination with CMB and different SNIa datasets, exclude the flat $Λ$CDM model at more than 2.5$σ$ when analyzed through the $w_0w_a$CDM parametrization for evolving dark energy. This simple parametrization may not accurately capture the behavior of the entire redshift range at late times, which may introduce bias in the results. We use null tests that probe for deviations from flat $Λ$CDM at late times, independent of any specific dark energy parametrization. We provide several diagnostics for null tests and discuss their advantages and disadvantages. In particular, we derive diagnostics that improve on previous ones, such as the popular $O_{\rm m}$ diagnostic. The diagnostics are derived from both background and perturbed quantities. Using the combination of DESI DR2 BAO and supernova data, with or without CMB data, we find that deviations from flat $Λ$CDM are at $\sim1σ$ confidence level in most of the redshift range (more than 1$σ$ for a few small redshift intervals in a few cases). When considering SDSS BAO data instead of DESI BAO data, in combination with PantheonPlus, with or without CMB data, we find even smaller deviations. Since spatial curvature can potentially modify the results, we also test for curvature in the general $Λ$CDM model and the general FLRW model. While there is slight evidence for nonzero cosmic curvature at lower redshifts in a general $Λ$CDM model, there is no statistically significant evidence in a general FLRW model.

astro-ph.CO↗

arXiv2025

Enhancing DESI DR1 Full-Shape analyses using HOD-informed priors

We present an analysis of DESI Data Release 1 (DR1) that incorporates Halo Occupation Distribution (HOD)-informed priors into Full-Shape (FS) modeling of the power spectrum based on cosmological perturbation theory (PT). By leveraging physical insights from the galaxy-halo connection, these HOD-informed priors on nuisance parameters substantially mitigate projection effects in extended cosmological models that allow for dynamical dark energy. The resulting credible intervals now encompass the posterior maximum from the baseline analysis using gaussian priors, eliminating a significant posterior shift observed in baseline studies. In the $Λ$CDM framework, a combined DESI DR1 FS information and constraints from the DESI DR1 baryon acoustic oscillations (BAO)-including Big Bang Nucleosynthesis (BBN) constraints and a weak prior on the scalar spectral index-yields $Ω_{\rm m} = 0.2994\pm 0.0090$ and $σ_8 = 0.836^{+0.024}_{-0.027}$, representing improvements of approximately 4% and 23% over the baseline analysis, respectively. For the $w_0w_a$CDM model, our results from various data combinations are highly consistent, with all configurations converging to a region with $w_0 > -1$ and $w_a < 0$. This convergence not only suggests intriguing hints of dynamical dark energy but also underscores the robustness of our HOD-informed prior approach in delivering reliable cosmological constraints.

astro-ph.CO↗

arXiv2024

SILVERRUSH. XIV. Lya Luminosity Functions and Angular Correlation Functions from ~20,000 Lya Emitters at z~2.2-7.3 from upto 24 ${\rm deg}^2$ HSC-SSP and CHORUS Surveys: Linking the Post-Reionization Epoch to the Heart of Reionization

We present the luminosity functions (LFs) and angular correlation functions (ACFs) derived from 18,960 Ly$α$ emitters (LAEs) at $z=2.2-7.3$ over a wide survey area of $\lesssim24 {\rm deg^2}$ that are identified in the narrowband data of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) and the Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) surveys. Confirming the large sample with the 241 spectroscopically identified LAEs, we determine Ly$α$ LFs and ACFs in the brighter luminosity range down to $0.5L_{\star}$, and confirm that our measurements are consistent with previous studies but offer significantly reduced statistical uncertainties. The improved precision of our ACFs allows us to clearly detect one-halo terms at some redshifts, and provides large-scale bias measurements that indicate hosting halo masses of $\sim 10^{11} M_\odot$ over $z\simeq 2-7$. By comparing our Ly$α$ LF (ACF) measurements with reionization models, we estimate the neutral hydrogen fractions in the intergalactic medium to be $x_{\rm \HI}<0.05$ (=${0.06}^{+0.12}_{-0.03}$), $0.15^{+0.10}_{-0.08}$ (${0.21}^{+0.19}_{-0.14}$), $0.18^{+0.14}_{-0.12}$, and $0.75^{+0.09}_{-0.13}$ at $z=5.7$, $6.6$, $7.0$, and $7.3$, respectively. Our findings suggest that the neutral hydrogen fraction remains relatively low, $x_{\rm \HI} \lesssim 0.2$, at $z=5-7$, but increases sharply at $z > 7$, reaching $x_{\rm \HI} \sim 0.9$ by $z \simeq 8-9$, as indicated by recent JWST studies. The combination of our results from LAE observations with recent JWST observations suggests that the major epoch of reionization occurred around $z \sim 7-8$, likely driven by the emergence of massive sources emitting significant ionizing photons.

