Donghui Jeong

We construct an analytical model of Population III star formation that connects the cosmological radiation background to sub-AU protostellar disk fragmentation, a dynamic range inaccessible to any single simulation. Our approach is based on combining separate models of the disparate relevant scales: from the cosmological environment to the host-halo scale, from the halo scale to the scale of the star-forming cloud, and from the cloud scale to the protostellar disk. The model agrees well with the predictions of state of the art simulations, while remaining computationally inexpensive and physically transparent. As a case study, we consider the effects of varying the Lyman-Werner flux on the Pop. III star formation efficiency. Depending on the halo properties and the strength of the dissociating radiation field, the halo-scale Pop. III star formation efficiency varies from ϵSFE, H ≈ 10−3 to ϵSFE, H ≈ 0.5. The abrupt transitions between hydrogen-deuteride cooling (in low virial temperature mini-halos subjected to low radiation backgrounds), molecular hydrogen cooling (at intermediate temperatures and radiation intensities), and atomic cooling (in higher temperature halos exposed to strong radiation fields) produces sharp features in the halo-scale star formation efficiency as a function of the halo properties. Meanwhile, at the scale of individual star-forming clouds, the star formation efficiency is ϵSFE, c ≳ 0.2. That is, pristine gas in a halo is converted into unstable clouds at a wide range of efficiencies, and these unstable clouds are efficiently converted into Pop. III stars.

The physical origin of cosmic acceleration remains one of the central questions in modern cosmology. The integrated Sachs–Wolfe (ISW) and Rees–Sciama (RS) effects, which arise from the evolution of gravitational potentials, provide a dynamical test of cosmic acceleration. We measure the cross correlation between the Planck temperature map of the cosmic microwave background (CMB) and a foreground-free map of the 100 μ m cosmic infrared background (CIB) from Y.-K. Chiang, using the k -nearest neighbor cumulative distribution function ( k NN-CDF). As the CIB map is reconstructed from ∼600 million Wide-field Infrared Survey Explorer galaxies extending to z ≈ 2.5, the measurement is equivalent to a galaxy–CMB cross correlation. We find evidence for a positive cross correlation, rejecting the null hypothesis of no correlation at p = 0.02 (2.3 σ ) using the χ ² test. We further quantify its amplitude with A _{k NN} , defined relative to an assumed cosmological model, and obtain A _{k NN} = 0.95 ± 0.20 (4.8 σ ) with respect to ΛCDM mock data including the ISW and RS effects. The k NN-CDF analysis improves the detection significance by ∼20% over the two-point correlation function. We also explore evolving dark energy by constructing two tomographic maps from the full CIB map; the results are consistent with ΛCDM. Finer tomographic reconstruction of the CIB, for example from multiband data of SPHEREx, would further tighten constraints on evolving dark energy.

We present a methodology for constructing a mock galaxy catalog for the All-sky SPECtroscopic survey of nearby galaxies (A-SPEC) using the Machine-assisted Semi-Simulation Model. The model is trained on the cosmological magnetohydrodynamical simulation IllustrisTNG to predict baryonic properties of subhalos from dark-matter-only features and is applied to our own N -body simulation tailored to satisfy the requirements of A-SPEC. We have improved the model's accuracy by introducing additional features such as subhalo anisotropy parameters and modified definitions of the subhalo environment, which result in the coefficient of determination R ² = 0.96, 0.90, 0.70, 0.79 for stellar mass, gas mass, star formation rate, and gas metallicity, respectively. The resulting mock galaxies reproduce the luminosity-dependent clustering of the target galaxies when tuned to match the number density. We discuss avenues for further improvement, including the role of environment in the predictions. We release the mock galaxy catalog with the baryonic properties predicted from the model.

