ORCID Profile
0000-0002-9808-3646
Current Organisation
E O Lawrence Berkeley National Laboratory
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Publisher: American Astronomical Society
Date: 07-12-2022
Abstract: A system of 5020 robotic fiber positioners was installed in 2019 on the Mayall Telescope, at Kitt Peak National Observatory. The robots automatically retarget their optical fibers every 10–20 minutes, each to a precision of several microns, with a reconfiguration time of fewer than 2 minutes. Over the next 5 yr, they will enable the newly constructed Dark Energy Spectroscopic Instrument (DESI) to measure the spectra of 35 million galaxies and quasars. DESI will produce the largest 3D map of the universe to date and measure the expansion history of the cosmos. In addition to the 5020 robotic positioners and optical fibers, DESI’s Focal Plane System includes six guide cameras, four wave front cameras, 123 fiducial point sources, and a metrology camera mounted at the primary mirror. The system also includes associated structural, thermal, and electrical systems. In all, it contains over 675,000 in idual parts. We discuss the design, construction, quality control, and integration of all these components. We include a summary of the key requirements, the review and acceptance process, on-sky validations of requirements, and lessons learned for future multiobject, fiber-fed spectrographs.
Publisher: American Astronomical Society
Date: 07-2022
Abstract: We analyze spatially resolved and co-added SDSS-IV MaNGA spectra with signal-to-noise ratio ∼100 from 2200 passive central galaxies ( z ∼ 0.05) to understand how central galaxy assembly depends on stellar mass ( M * ) and halo mass ( M h ). We control for systematic errors in M h by employing a new group catalog from Tinker and the widely used Yang et al. catalog. At fixed M * , the strengths of several stellar absorption features vary systematically with M h . Completely model-free, this is one of the first indications that the stellar populations of centrals with identical M * are affected by the properties of their host halos. To interpret these variations, we applied full spectral fitting with the code alf . At fixed M * , centrals in more massive halos are older, show lower [Fe/H], and have higher [Mg/Fe] with 3.5 σ confidence. We conclude that halos not only dictate how much M * galaxies assemble but also modulate their chemical enrichment histories. Turning to our analysis at fixed M h , high- M * centrals are older, show lower [Fe/H], and have higher [Mg/Fe] for M h 10 12 h −1 M ⊙ with confidence σ . While massive passive galaxies are thought to form early and rapidly, our results are among the first to distinguish these trends at fixed M h . They suggest that high- M * centrals experienced unique early formation histories, either through enhanced collapse and gas fueling or because their halos were early forming and highly concentrated, a possible signal of galaxy assembly bias.
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: American Astronomical Society
Date: 30-07-2020
Location: China
Location: United States of America
No related grants have been discovered for Kai Zhang.