@article{0c5e289c7ddb4ab6ac72afdbbab7616b,
title = "High-quality Extragalactic Legacy-field Monitoring (HELM) with DECam: Project Overview and First Data Release",
abstract = "High-quality Extragalactic Legacy-field Monitoring (HELM) is a long-term observing program that photometrically monitors several well-studied extragalactic legacy fields with the Dark Energy Camera (DECam) imager on the CTIO 4 m Blanco telescope. Since 2019 February, HELM has been monitoring regions within COSMOS, XMM-LSS, CDF-S, S-CVZ, ELAIS-S1, and SDSS Stripe 82 with few-day cadences in the (u)gri(z) bands, over a collective sky area of ∼38 deg2. The main science goal of HELM is to provide high-quality optical light curves for a large sample of active galactic nuclei (AGNs), and to build decades-long time baselines when combining past and future optical light curves in these legacy fields. These optical images and light curves will facilitate the measurements of AGN reverberation mapping lags, as well as studies of AGN variability and its dependencies on accretion properties. In addition, the time-resolved and coadded DECam photometry will enable a broad range of science applications from galaxy evolution to time-domain science. We describe the design and implementation of the program and present the first data release that includes source catalogs and the first ∼3.5 yr of light curves during 2019A–2022A.",
author = "Zhuang, {Ming Yang} and Qian Yang and Yue Shen and Monika Adam{\'o}w and Friedel, {Douglas N.} and Gruendl, {R. A.} and Zachary Stone and Junyao Li and Xin Liu and Paul Martini and Abbott, {Timothy M.C.} and Anderson, {Scott F.} and Assef, {Roberto J.} and Bauer, {Franz E.} and Richard Bielby and Brandt, {W. N.} and Burke, {Colin J.} and Jorge Casares and Chen, {Yu Ching} and {De Rosa}, Gisella and Alex Drlica-Wagner and Tom Dwelly and Alice Eltvedt and Alvarez, {Gloria Fonseca} and Jianyang Fu and Cesar Fuentes and Graham, {Melissa L.} and Grier, {Catherine J.} and Nathan Golovich and Hall, {Patrick B.} and Patrick Hartigan and Keith Horne and Koekemoer, {Anton M.} and Mirko Krumpe and Li, {Jennifer I.} and Chris Lidman and Umang Malik and Amelia Mangian and Andrea Merloni and Claudio Ricci and Mara Salvato and Rob Sharp and Trilling, {David E.} and Tucker, {Brad E.} and Di Wen and Zachary Wideman and Yongquan Xue and Zhefu Yu and Catherine Zucker",
note = "This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Center for Cosmology and Astro-Particle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico and the Ministerio da Ciencia, Tecnologia e Inovacao, the Deutsche Forschungsgemeinschaft, and the Collaborating Institutions in the Dark Energy Survey. The collaborating institutions are Argonne National Laboratory, the University of California at Santa Cruz, the University of Cambridge, Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid, the University of Chicago, University College London, the DES-Brazil Consortium, the University of Edinburgh, the Eidgenossische Technische Hochschule (ETH) Zurich, Fermi National Accelerator Laboratory, the University of Illinois at Urbana-Champaign, the Institut de Ciencies de l\u2019Espai (IEEC/CSIC), the Institut de Fisica d\u2019Altes Energies, Lawrence Berkeley National Laboratory, the Ludwig Maximilians Universitat Munchen and the associated Excellence Cluster Universe, the University of Michigan, NSF\u2019s NOIRLab, the University of Nottingham, the Ohio State University, the University of Pennsylvania, the University of Portsmouth, SLAC National Accelerator Laboratory, Stanford University, the University of Sussex, and Texas A&M University. We thank Tamara M. Davis for initial discussions. This work is supported by NSF grants AST-2206499 and AST-2308077. R.J.A. was supported by FONDECYT grant No. 1231718 and by the ANID BASAL project FB210003. F.E.B. acknowledges support from ANID\u2014Millennium Science Initiative Program \u2014ICN12_009, CATA-BASAL\u2014FB210003, and FONDECYT Regular\u20141200495. Y.Q.X. acknowledges support from the National Key R&D Program of China (2023YFA1608100), NSFC grants (12025303, 12393814), and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB0550300).",
year = "2024",
month = oct,
day = "1",
doi = "10.3847/1538-4365/ad7d01",
language = "English (US)",
volume = "274",
journal = "Astrophysical Journal, Supplement Series",
issn = "0067-0049",
publisher = "American Astronomical Society",
number = "2",
}