astro-ph.GA↗

arXiv2024

Semi-analytical model of optothermal fluidics in a confinement

In this paper, we provide the semi-analytical solution of the temperature and flow fields of a fluid confined in a narrow space between two parallel plates. The temperature increase is triggered by photothermal effects of fluids and/or boundaries due to the absorption of a focused Gaussian beam irradiated perpendicular to the fluid film, and then the temperature variation induces the flow fields through a buoyancy force and/or thermo-osmotic slip. The semi-analytical solution to this optothermal fluidic system is validated by comparing with the results of numerical simulation, and is applied to typical optothermal fluidic problems. In particular, the optothermal trap of nanoparticles observed in our previous experiment [T. Tsuji, et al., Electrophoresis, 42, 2401 (2021)] is investigated in terms of thermophoretic force and flow drag that are obtained semi-analytically. The semi-analytical solution can be shared through open-source codes that are available to researchers without the background of fluid mechanics.

physics.flu-dyn↗

arXiv2024

Lagrangian displacement field estimators in cosmology

The late-time nonlinear Lagrangian displacement field is highly correlated with the initial field, so reconstructing it could enable us to extract primordial cosmological information. Our previous work [1] carefully studied the displacement field reconstructed from the late time density field using the iterative method proposed by Ref. [2] and found that it does not fully converge to the true, underlying displacement field (e.g., $\sim 8\%$ offset at $k\sim 0.2 \ihMpc$ at $z=0.6$). We also constructed the Lagrangian perturbation theory model for the reconstructed field, but the model could not explain the discrepancy between the true and the reconstructed fields in the previous work. The main sources of the discrepancy were speculated to be a numerical artifact in the displacement estimator due to the discreteness of the sample. In this paper, we develop two new estimators of the displacement fields to reduce such numerical discreteness effect, the normalized momentum estimator~(NME) and the rescaled resumed estimator~(RRE). We show that the discrepancy Ref. [1] reported is not due to the numerical artifacts. We conclude that the method from Ref. [2] cannot fully reconstruct the shape of the nonlinear displacement field at the redshift we studied, while it is still an efficient BAO reconstruction method. In parallel, by properly accounting for the UV-sensitive term in a reconstruction procedure with an effective field theory approach, we improve the theoretical model for the reconstructed displacement field, by almost five times, from $\sim 15\%$ to the level of a few \% at $k\sim 0.2\ihMpc$ at the redshift $z=0.6$.

astro-ph.CO↗

arXiv2024

Absorption Troughs of Lyman Alpha Emitters in HETDEX

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is designed to detect and measure the redshifts of more than one million Ly$α$ emitting galaxies (LAEs) between $1.88 < z < 3.52$. In addition to its cosmological measurements, these data enable studies of Ly$α$ spectral profiles and the underlying radiative transfer. Using the roughly half a million LAEs in the HETDEX Data Release 3, we stack various subsets to obtain the typical Ly$α$ profile for the $z \sim 2-3$ epoch and to understand their physical properties. We find clear absorption wings around Ly$α$ emission, which extend $\sim 2000$ km $\mathrm{s}^{-1}$ both redward and blueward of the central line. Using far-UV spectra of nearby ($0.002 < z < 0.182$) LAEs in the CLASSY treasury and optical/near-IR spectra of $2.8 < z < 6.7$ LAEs in the MUSE-Wide survey, we observe absorption profiles in both redshift regimes. Dividing the sample by volume density shows that the troughs increase in higher density regions. This trend suggests that the depth of the absorption is dependent on the local density of objects near the LAE, a geometry that is similar to damped Lyman-$α$ systems. Simple simulations of Ly$α$ radiative transfer can produce similar troughs due to absorption of light from background sources by HI gas surrounding the LAEs.

astro-ph.GA↗