Title: The Coevolution of Supermassive Black Holes and Galaxies since z~4


The discoveries of strong correlations between supermassive black hole and galaxy properties have greatly shaped our view that galaxy evolution and black hole activity are closely related. Using gravitational lenses and direct imaging methods, we are making important strides toward quantifying the black hole (MBH) vs. galaxy bulge mass (Mbulge) relation out to redshifts of ~4, and down to MBH~106 Msol in nearby galaxies. I will discuss our finding that the MBH-to-Mbulge ratio (at MBH > 108 Msol) increases at high redshifts. I will also discuss why selection biases do not weaken the conclusions. Another key evidence is that the sizes of the quasar host galaxies are highly compact compared to their mass -- a result which remarkably agrees with more recent studies of massive normal galaxies at the same epoch. Then, I will change gears to illustrate how galaxy merging can statistically produce salient features of the MBH vs. Mbulge relation virtually regardless of the initial conditions. An interesting prediction from models is that galaxies which have undergone more major mergers in the past preferentially lie on the tighter and more linear part of the MBH vs. Mtotal (total galaxy mass) relation. If, as widely believed, such merger histories tend to produce massive bulges, then statistics reveal that the more fundamental relation is actually that between the MBH and Mtotal, of which the tighter MBH-MBulge correlation is a special case. I compare predictions of statistical merging with measurements made through detailed analysis of nearby galaxies and AGNs. Taken together, these data indicate that the correlation between MBH vs. Mbulge deviates from linearity at low masses and that massive galaxies may have to grow by factors of 2-4 since redshift of 2-4.