ChangHoon Hahn
A5060984452- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Cosmology and Gravitation Theories
- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- CCD and CMOS Imaging Sensors
- Gaussian Processes and Bayesian Inference
- Scientific Research and Discoveries
- Adaptive optics and wavefront sensing
- Music Technology and Sound Studies
- Astronomical Observations and Instrumentation
- Blind Source Separation Techniques
- Advanced Statistical Methods and Models
- Computational Physics and Python Applications
- Remote Sensing in Agriculture
- Particle physics theoretical and experimental studies
- Dark Matter and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Neutrino Physics Research
- Spectroscopy and Chemometric Analyses
- demographic modeling and climate adaptation
- Data Visualization and Analytics
- Neural Networks and Applications
- Advanced Image Processing Techniques
Princeton University
2021-2024
Lawrence Berkeley National Laboratory
2019-2024
University of California, Berkeley
2019-2023
The Ohio State University
2022
New York University
2014-2019
Flatiron Institute
2019
Flatiron Health (United States)
2019
Abstract Over the next 5 yr, Dark Energy Spectroscopic Instrument (DESI) will use 10 spectrographs with 5000 fibers on 4 m Mayall Telescope at Kitt Peak National Observatory to conduct first Stage IV dark energy galaxy survey. At z < 0.6, DESI Bright Galaxy Survey (BGS) produce most detailed map of universe during dark-energy-dominated epoch redshifts >10 million galaxies spanning 14,000 deg 2 . In this work, we present and validate final BGS target selection survey design. From Legacy...
In 2021 May, the Dark Energy Spectroscopic Instrument (DESI) began a 5 yr survey of approximately 50 million total extragalactic and Galactic targets. The primary DESI dark-time targets are emission line galaxies (ELGs), luminous red (LRGs) quasars (QSOs). bright time, will focus on two surveys known as Bright Galaxy Survey (BGS) Milky Way (MWS). also observes selection "secondary" for bespoke science goals. This paper gives an overview publicly available pipeline (desitarget) used to...
Abstract We present the measurement of Baryon Acoustic Oscillations (BAO) from Lyman- α (Ly ) forest high-redshift quasars with first-year dataset Dark Energy Spectroscopic Instrument (DESI). Our analysis uses over 420 000 Ly spectra and their correlation spatial distribution more than 700 quasars. An essential facet this work is development a new methodology on blinded dataset. conducted rigorous tests using synthetic data to ensure reliability our findings before unblinding. Additionally,...
Abstract The Dark Energy Spectroscopic Instrument (DESI) survey is a spectroscopic of tens millions galaxies at 0 < z 3.5 covering 14,000 sq. deg. the sky. In its first 1.1 yr operations, it has observed more than 14 million and 4 stars. We describe processes that govern DESI’s observations 15,000 fields composing survey. This includes planning each night’s in afternoon; automatic selection to observe during night; real-time assessment field completeness on basis observing conditions...
We present the DESI 2024 galaxy and quasar baryon acoustic oscillations (BAO) measurements using over 5.7 million unique redshifts in range 0.1<z<2.1. Divided by tracer type, we utilize 300,017 galaxies from magnitude-limited Bright Galaxy Survey with 0.1<z<0.4, 2,138,600 Luminous Red Galaxies 0.4<z<1.1, 2,432,022 Emission Line 0.8<z<1.6, 856,652 quasars 0.8<z<2.1, a ~7,500 square degree footprint. The analysis was blinded at catalog-level to avoid confirmation bias. All fiducial choices of...
Abstract The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect DESI spectra approximately 2500 bright galaxies, 3500 luminous red (LRGs), 10,000 emission-line (ELGs) obtain robust redshift identifications. We then utilize inspected information characterize performance operation. Based on visual inspection (VI) catalogs, our...
Abstract In anticipation of forthcoming data releases current and future spectroscopic surveys, we present the validation tests analysis systematic effects within velocileptors modeling pipeline when fitting mock from AbacusSummit N-body simulations. We compare constraints obtained parameter compression methods to direct (Full-Modeling) approaches galaxy power spectra, show that ShapeFit extension traditional template method is consistent with Full-Modeling standard ΛCDM space. dependence on...
Abstract We present the technical details on how large-scale structure (LSS) catalogs are constructed from redshifts measured spectra observed by Dark Energy Spectroscopic Instrument (DESI). The LSS provide information needed to determine relative number density of DESI tracers as a function redshift and celestial coordinates and, e.g., clustering statistics. produce that weighted subsamples data, each matched `random' catalog forms an unclustered sampling probability could have those data...
Abstract Baryon acoustic oscillations (BAO) provide a robust standard ruler to measure the expansion history of Universe through galaxy clustering. Density-field reconstruction is now widely adopted procedure for increasing precision and accuracy BAO detection. With goal finding optimal settings be used in DESI 2024 analysis, we assess sensitivity post-reconstruction constraints different choices our analysis configuration, performing tests on blinded data from first year observations (DR1),...
Abstract The Dark Energy Spectroscopic Instrument (DESI) will provide precise measurements of Baryon Acoustic Oscillations (BAO) to constrain the expansion history Universe and set stringent constraints on dark energy. Therefore, control global error budget due various systematic effects is required for DESI 2024 BAO analysis. In this work, we estimate level systematics induced in analysis assumed Halo Occupation Distribution (HOD) model Emission Line Galaxy (ELG) tracer. We make use mock...
