The coevolution of supermassive black holes and galaxies at z ≥ 1: Galaxy morphology, gravitational lensing, and quasar hostgalaxies

Abstract

Supermassive black holes are ubiquitous in nearby galaxies. The strong correlations between black hole masses and their host galaxy bulges suggest they are intimately connected. To understand their coevolution we study quasars where both quantities can be probed out to high redshifts. To overcome the well known obstacles in studying quasar hosts at z > 1, we study 28 gravitationally lensed host galaxies, located at 1 ≤ zs ≤ 4.5, which are stretched out into arcs and Einstein rings. Applying two new algorithms, GALFIT and LENSFIT, to images obtained in the HST NICMOS F160W filter, we clearly resolve the host galaxies. Many have evidences of multiple components, interaction, offset galaxy components, or bulges and disks. The host galaxies at z > 1 are mostly brighter than L*V galaxies today, but would become fainter than L*V today after accounting for passive evolution. Furthermore, they have modest sizes (Re ≲ 6 kpc), and the profiles of the hosts are roughly equally split between bulge dominated and disk dominated. Due to these evidences, the quasar hosts may not be fully evolved early-type galaxies undergoing passive evolution if they evolve into L*V galaxies today. Moreover, comparing the hosts of radio-loud quasars and radio-quiet quasars, there is not a significant difference in their luminosities. Finally, we study the bulge luminosities (L(bulge)) and black hole masses (M(BH)) at z ≈ 1 and z ≈ 2, finding that the hosts at z > 2 already lie near the same L(bulge) vs. M(BH) relationship as for z = 0 normal galaxies . Accounting for an early-type galaxy evolution, they would fade below the relationship at present day. Therefore, the hosts at z ≈ 2 must undergo a stellar mass buildup by a factor of 3-5, if they evolve into early-type galaxies. This implies their M(BH)/M(bulge) ratio at z ≈ 2 is a factor of 3 higher than today. On the other hand, the L(bulge)-M(BH) relation for hosts at z ≈ 1 is consistent with early-type galaxies undergoing fading. Thus the parent population of the hosts at z = 2 may not be not the same as those at z = 1; the z = 2 hosts may either be progenitors of more typical late-type galaxies today, or must undergo significant stellar mass buildup.