Nicmos imaging of the host galaxies of z similar to 2-3 radio-quiet quasars

We have made a deep NICMOS imaging study of a sample of five z similar to 2 -3 radio-quiet quasars with low absolute nuclear luminosities, and we have detected apparent host galaxies in all of these. Most of the hosts have lum inosities approximately equal to present-day L-*, with a range from 0.2L(*) to about 4L(*). These host galaxies have magnitudes and sizes consistent w ith those of the Lyman break galaxies at similar redshifts and at similar r est wavelengths but are about 2 mag fainter than high-z powerful radio gala xies. The hosts of our high-z sample are comparable to or less luminous tha n the hosts of the low-z radio-quiet quasars with similar nuclear absolute magnitudes. However, the high-z galaxies are more compact than the hosts of the low-z quasars and probably have only 10%-20% of the stellar mass of th eir low-z counterparts. In one host, we find a residual component that is n ot centered on the quasar nucleus, and several hosts have apparent companio ns within a projected distance of similar to 10 kpc, indications that these systems are possibly in some phase of a merger process. Application of the M-bulge/M-BH relation found for present-day spheroids to the stellar masse s implied for the high-z host galaxies would indicate that they contain bla ck holes with masses around 10(8) M.. Comparison to their nuclear magnitude s implies accretion rates that are near or at the Eddington limit. Although these high-z hosts already contain supermassive black holes, the galaxies will need to grow significantly to evolve into present-day L-* galaxies. Th ese results are basically consistent with theoretical predictions for the h ierarchical buildup of the galaxy host and its relation to the central supe rmassive black hole.