The Zwicky Transient Facility Bright Transient Survey I: Spectroscopic Classification and the Redshift Completeness of Local Galaxy Catalogs

Creators: Fremling, C.; Miller, A. A.; Sharma, Y.; Dugas, A.; Perley, D. A.; Taggart, K.; Sollerman, J.; Goobar, A.; Graham, M. L.; Neill, J. D.; Nordin, J.; Rigault, M.; Walters, R.; Andreoni, I.; Bagdasaryan, A.; Belicki, J.; Cannella, C.; Bellm, Eric C.; Cenko, S. B.; De, K.; Dekany, R.; Frederick, S.; Golkhou, V. Z.; Graham, M. J.; Helou, G.; Ho, A. Y. Q.; Kasliwal, M. M.; Kupfer, T.; Laher, R. R.; Mahabal, A.; Masci, F. J.; Riddle, R.; Rusholme, B.; Schulze, S.; Shupe, D. L.; Smith, R. M.; van Velzen, S.; Yan, Lin; Yao, Y.; Zhuang, Z.; Kulkarni, S. R.

Abstract

The Zwicky Transient Facility (ZTF) is performing a three-day cadence survey of the visible northern sky (~3π) with newly found transient candidates announced via public alerts. The ZTF Bright Transient Survey (BTS) is a large spectroscopic campaign to complement the photometric survey. BTS endeavors to spectroscopically classify all extragalactic transients with m_(peak) ≤ 18.5 mag in either the g_(ZTF) or r_(ZTF) filters, and publicly announce said classifications. BTS discoveries are predominantly supernovae (SNe), making this the largest flux-limited SN survey to date. Here we present a catalog of 761 SNe, classified during the first nine months of ZTF (2018 April 1–2018 December 31). We report BTS SN redshifts from SN template matching and spectroscopic host-galaxy redshifts when available. We analyze the redshift completeness of local galaxy catalogs, the redshift completeness fraction (RCF; the ratio of SN host galaxies with known spectroscopic redshift prior to SN discovery to the total number of SN hosts). Of the 512 host galaxies with SNe Ia, 227 had previously known spectroscopic redshifts, yielding an RCF estimate of 44% ± 4%. The RCF decreases with increasing distance and decreasing galaxy luminosity (for z < 0.05, or ~200 Mpc, RCF ≈ 0.6). Prospects for dramatically increasing the RCF are limited to new multifiber spectroscopic instruments or wide-field narrowband surveys. Existing galaxy redshift catalogs are only ~50% complete at r ≈ 16.9 mag. Pushing this limit several magnitudes deeper will pay huge dividends when searching for electromagnetic counterparts to gravitational wave events or sources of ultra-high-energy cosmic rays or neutrinos.

Additional Information

© 2020 The American Astronomical Society. Received 2019 October 28; revised 2020 March 16; accepted 2020 March 23; published 2020 May 21. We thank the anonymous referee for providing comments that improved this manuscript. Occasional observers on the UW APO ZTF follow-up team include Brigitta Sipocz, James Davenport, Daniela Huppenkothen, Dino Bektešević Gwendolyn Eadie, and Bryce T. Bolin. We thank students Shaney Sze and Ho Ko for assisting with candidate vetting during the summer of 2018. This work is based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. This work was supported by the GROWTH project funded by the National Science Foundation under PIRE grant No. 1545949. The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant #12540303 (PI: Graham). The Oskar Klein Centre is funded by the Swedish Research Council. C.F. gratefully acknowledges support of his research by the Heising-Simons Foundation (#2018-0907). A.A.M. is funded by the Large Synoptic Survey Telescope Corporation, the Brinson Foundation, and the Moore Foundation in support of the LSSTC Data Science Fellowship Program; he also receives support as a CIERA Fellow by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University). M.L.G. acknowledges support from the DiRAC Institute in the Department of Astronomy at the University of Washington. The DiRAC Institute is supported through generous gifts from the Charles and Lisa Simonyi Fund for Arts and Sciences, and the Washington Research Foundation. M.R. has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 759194—USNAC). S.V. is supported by the James Arthur Postdoctoral Fellowship. A.Y.Q.H. is supported by a National Science Foundation Graduate Research Fellowship under grant No. DGE1144469. A.G. and J.S. acknowledge support from the K&A Wallenberg foundation and the Swedish National Science foundation, VR. Partially based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. Some of the data presented here were obtained with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOTSA. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. This paper is partly based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Partially based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium. Partially based on observations from the LCOGT network. Partially based on public observations collected at the WHT, operated on the island of La Palma by the Isaac Newton Group. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. The SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. Software: SNID (Blondin & Tonry 2007), astropy (Astropy Collaboration et al. 2013), scipy (Virtanen et al. 2020), matplotlib (Hunter 2007), pandas (McKinney 2010), emcee (Foreman-Mackey et al. 2013), corner (Foreman-Mackey 2016), MultinomCI (Signorell et al. 2019), PYSEDM (Rigault et al. 2019), IRAF (Tody 1986), PyRAF (Science Software Branch at STScI 2012), pyraf-dbsp (Bellm & Sesar 2016), LPipe (Perley 2019), pyDIS (Davenport et al. 2016).

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