ORCID Profile
0000-0003-1197-0902
Current Organisation
Princeton University
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Publisher: American Astronomical Society
Date: 26-06-2020
Publisher: IOP Publishing
Date: 10-2023
Publisher: American Astronomical Society
Date: 26-05-2023
Abstract: Over the next 5 yr, the Dark Energy Spectroscopic Instrument (DESI) will use 10 spectrographs with 5000 fibers on the 4 m Mayall Telescope at Kitt Peak National Observatory to conduct the first Stage IV dark energy galaxy survey. At z 0.6, the DESI Bright Galaxy Survey (BGS) will produce the most detailed map of the universe during the dark-energy-dominated epoch with redshifts of million galaxies spanning 14,000 deg 2 . In this work, we present and validate the final BGS target selection and survey design. From the Legacy Surveys, BGS will target an r 19.5 mag limited s le (BGS Bright), a fainter 19.5 r 20.175 color-selected s le (BGS Faint), and a smaller low- z quasar s le. BGS will observe these targets using exposure times scaled to achieve homogeneous completeness and cover the footprint three times. We use observations from the Survey Validation programs conducted prior to the main survey along with simulations to show that BGS can complete its strategy and make optimal use of “bright” time. BGS targets have stellar contamination %, and their densities do not depend strongly on imaging properties. BGS Bright will achieve % fiber assignment efficiency. Finally, BGS Bright and BGS Faint will achieve % redshift success over any observing condition. BGS meets the requirements for an extensive range of scientific applications. BGS will yield the most precise baryon acoustic oscillation and redshift-space distortion measurements at z 0.4. It presents opportunities for new methods that require highly complete and dense s les (e.g., N -point statistics, multitracers). BGS further provides a powerful tool to study galaxy populations and the relations between galaxies and dark matter.
Publisher: American Astronomical Society
Date: 20-10-2022
Abstract: The Dark Energy Spectroscopic Instrument (DESI) embarked on an ambitious 5 yr survey in 2021 May to explore the nature of dark energy with spectroscopic measurements of 40 million galaxies and quasars. DESI will determine precise redshifts and employ the baryon acoustic oscillation method to measure distances from the nearby universe to beyond redshift z 3.5, and employ redshift space distortions to measure the growth of structure and probe potential modifications to general relativity. We describe the significant instrumentation we developed to conduct the DESI survey. This includes: a wide-field, 3.°2 diameter prime-focus corrector a focal plane system with 5020 fiber positioners on the 0.812 m diameter, aspheric focal surface 10 continuous, high-efficiency fiber cable bundles that connect the focal plane to the spectrographs and 10 identical spectrographs. Each spectrograph employs a pair of dichroics to split the light into three channels that together record the light from 360–980 nm with a spectral resolution that ranges from 2000–5000. We describe the science requirements, their connection to the technical requirements, the management of the project, and interfaces between subsystems. DESI was installed at the 4 m Mayall Telescope at Kitt Peak National Observatory and has achieved all of its performance goals. Some performance highlights include an rms positioner accuracy of better than 0.″1 and a median signal-to-noise ratio of 7 of the [O ii ] doublet at 8 × 10 −17 erg s −1 cm −2 in 1000 s for galaxies at z = 1.4–1.6. We conclude with additional highlights from the on-sky validation and commissioning, key successes, and lessons learned.
Publisher: American Astronomical Society
Date: 2023
Abstract: The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect DESI spectra of approximately 2500 bright galaxies, 3500 luminous red galaxies (LRGs), and 10,000 emission-line galaxies (ELGs) to obtain robust redshift identifications. We then utilize the visually inspected redshift information to characterize the performance of the DESI operation. Based on the visual inspection (VI) catalogs, our results show that the final survey design yields s les of bright galaxies, LRGs, and ELGs with purity greater than 99%. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km s −1 for bright galaxies and ELGs and approximately 40 km s −1 for LRGs. The average redshift accuracy is within 10 km s −1 for the three types of galaxies. The VI process also helps improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show ex les of unexpected real astronomical objects, such as Ly α emitters and strong lensing candidates, identified by VI. These results demonstrate the importance and utility of visually inspecting data from incoming and upcoming surveys, especially during their early operation phases.
Publisher: Oxford University Press (OUP)
Date: 26-02-2019
DOI: 10.1093/MNRAS/STZ558
Location: United States of America
No related grants have been discovered for CHANGHOON HAHN.