MEASURED METALLICITIES AT THE SITES OF NEARBY BROAD-LINED TYPE Ic SUPERNOVAE AND IMPLICATIONS FOR THE SUPERNOVAE GAMMA-RAY BURST CONNECTION

Abstract

We compare the chemical abundances at the sites of 12 nearby (z < 0.14) Type Ic supernovae (SN Ic) that showed broad lines, but had no observed gamma-ray burst (GRB), with the chemical abundances in five nearby (z < 0.25) galaxies at the sites of GRBs where broad-lined SN Ic were seen after the fireball had faded. It has previously been noted that GRB hosts are low in luminosity and low in their metal abundances. If low metallicity is sufficient to force the evolution of massive stars to end their lives as GRBs with an accompanying broad-lined SN Ic, then we would expect higher metal abundances for the broad-lined SN Ic that have no detected GRBs. This is what we observe, and this trend is independent of the choice of metallicity calibration we adopt and the mode of SN survey that found the broad-lined SN Ic. A unique feature of this analysis is that we present new spectra of the host galaxies and analyze all measurements of both samples in the same set of methods, using the galaxy emission-line measurements corrected for extinction and stellar absorption, via independent metallicity diagnostics of Kewley & Dopita, McGaugh, and Pettini & Pagel. In our small sample, the boundary between galaxies that have GRBs accompanying their broad-lined SN Ic and those that have broad-lined SN Ic without GRBs lies at an oxygen abundance of 12 + log(O/H) KD02 ∼ 8.5, which corresponds to 0.2-0.6 Z depending on the adopted metallicity scale and solar abundance value. Even when we limit the comparison to SN Ic that were found in untargeted supernova surveys, the environment of every broad-lined SN Ic that had no GRB is more metal rich than the site of any broad-lined SN Ic where a GRB was detected.

Stellar Forensics with the Supernova‐GRB Connection

“…The host environment of the most recent SN-GRB Starling et al 2011) is consistent with this trend. From Modjaz et al (2008a). 2010b) and one radio-relativistic SN, SN 2009bb (Soderberg et al 2010bLevesque et al 2010c) have been observed at high, super-solar, metallicity.…”

“…The next step was to compare the abundances of SNe Icbl with GRBs to SNe Ic-bl intrinsically without GRBs to test whether low metallicity is a necessary condition for GRB production. In 2007 and 2008 we embarked on directly measuring metallicities of a statistically significant sample of broad-lined SN Ic environments and deriving them in the same fashion, which we presented in our study of Modjaz et al (2008a), the first of its kind. There, we compared the chemical abundances at the sites of 5 nearby (z < 0.25) broad-lined SN Ic that accompany nearby GRBs with those of 12 nearby (z < 0.14) broad-lined SN Ic that have no observed GRBs.…”

“…Those prior metallicity studies do not directly probe the local environment of each SN (which can be different from the galaxy center due to metallicity gradients) nor do some differentiate between the different SN subtypes. In Modjaz et al (2011), we presented the largest existing set of host-galaxy spectra with H II region emission lines at the sites of 35 stripped-envelope core-collapse SNe and including those from the literature and from Modjaz et al (2008a), we analyzed the metallicity environments of a total of 47 stripped SNe. We derived local oxygen abundances in a robust manner in order to constrain the SN Ib/c progenitor population.…”

“…We derived local oxygen abundances in a robust manner in order to constrain the SN Ib/c progenitor population. We obtained spectra at the SN sites, included SNe from targeted and untargeted surveys, and performed the abundance determinations using the same three different oxygen-abundance calibrations as in Modjaz et al (2008a). We found that the sites of SNe Ic (the demise of the most heavily stripped stars having lost both H and He layers) are systematically more metal-rich than those of SNe Ib (arising from stars that retained their He layer) in all calibrations.…”

Probing the Interstellar Medium and Stellar Environments of Long-Duration GRBs

“…The GRB hosts also generally have sub-L * luminosities (Le Floc'h et al 2003;Fruchter et al 2006), consistent with low metallicities. Modjaz et al (2008) has, in addition, shown that GRBs occur in lower metallicity galaxies than the ones hosting a random sample of Type Ic SN. If this is confirmed, it would offer compelling evidence that metallicity plays a role in the GRB progenitors.…”