The association of some short-duration gamma-ray bursts ( GRBs ) with elliptical galaxies established that their progenitors , unlike those of long GRBs , belong to an old stellar population .
However , the majority of short GRBs appear to occur in star forming galaxies , raising the possibility that some progenitors are related to recent star formation activity .
Here we present optical spectroscopy of these hosts and measure their luminosities , star formation rates , and metallicities .
We find luminosities of L _ { B } \approx 0.1 - 1.5 L _ { * } , star formation rates of { SFR } \approx 0.2 - 6 M _ { \odot } yr ^ { -1 } , and metallicities of 12 + { log ( O / H ) } \approx 8.5 - 8.9 ( Z \approx 0.6 - 1.6 Z _ { \odot } ) .
A detailed comparison to the hosts of long GRBs reveals systematically higher luminosities , lower specific star formation rates ( { SFR } / L _ { B } ) by about an order of magnitude , and higher metallicities by about 0.6 dex .
The K-S probability that the short and long GRB hosts are drawn from the same underlying galaxy distribution is only \sim 10 ^ { -3 } .
On the other hand , short GRB hosts exhibit excellent agreement with the specific star formation rates and the luminosity-metallicity relation of field galaxies at z \sim 0.1 - 1 .
We thus conclude that short GRB hosts are not dominated by young stellar populations like long GRBs hosts .
Instead , short GRB hosts appear to be drawn uniformly from the underlying galaxy distribution , indicating that the progenitors have a wide age distribution of several Gyr .