Description
Supermassive black hole (SMBH) coalescence in galaxy mergers is believed to be one of the primary sources of very low frequency gravitational waves (GWs). Significant contribution of the GWs comes from mergers of massive galaxies with redshifts z<2. Very few previous studies gave the merger rate of massive galaxies. We selected a large sample (1209) of close pairs of galaxies with projected separations 7<r_p_<50kpc from 87889 luminous early-type galaxies (M_r_<-21.5) from the Sloan Digital Sky Survey Data Release 6. These pairs constitute a complete volume-limited sample in the local universe (z<0.12). Using our newly developed technique, 249 mergers have been identified by searching for interaction features. From them, we found that the merger fraction of luminous early-type galaxies is 0.8%, and the merger rate in the local universe is Rg~(1.0+/-0.4)x10^-5^Mpc^-3^/Gyr with an uncertainty mainly depending on the merging timescale.
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