(a) Mass-weighted merger rate of BBHs formed in dwarf galaxies. We depict the mass-weighted merger rate for dwarfs using the Panter et al. (2008) mean mass–metallicity relation, as well as the Andrews & Martini (2013) and the Lee et al. (2006) mass–metallicity relations. (b) For outer H I disks, we have shown the mass-weighted merger rate for the observed range of metallicities in outer H I disks.