The DESI Y1 RR Lyrae Catalog. I. Empirical Modeling of the Cyclic Variation of Spectroscopic Properties and a Chemodynamical Analysis of the Outer Halo
Abstract
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.
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Authors: G. E. Medina, Ting S. Li, Sergey E. Koposov, Alexander H. Riley, Leandro José Beraldo e Silva, Monica Valluri, Wenting Wang, Amanda Byström, Oleg Y. Gnedin, R. G. Carlberg, Namitha Kizhuprakkat, B. A. Weaver, J. Aguilar, Steven P. Ahlen, Davide Bianchi, Donal Brooks, T. Claybaugh, Andrew P. Cooper, Axel de la Macorra, Arjun T. Dey, P. Doel, Andreu Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, Satya Gontcho A Gontcho, G. Gutierrez, J. Guy, K. Honscheid, Mustapha Ishak, Theodore S. Kisner, Martin Landriau, Laurent Le Guillou, Aaron Meisner, R. Miquel, A. D. Myers, S. Nadathur, Claire Poppett, F. Prada, Ignasi Pérez-Ràfols, Eusebio Sanchez, David Sprayberry, Gregory Tarlé, Risa H. Wechsler, Hu Zou
Institutions: Universidad Nacional Autónoma de México, University of Chicago, Shanghai Jiao Tong University, Chinese Academy of Sciences, The Ohio State University, University of Michigan, University of Toronto, Boston University, Consejo Superior de Investigaciones Científicas, University College London, University of Edinburgh, Ohio University, University of Arizona, Stanford University, Sorbonne Université, University of Cambridge, Institució Catalana de Recerca i Estudis Avançats, University of California, Berkeley, Universidad de Granada, Durham University, University of Wyoming, Universitat Politècnica de Catalunya, High Energy Accelerator Research Organization, University of Milan, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, National Tsing Hua University, University of Portsmouth, The University of Texas at Dallas, Sejong University, Lawrence Berkeley National Laboratory, Fermi National Accelerator Laboratory, Institut d'Estudis Espacials de Catalunya, NSF NOIRLab, SLAC National Accelerator Laboratory, Instituto de Astrofísica de Andalucía, National Institute for Astrophysics, Universidad de Los Andes, Kavli Institute for Particle Astrophysics and Cosmology, Brera Astronomical Observatory, Institute for High Energy Physics, National Observatory, Laboratoire de Physique Nucléaire et de Hautes Énergies, Hiroshima Shudo University, Shanghai Key Laboratory for Particle Physics and Cosmology