2020ApJ...892..153M

Unlike ordinary supernovae (SNe), some of which are hydrogen and helium deficient (called Type Ic SNe), broad-lined Type Ic SNe (SNe Ic-bl) are very energetic events, and only SNe Ic-bl are coincident with long-duration gamma-ray bursts (GRBs). Understanding the progenitors of SN Ic-bl explosions versus those of their SN Ic cousins is key to understanding the SN-GRB relationship and jet production in massive stars. Here we present the largest existing set of host galaxy spectra of 28 SNe Ic and 14 SNe Ic-bl, all discovered by the same galaxy-untargeted survey, namely, the Palomar Transient Factory (PTF). We carefully measure their gas-phase metallicities, stellar masses (M_*), and star formation rates (SFRs). We further reanalyze the hosts of 10 literature SN-GRBs using the same methods and compare them to our PTF SN hosts with the goal of constraining their progenitors from their local environments. We find that the metallicities, SFRs, and M_* values of our PTF SN Ic-bl hosts are statistically comparable to those of SN-GRBs but significantly lower than those of the PTF SNe Ic. The mass-metallicity relations as defined by the SNe Ic-bl and SN-GRBs are not significantly different from the same relations as defined by Sloan Digital Sky Survey galaxies, contradicting claims by earlier works. Our findings point toward low metallicity as a crucial ingredient for SN Ic-bl and SN-GRB production since we are able to break the degeneracy between high SFR and low metallicity. We suggest that the PTF SNe Ic-bl may have produced jets that were choked inside the star or were able to break out of the star as unseen low-luminosity or off-axis GRBs.