Abstract In this paper, we present the estimation of systematics related to halo occupation distribution (HOD) modeling in baryon acoustic oscillations (BAO) distance measurement Dark Energy Spectroscopic Instrument (DESI) 2024 analysis. This paper focuses on study HOD for luminous red galaxies (LRG). We consider three different models LRGs, including base 5-parameter vanilla model and two extensions it, that refer as baseline extended models. The is described by 5 parameters, an...
Abstract In preparation for the next generation of galaxy redshift surveys, and in particular year-one data release from Dark Energy Spectroscopic Instrument (DESI), we investigate consistency a variety effective field theory models that describe galaxy-galaxy power spectra space into quasi-linear regime using 1-loop perturbation theory. These are employed pipelines velocileptors , PyBird Folps ν . While these have been validated independently, detailed comparison with consistent choices has...
Abstract Baryon Acoustic Oscillations can be measured with sub-percent precision above redshift two the Lyman- α (Ly ) forest auto-correlation and its cross-correlation quasar positions. This is one of key goals Dark Energy Spectroscopic Instrument (DESI) which started main survey in May 2021. We present this paper a study contaminants to Ly are mainly caused by correlated signals introduced spectroscopic data processing pipeline as well astrophysical due foreground absorption intergalactic...
Abstract We present an in-depth analysis of the fiber assignment incompleteness in Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1). This is caused by restricted mobility robotic positioner DESI focal plane, which limits number galaxies that can be observed at same time, especially small angular separations. As a result, clustering amplitude suppressed scale-dependent manner, which, if not addressed, severely impact inference cosmological parameters. discuss methods adopted...
Abstract In the era of precision cosmology, ensuring integrity data analysis through blinding techniques is paramount — a challenge particularly relevant for Dark Energy Spectroscopic Instrument (DESI). DESI represents monumental effort to map cosmic web, with goal measure redshifts tens millions galaxies and quasars. Given volume impact findings, potential confirmation bias poses significant challenge. To address this, we implement validate comprehensive blind strategy Data Release 1 (DR1),...
Abstract The Dark Energy Spectroscopic Instrument (DESI) cosmology survey includes a Bright Galaxy Survey (BGS), which will yield spectra for over 10 million bright galaxies ( r < 20.2 AB mag). resulting sample be valuable both cosmological and astrophysical studies. However, the star/galaxy separation criterion implemented in nominal BGS target selection algorithm excludes quasar host addition to bona fide stars. While this excluded population is comparatively rare (∼3–4 per square...
Abstract We present the DESI 2024 galaxy and quasar baryon acoustic oscillations (BAO) measurements using over 5.7 million unique redshifts in range 0.1 < z 2.1. Divided by tracer type, we utilize 300,017 galaxies from magnitude-limited Bright Galaxy Survey with 0.4, 2,138,600 Luminous Red Galaxies 0.4 1.1, 2,432,022 Emission Line 0.8 1.6, 856,652 quasars 2.1, a ∼ 7,500 square degree footprint. The analysis was blinded at catalog-level to avoid confirmation bias. All fiducial choices of...
Massive neutrinos suppress the growth of structure below their free-streaming scale and leave an imprint on large-scale structure. Measuring this allows us to constrain sum neutrino masses, Mν, a key parameter in particle physics beyond Standard Model. However, degeneracies among cosmological parameters, especially between Mν σ8, limit constraining power standard two-point clustering statistics. In work, we investigate whether can break these with next higher-order correlation function—the...
Abstract Massive neutrinos suppress the growth of structure on small scales and leave an imprint large-scale that can be measured to constrain their total mass, M ν . With standard analyses two-point clustering statistics, constraints are severely limited by parameter degeneracies. Ref. [1] demonstrated bispectrum, next higher-order statistic, break these degeneracies dramatically improve other cosmological parameters. In this paper, we present constraining power redshift-space galaxy...
Abstract The One-Percent survey of the Dark Energy Spectroscopic Instrument collected ∼ 270 k emission line galaxies (ELGs) at 0.8 < z 1.6. high completeness sample allowed clustering to be measured down scales never probed before, 0.04 Mpc/ h in r p for projected 2-point correlation function (2PCF) and 0.17 galaxy pair separation s 2PCF monopole quadrupole. most striking feature measurements is a strong signal smallest scales, below 0.2 1 . We analyse these data halo occupation...
Marked power spectra are two-point statistics of a marked field obtained by weighting each location with function that depends on the local density around point. We consider galaxy in redshift space up-weight low regions, and perform Fisher matrix analysis to assess information content this type using Molino mock catalogs built upon Quijote simulations. identify four different ways field, compare contained their one standard spectrum, when considering monopole quadrupole statistic. Our...
Abstract Simulation-Based Inference of Galaxies ( SimBIG ) is a forward modeling framework for analyzing galaxy clustering using simulation-based inference. In this work, we present the model, which designed to match observed SDSS-III BOSS CMASS sample. The model based on high-resolution Quijote N -body simulations and flexible halo occupation model. It includes full survey realism models observational systematics such as angular masking fiber collisions. We “mock challenge” validating...
Abstract The 3D geometries of high-redshift galaxies remain poorly understood. We build a differentiable Bayesian model and use Hamiltonian Monte Carlo to efficiently robustly infer the shapes star-forming in James Webb Space Telescope Cosmic Evolution Early Release Science observations with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mo>*</mml:mo> </mml:msub> <mml:mo...
We present the cosmological constraints from analyzing higher-order galaxy clustering on small nonlinear scales. use SimBIG, a forward modeling framework for analyses that employs simulation-based inference to perform highly efficient using normalizing flows. It leverages predictive power of high-fidelity simulations and robustly extracts information regimes inaccessible with current standard analyses. In this work, we apply SimBIG subset BOSS sample analyze redshift-space bispectrum...