Evidence for Early or Efficient Black-Hole Growth

Mass estimates, based on scaling relationships, are presented of central black holes in luminous quasars at a range of redshifts (z < 0.5, 1.2 ~< z ~< 6.3). The data show that very massive (about 10^9 solar masses or larger) black holes appear already at z ~ 6, indicating that they form very early or very fast.