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The DESI Y1 RR Lyrae Catalog. I. Empirical Modeling of the Cyclic Variation of Spectroscopic Properties and a Chemodynamical Analysis of the Outer Halo
G. E. Medina (University of Toronto), Ting S. Li (University of Toronto), Sergey E. Koposov (University of Cambridge, University of Edinburgh), Alexander H. Riley (Durham University), Leandro José Beraldo e Silva (University of Arizona, University of Michigan), Monica Valluri (Hiroshima Shudo University, High Energy Accelerator Research Organization), Wenting Wang (Shanghai Jiao Tong University, Shanghai Key Laboratory for Particle Physics and Cosmology), Amanda Byström (University of Edinburgh), Oleg Y. Gnedin (Hiroshima Shudo University, High Energy Accelerator Research Organization), R. G. Carlberg (University of Toronto), Namitha Kizhuprakkat (National Tsing Hua University), B. A. Weaver (NSF NOIRLab), J. Aguilar (Lawrence Berkeley National Laboratory), Steven P. Ahlen (Boston University), Davide Bianchi (University of Milan, Brera Astronomical Observatory), D. Brooks (University College London), T. Claybaugh (Lawrence Berkeley National Laboratory), Andrew P. Cooper (National Tsing Hua University), Axel de la Macorra (Universidad Nacional Autónoma de México), Arjun T. Dey (NSF NOIRLab), P. Doel (University College London), Andreu Font-Ribera (Institute for High Energy Physics), J. E. Forero-Romero (Universidad de Los Andes), ENRIQUE GAZTAÑAGA (Institut d'Estudis Espacials de Catalunya, University of Portsmouth), Satya Gontcho A Gontcho (Lawrence Berkeley National Laboratory), G. Gutierrez (Fermi National Accelerator Laboratory), J. Guy (Lawrence Berkeley National Laboratory), K. Honscheid (University of Chicago, The Ohio State University), Mustapha Ishak (The University of Texas at Dallas), Theodore S. Kisner (Lawrence Berkeley National Laboratory), Martin Landriau (Lawrence Berkeley National Laboratory), Laurent Le Guillou (Sorbonne Université, Laboratoire de Physique Nucléaire et de Hautes Énergies), Aaron Meisner (NSF NOIRLab), R. Miquel (Institució Catalana de Recerca i Estudis Avançats, Institute for High Energy Physics), A. D. Myers (University of Wyoming), S. Nadathur (University of Portsmouth), Claire Poppett (Lawrence Berkeley National Laboratory, University of California System), Francisco Prada (Consejo Superior de Investigaciones Científicas, Universidad de Granada), Ignasi Pérez-Ràfols (Universitat Politècnica de Catalunya), G. Rossi (Sejong University), Eusebio Sanchez (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas), H. Seo (Ohio University), David Sprayberry (NSF NOIRLab), Gregory Tarlé (Hiroshima Shudo University, High Energy Accelerator Research Organization), Risa H. Wechsler (SLAC National Accelerator Laboratory, Kavli Institute for Particle Astrophysics and Cosmology), R. Zhou (Lawrence Berkeley National Laboratory), Hu Zou (Chinese Academy of Sciences)
Résumé : Abstract We present the catalog of RR Lyrae stars (RRLs) observed in the first year of operations of the Dark Energy Spectroscopic Instrument (DESI) survey. This catalog contains 6240 RRLs out to ∼120 kpc from the Galactic center and over 12,000 individual epochs with homogeneously derived stellar atmospheric parameters. We introduce a novel methodology to model the cyclical variation of the spectroscopic properties of RRLs from single-epoch measurements. We employ this method to infer the systemic velocities and mean temperatures of fundamental- and first-overtone-mode RRLs in our sample (without distinguishing between individual spectral lines). For fundamental-mode pulsators, we obtain radial velocity curves with amplitudes of ∼30–80 km s −1 and effective temperature curves with 300–1000 K variations, whereas for first-overtone pulsators these amplitudes are ∼20 km s −1 and ∼600 K, respectively. We use our sample to study the metallicity distribution of the halo and its dependence on Galactocentric distance ( R GC ). Using a radius-dependent mixture model, we split the data into chemodynamically distinct components and find that our inner halo sample ( R GC ≲ 50 kpc) is predominantly composed of stars with [Fe/H] ∼ −1.5 and largely radial orbits (with an anisotropy parameter β ∼ 0.94), which we associate with the Gaia–Sausage–Enceladus merger. Stars in the halo field exhibit a broader and more metal-poor [Fe/H] distribution with more circular orbits ( β ∼ 0.39). The metallicity gradient of the metal-rich and metal-poor components is found to be 0.005 and 0.010 dex kpc −1 , respectively. Our catalog highlights DESI’s tantalizing potential for studying the Milky Way and the pulsation properties of RRLs in the era of large spectroscopic surveys.