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Full list of authors: Lan, Ting-Wen; Tojeiro, R.; Armengaud, E.; Prochaska, J. Xavier; Davis, T. M.; Alexander, David M.; Raichoor, A.; Zhou, Rongpu; Yeche, Christophe; Balland, C.; BenZvi, S.; Berti, A.; Canning, R.; Carr, A.; Chittenden, H.; Cole, S.; Cousinou, M. -c.; Dawson, K.; Dey, Biprateep; Douglass, K.; Edge, A.; Escoffier, S.; Glanville, A.; Gontcho, S. Gontcho; Guy, J.; Hahn, C.; Howlett, C.; Hwang, Ho Seong; Jiang, L.; Kovacs, A.; Mezcua, M.; Moore, S.; Nadathur, S.; Oh, M.; Parkinson, D.; Rocher, A.; Ross, A. J.; Ruhlmann-Kleider, V.; Sabiu, C. G.; Said, K.; Saulder, C.; Sierra-Porta, D.; Weiner, B.; Yu, J.; Zarrouk, P.; Zhang, Y.; Zou, H.; Ahlen, S.; Bailey, S.; Brooks, D.; Cooper, A. P.; de la Macorra, A.; Dey, A.; Dhungana, G.; Doel, P.; Eftekharzadeh, S.; Fanning, K.; Font-Ribera, A.; Garrison, L.; Gaztanaga, E.; Kehoe, R.; Kisner, T.; Kremin, A.; Landriau, M.; Le Guillou, L.; Levi, Michael E.; Magneville, C.; Meisner, Aaron M.; Miquel, R.; Moustakas, J.; Myers, Adam D.; Newman, Jeffrey A.; Nie, J. D.; Palanque-Delabrouille, N.; Percival, W. J.; Poppett, C.; Prada, F.; Schubnell, M.; Tarle, Gregory; Weaver, B. A.; Zhang, K.; Zhou, Zhimin.--This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., 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 samples 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 examples of unexpected real astronomical objects, such as Lyα 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. © 2023. The Author(s). Published by the American Astronomical Society., W.L. is supported by the Ministry of Science and Technology (MOST 111-2112-M-002-015-MY3), the Ministry of Education, Taiwan (MOE Yushan Young Scholar grant Nos. NTU-110VV007 and NTU-110VV007-2), National Taiwan University research grant Nos. NTU-CC-111L894806, NTU-111L7318, and NTU-112L7302 and NSF grant No. AST-1911140. D.M.A. acknowledges the Science Technology and Facilities Council (STFC) for support through grant No. ST/T000244/1. This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under contract No. DE-AC02-05CH11231, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under contract No. AST-0950945 to the NSF's National Optical-Infrared Astronomy Research Laboratory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico (CONACYT); the Ministry of Science and Innovation of Spain (MICINN), and by the DESI Member Institutions: https://www.desi.lbl.gov/collaborating-institutions., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).

First draft; To be submitted to ApJ Preprint typeset using L A TEX style emulateapj v. 5/2/11 SHADOW OF A COLOSSUS: A z = 2.45 GALAXY PROTOCLUSTER DETECTED IN 3D Lyα FOREST TOMOGRAPHIC MAPPING OF THE COSMOS FIELD Khee-Gan Lee 1 , Joseph F. Hennawi 1 , Martin White 2,3 , J. Xavier Prochaska 4,5 , Andreu Font-Ribera 3 , ` vre 8 , David J. Schlegel 3 , R. Michael Rich 6 , Nao Suzuki 7 , Casey W. Stark 2,3 , Olivier Le F e Peter E. Nugent , Mara Salvato Gianni Zamorani , arXiv:1509.02833v1 [astro-ph.CO] 9 Sep 2015 First draft; To be submitted to ApJ ABSTRACT Using moderate-resolution optical spectra from 58 background Lyman-break galaxies and quasars at z ∼ 2.3 − 3 within a 11.5 0 × 13.5 0 area of the COSMOS field (∼ 1200 deg −2 projected area density or ∼ 2.4 h −1 Mpc mean transverse separation), we reconstruct a 3D tomographic map of the foreground Lyα forest absorption at 2.2 2) galaxy protoclus- ters is a topic of increasing interest, providing a route to studying galaxy evolution, AGN, plasma physics, and our models of gravity. They are also critical laboratories for understanding the growth of massive galaxy clusters at z ∼ 0. While many studies have successfully found pro- toclusters around active supermassive black holes such as radio galaxies or luminous quasars (see Hennawi et al. lee@mpia.de 1 Max Planck Institute for Astronomy, K¨ onigstuhl 17, D-69117 Heidelberg, West Germany 2 Department of Astronomy, University of California at Berke- ley, B-20 Hearst Field