Formation Redshift of the Massive Black Holes Detected by LIGO

Abstract

We compare the event rate density detected by LIGO to the comoving number density of isolated stellar progenitors and find a range for their formation redshift. Our limit depends on the threshold mass for making the black holes (BHs) but only weakly on the metallicity of their progenitor. If $10\%$ of all BHs are in coalescing binaries, then enough progenitors have formed by $2<z_f<9$.

Comments: 4 pages, 2 figures