The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is a wide-field, integral-field spectroscopic survey designed to map the large-scale distribution of Ly α -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 Å at R ∼ 800 with ∼ 1 . ″ 8 image quality, enabling an untargeted census of emission-line galaxies across 540 deg ² . We present HETDEX Public Data Release 1 (PDR1), comprising 431,713 IFU observations covering 86.67 deg ² of noncontiguous sky in the Spring (13 ^h , +51°) and Fall (1 . h 5, 0°) fields, along with legacy regions (Cosmic Evolution Survey, Great Observations Origins Deep Survey North, North Ecliptic Pole, SA22). PDR1 includes the HETDEX Public Source Catalog 2 (HPSC2), an expanded and reprocessed version of E. 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 ).

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 ( H ₀ ). 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 H ₀ 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 dark sirens categorized by their localization precision: ’golden’ dark sirens, defined by a sky area localization ≤0.1deg ² , and ’silver’ dark sirens, which are more common but less precisely localized (≤1deg ² ). 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 at H ₀ = 70 km s ⁻¹ Mpc ⁻¹ and follow-up VIRUS observations can potentially yield a few-percent constraint on H ₀ . 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.

We present a measurement of the 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 g b I 〈 I 〉 F ¯ RSD / F ¯ RSD fid = (6.7 ± 3.1), (11.7 ± 1.4), and (8.3 ± 1.5) × 10 ⁻²² erg s ⁻¹ cm ⁻² arcsec ⁻² Å ⁻¹ in three redshift bins centered at 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.

We present a refined deep-learning-based method to reconstruct the 3D dark matter density, gravitational potential, and peculiar velocity fields in the Zone of Avoidance (ZOA), a region near the Galactic plane with limited observational data. Using a convolutional neural network (V-Net) trained on A-SIM simulation data, our approach reconstructs density or potential fields from galaxy positions and radial peculiar velocities. The full 3D peculiar velocity field is then derived from the reconstructed potential. We validate the method with mocks that mimic the spatial distribution of the Cosmicflows-4 (CF4) catalog and apply it to actual data. Given CF4’s significant observational uncertainties and since our model does not yet account for them, we use peculiar velocities corrected via an existing Hamiltonian Monte Carlo reconstruction, rather than raw catalog distances. Our results demonstrate that the reconstructed density field recovers known galaxy clusters detected in an H i survey of the ZOA, despite this dataset not being used in the reconstruction. This agreement underscores the potential of our method to reveal structures in data-sparse regions. Most notably, streamline convergence and watershed analysis identify a mass concentration consistent with the Great Attractor, at ( l , b ) = (308 . ° 4 ± 2 . ° 4, 29 . ° 0 ± 1 . ° 9) and cz = 4960.1 ± 404.4 km s ⁻¹ , for 64% of realizations. Our method is particularly valuable as it does not rely on data point density, enabling accurate reconstruction in data-sparse regions and offering strong potential for future surveys with more extensive galaxy datasets.

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 ≲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 〈Δ z /(1 + z )〉 = 6.9 × 10 ⁻⁵ with an rms scatter of 3.3 × 10 ⁻⁴ . Data are available at https://data.desi.lbl.gov/desi/public/dr1/vac/dr1/hetdex .

We present a second-order calculation of relativistic large-scale-structure observables in cosmological perturbation theory, specifically the “cosmic rulers and clock”, which are the building-blocks of any other large-scale-structure observable, including galaxy number counts, on large scales. We calculate the scalar rulers (longitudinal perturbation and magnification) and the cosmic clock to second order, using a fully non-linear covariant definition of the observables. We validate our formulæ on three non-trivial space-time metrics: two of them are null tests on metrics which are obtained by applying a gauge transformation to the background space-time, while the third is the “separate universe” curved background, for which we can also compute the observables exactly. We then illustrate the results by evaluating the second-order observables in a simplified symmetric setup. On large scales, they are suppressed over the linear contributions by ∼10 ^-4 , while they become comparable to the linear contributions on mildly non-linear scales. The results of this paper form a significant (and the most complicated) part of the relativistic galaxy number density at second order.