Extreme host galaxy growth in powerful early-epoch radio galaxies

TL;DR

This paper reports on Herschel Space Observatory observations revealing intense, obscured star-formation in the massive host galaxies of high-redshift radio-loud AGNs, suggesting rapid coeval galaxy and black hole growth in the early universe.

Contribution

It provides new observational evidence of vigorous star-formation in ultra-massive high-redshift radio galaxy hosts, highlighting a possible link between starburst activity and AGN evolution.

Findings

Star-formation rates of hundreds of solar masses per year in high-redshift radio galaxies.

Co-eval AGN and starburst activity indicating simultaneous galaxy and black hole growth.

Spectacular episodes of galaxy assembly during early cosmic epochs.

Abstract

During the first half of the universe's age, a heyday of star-formation must have occurred because many massive galaxies are in place after that epoch in cosmic history. Our observations with the revolutionary Herschel Space Observatory reveal vigorous optically obscured star-formation in the ultra-massive hosts of many powerful high-redshift 3C quasars and radio galaxies. This symbiotic occurrence of star-formation and black hole driven activity is in marked contrast to recent results dealing with Herschel observations of X-ray selected active galaxies. Three archetypal radio galaxies, at redshifts 1.132,1.575, and 2.474 are presented here, with inferred star-formation rates of hundreds of solar masses per year. A series of spectacular coeval AGN/starburst events may have formed these ultra-massive galaxies and their massive central black holes during their relatively short lifetimes.