Annex # 3411, Berkeley, CA 94720, USA 3 Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, USA 4 Department of Astronomy and Astrophysics, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA 5 University of California Observatories, Lick Observatory, 1156 High Street, Santa Cruz, CA 95064, USA 6 Department of Physics and Astronomy, University of Cali- fornia at Los Angeles, Los Angeles, CA 90095-1562, USA 7 Kavli Institute for the Physics and Mathematics of the Uni- verse (IPMU), The University of Tokyo, Kashiwano-ha 5-1-5, Kashiwa-shi, Chiba, Japan 8 Aix Marseille Universit´ e, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388, Marseille, France 9 Max Planck Institute for Extraterrestrial Physics, Giesen- bachstrae 1, 85741 Garching bei M¨ unchen, Germany 10 INAF–Osservatorio Astronomico di Bologna, via Ranzani,1, I-40127, Bologna, Italy 2015 and Cooke et al. 2014 for recent examples, or Chi- ang et al. 2013 for a compilation), it is difficult to tell whether these ‘signpost’ protoclusters are representative of the overall population – which, at least in simulations, shows a wide range of properties. More uniform, ‘blind’, search techniques are therefore required for unbiased samples of protoclusters. Several such objects have been found serendipitously in pho- tometric or galaxy redshift surveys (e.g., Steidel et al. 2005; Gobat et al. 2011; Cucciati et al. 2014; Yuan et al. 2014; Casey et al. 2015). Searching photometric redshift catalogs (Chiang et al. 2014) is another promising new technique, but is limited to fields with extensive multi- wavelength photometry that enable accurate photomet- ric redshfits. Unfortunately we expect protoclusters to be rare, and surveying large volumes of space with these techniques is expensive. Recently, Stark et al. (2015b) (hereafter S15) argued that 3D tomographic reconstructions of the intergalactic medium (IGM) Lyman-α (Lyα) forest absorption (Pi- chon et al. 2001; Caucci et al. 2008; Lee et al. 2014a) can be used to efficiently search for protoclusters. A protocluster’s Lyα absorption signature extends over a large region (r & 5 h −1 Mpc) allowing it to be mapped by background galaxies separated by several transverse Mpc, corresponding to relatively bright limiting magni- tudes (. 24.5 mag) and therefore accessible to existing 8-10m class telescopes. In fact several studies have al- ready found Lyα absorption associated with protoclus

We report the detection of a strong Milky Way-type 2175 \AA$ $ extinction bump at $z$ = 2.1166 in the quasar spectrum towards SDSS J121143.42+083349.7 from the Sloan Digital Sky Survey (SDSS) Data Release 10. We conduct follow up observations with the Echelle Spectrograph and Imager (ESI) onboard the Keck-II telescope and the Ultraviolet and Visual Echelle Spectrograph (UVES) on the VLT. This 2175 \AA$ $ absorber is remarkable in that we simultaneously detect neutral carbon (C I), neutral chlorine (Cl I), and carbon monoxide (CO). It also qualifies as a damped Lyman alpha system. The J1211+0833 absorber is found to be metal-rich and has a dust depletion pattern resembling that of the Milky Way disk clouds. We use the column densities of the C I fine structure states and the C II/C I ratio (under the assumption of ionization equilibrium) to derive the temperature and volume density in the absorbing gas. A Cloudy photoionization model is constructed, which utilizes additional atoms/ions to constrain the physical conditions. The inferred physical conditions are consistent with a canonical cold (T $\sim$ 100 K) neutral medium with a high density ($n$(H I) $\sim$ 100 cm$^{-3}$) and a slightly higher pressure than the local interstellar medium. Given the simultaneous presence of C I, CO, and the 2175 \AA$ $ bump, combined with the high metallicity, high dust depletion level and overall low ionization state of the gas, the absorber towards J1211+0833 supports the scenario that the presence of the bump requires an evolved stellar population., Comment: 18 pages, 17 figures, to be published in MNRAS