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

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

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

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 (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.

Original languageEnglish (US)
Article number58
JournalAstrophysical Journal
Volume905
Issue number1
DOIs
StatePublished - Dec 10 2020
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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