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Published September 20, 2010 | Published
Journal Article Open

Core-collapse Supernovae from the Palomar Transient Factory: Indications for a Different Population in Dwarf Galaxies


We use the first compilation of 72 core-collapse supernovae (SNe) from the Palomar Transient Factory (PTF) to study their observed subtype distribution in dwarf galaxies compared to giant galaxies. Our sample is the largest single-survey, untargeted, spectroscopically classified, homogeneous collection of core-collapse events ever assembled, spanning a wide host-galaxy luminosity range (down to M_r ≈ –14 mag) and including a substantial fraction (>20%) of dwarf (M_r ≥ –18 mag) hosts. We find more core-collapse SNe in dwarf galaxies than expected and several interesting trends emerge. We use detailed subclassifications of stripped-envelope core-collapse SNe and find that all Type I core-collapse events occurring in dwarf galaxies are either SNe Ib or broad-lined SNe Ic (SNe Ic-BL), while "normal" SNe Ic dominate in giant galaxies. We also see a significant excess of SNe IIb in dwarf hosts. We hypothesize that in lower metallicity hosts, metallicity-driven mass loss is reduced, allowing massive stars that would have appeared as "normal" SNe Ic in metal-rich galaxies to retain some He and H, exploding as Ib/IIb events. At the same time, another mechanism allows some stars to undergo extensive stripping and explode as SNe Ic-BL (and presumably also as long-duration gamma-ray bursts). Our results are still limited by small-number statistics, and our measurements of the observed N(Ib/c)/N(II) number ratio in dwarf and giant hosts (0.25^(+0.3)_(–0.15) and 0.23^(+0.11)_(–0.08), respectively; 1σ uncertainties) are consistent with previous studies and theoretical predictions. As additional PTF data accumulate, more robust statistical analyses will be possible, allowing the evolution of massive stars to be probed via the dwarf-galaxy SN population.

Additional Information

© 2010 The American Astronomical Society. Received 2010 April 16; accepted 2010 July 26; published 2010 September 1. The Weizmann Institute PTF partnership is supported by the Israeli Science Foundation via grants to A.G. Collaborative work between A.G. and S.R.K. is supported by the US–Israel Binational Science Foundation. A.G. further acknowledges support from the EU FP7 Marie Curie program via an IRG fellowship, the Benoziyo Center for Astrophysics, a Minerva grant, and the Peter and Patricia Gruber Awards. P.E.N. is supported by the US Department of Energy Scientific Discovery through Advanced Computing program under contract DEFG02- 06ER06-04. M.S. acknowledges support from the Royal Society; M.S. and A.G. are also grateful for a Weizmann-UK Making Connections grant. A.V.F. and S.B.C. acknowledge generous support from Gary and Cynthia Bengier, the Richard and Rhoda Goldman Fund, US National Science Foundation grant AST-0908886, and the TABASGO Foundation. J.S.B. was partially supported by a SciDAC grant from the US Department of Energy and a grant from the National Science Foundation (award 0941742). The National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under contract DE-AC02- 05CH11231, provided staff, computational resources, and data storage for this project. The WHT is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof´ısica de Canarias. 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. We are grateful to the staff of the Keck, Lick, Palomar, Roque de los Muchachos, VLT, and Gemini Observatories for their assistance.We thank Chris Lidman for processing theX-Shooter data used for the classification of PTF10bau.

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