The Zwicky Transient Facility Census of the Local Universe. I. Systematic Search for Calcium-rich Gap Transients Reveals Three Related Spectroscopic Subclasses

Creators: De, Kishalay; Kasliwal, Mansi M.; Tzanidakis, Anastasios; Fremling, U. Christoffer; Adams, Scott; Aloisi, Robert; Andreoni, Igor; Bagdasaryan, Ashot; Bellm, Eric C.; Bildsten, Lars; Cannella, Christopher; Cook, David O.; Delacroix, Alexandre; Drake, Andrew; Duev, Dmitry; Dugas, Alison; Frederick, Sara; Gal-Yam, Avishay; Goldstein, Daniel; Golkhou, V. Zach; Graham, Matthew J.; Hale, David; Hankins, Matthew; Helou, George; Ho, Anna Y. Q.; Irani, Ido; Jencson, Jacob E.; Kaplan, David L.; Kaye, Stephen; Kulkarni, S. R.; Kupfer, Thomas; Laher, Russ R.; Leadbeater, Robin; Lunnan, Ragnhild; Masci, Frank J.; Miller, Adam A.; Neill, James D.; Ofek, Eran O.; Perley, Daniel A.; Polin, Abigail; Prince, Thomas A.; Quataert, Eliot; Reiley, Dan; Riddle, Reed L.; Rusholme, Ben; Sharma, Yashvi; Shupe, David L.; Sollerman, Jesper; Tartaglia, Leonardo; Walters, Richard; Yan, Lin; Yao, Yuhan

Abstract

Using the Zwicky Transient Facility alert stream, we are conducting a large spectroscopic campaign to construct a complete, volume-limited sample of transients brighter than 20 mag, and coincident within 100" of galaxies in the Census of the Local Universe catalog. We describe the experiment design and spectroscopic completeness from the first 16 months of operations, which have classified 754 supernovae. We present results from a systematic search for calcium-rich gap transients in the sample of 22 low-luminosity (peak absolute magnitude M > −17), hydrogen-poor events found in the experiment. We report the detection of eight new events, and constrain their volumetric rate to ≳ 15% ± 5% of the SN Ia rate. Combining this sample with 10 previously known events, we find a likely continuum of spectroscopic properties ranging from events with SN Ia–like features (Ca-Ia objects) to those with SN Ib/c–like features (Ca-Ib/c objects) at peak light. Within the Ca-Ib/c events, we find two populations distinguished by their red (g − r ≈ 1.5 mag) or green (g - r ≈ 0.5 mag) colors at the r-band peak, wherein redder events show strong line blanketing features and slower light curves (similar to Ca-Ia objects), weaker He lines, and lower [Ca ii]/[O i] in the nebular phase. We find that all together the spectroscopic continuum, volumetric rates, and striking old environments are consistent with the explosive burning of He shells on low-mass white dwarfs. We suggest that Ca-Ia and red Ca-Ib/c objects arise from the double detonation of He shells, while green Ca-Ib/c objects are consistent with low-efficiency burning scenarios like detonations in low-density shells or deflagrations.

Additional Information

© 2020. The American Astronomical Society. Received 2020 April 19; revised 2020 August 7; accepted 2020 August 25; published 2020 December 11. We thank the anonymous referee for a careful reading of the manuscript that helped significantly improve its content. We thank H. Perets, K. Shen, E.S. Phinney, J. Fuller, D. Kasen, B. Margalit, and S. Schulze for valuable discussions during this work. We thank M. Coughlin, S. Anand, A. Sagues Carracedo, L. Rauch, and U. Feindt for several discussions on the use of simsurvey. This work was supported by the GROWTH project funded by the National Science Foundation under Partnerships for International Research and Education (PIRE) grant no. 1545949. GROWTH is a collaborative project among Caltech (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK), and University of Sydney (Australia). This research benefited from interactions at several ZTF Theory Network meetings, funded by the Gordon and Betty Moore Foundation through grant GBMF5076. M.M.K. acknowledges generous support from the David and Lucille Packard Foundation. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the ZTF 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 Centre 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. SEDM is based upon work supported by the National Science Foundation under grant no. 1106171. The ZTF forced-photometry service was funded under Heising-Simons Foundation grant 12540303 (PI: Graham). Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among Caltech, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Based on observations made with NOT (operated by the Nordic Optical Telescope Scientific Association at Observatorio del Roque de los Muchachos, La Palma, Spain, of Instituto de Astrofisica de Canarias). A.G.Y.'s research is supported by the European Union via European Research Council grant no. 725161, the ISF GW Excellence Center, an IMOS space infrastructure grant, and BSF/Transformative and GIF grants, as well as The Benoziyo Endowment Fund for the Advancement of Science, the Deloro Institute for Advanced Research in Space and Optics, The Veronika A. Rabl Physics Discretionary Fund, Paul and Tina Gardner, Yeda-Sela, and the WIS–CIT joint research grant. A.G.Y. is a recipient of the Helen and Martin Kimmel Award for Innovative Investigation. A.Y.Q.H. is supported by a National Science Foundation Graduate Research Fellowship under grant no. DGE-1144469 and by the GROWTH project funded by the National Science Foundation under PIRE grant no. 1545949. R.L. is supported by a Marie Skłodowska-Curie Individual Fellowship within the Horizon 2020 EU Framework Programme for Research and Innovation (H2020-MSCA-IF-2017-794467). Foscgui is a graphic user interface aimed at extracting SN spectroscopy and photometry obtained with FOSC-like instruments. It was developed by E. Cappellaro. A package description can be found at http://sngroup.oapd.inaf.it/foscgui.html. Facilities: PO:1.2 m (ZTF) - , PO:1.5 m (SEDM) - , Hale (DBSP - , WaSP) - , NOT: ALFOSC - , THO: ALPY200 - , Keck:I (LRIS). - Software: astropy (Astropy Collaboration et al. 2013), matplotlib (Hunter 2007), scipy (Virtanen et al. 2020), pandas (McKinney 2010), SExtractor (Bertin & Arnouts 1996), scamp (Bertin 2006), SWarp (Bertin et al. 2002), PSFEx (Bertin 2011), pysedm (Rigault et al. 2019), pyraf-dbsp (Bellm & Sesar 2016), lpipe (Perley 2019), simsurvey (Feindt et al. 2019).

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