The host galaxies of the five local , z \leq 0.25 , long-duration gamma-ray bursts ( GRBs 980425 , 020903 , 030329 , 031203 and 060218 ) , each of which had a well-documented associated supernova , are all faint and metal-poor compared to the population of local star-forming galaxies .
We quantify this statement by using a previous analysis of star-forming galaxies ( 0.005 < z < 0.2 ) from the Sloan Digital Sky Survey to estimate the fraction of local star formation as a function of host galaxy oxygen abundance .
We find that only a small fraction ( < 25 % ) of current star formation occurs in galaxies with oxygen abundance 12 + \log { ( O / H ) } < 8.6 , i.e. , about half that of the Milky Way .
However , all five low- z GRB hosts have oxygen abundance below this limit , in three cases very significantly so .
If GRBs traced local star formation independent of metallicity , the probability of obtaining such low abundances for all five hosts would be p \approx 0.1 % .
We conclude that GRBs trace only low-metallicity star formation , and that the Milky Way has been too metal rich to host long GRBs for at least the last several billion years .
This result has implications for the potential role of GRBs in mass extinctions , for searches for recent burst remnants in the Milky Way and other large galaxies , for non-detections of late radio emission from local core-collapse supernovae , and for the production of cosmic rays in the local Universe .
Our results agree with theoretical models that tie GRBs to rapidly spinning progenitors , which require minimal angular momentum loss in stellar winds .
We also find that the isotropic energy release of these five GRBs , E _ { iso } , steeply decreases with increasing host oxygen abundance .
This might further indicate that ( low ) metallicity plays a fundamental physical role in the GRB phenomenon , and suggesting an upper metallicity limit for “ cosmological ” GRBs at \sim 0.15 { Z _ { \odot } } .