Star formation in z>1 3CR host galaxies as seen by Herschel

TL;DR

This study uses Herschel and Spitzer data to analyze star formation in z>1 3CR radio-loud AGN host galaxies, revealing high star formation rates and similarities with non-AGN galaxies, challenging feedback quenching models.

Contribution

First infrared spectral analysis of z>1 3CR sources combining Herschel and Spitzer data, showing high star formation rates and similar properties to non-AGN galaxies at similar redshifts.

Findings

Approximately 40% of objects exhibit ULIRG-level star formation.

Quasar and radio galaxy hosts have similar FIR properties.

No strong evidence of star formation quenching in the sample.

Abstract

We present Herschel (PACS and SPIRE) far-infrared (FIR) photometry of a complete sample of z>1 3CR sources, from the Herschel GT project The Herschel Legacy of distant radio-loud AGN (PI: Barthel). Combining these with existing Spitzer photometric data, we perform an infrared (IR) spectral energy distribution (SED) analysis of these landmark objects in extragalactic research to study the star formation in the hosts of some of the brightest active galactic nuclei (AGN) known at any epoch. Accounting for the contribution from an AGN-powered warm dust component to the IR SED, about 40% of our objects undergo episodes of prodigious, ULIRG-strength star formation, with rates of hundreds of solar masses per year, coeval with the growth of the central supermassive black hole. Median SEDs imply that the quasar and radio galaxy hosts have similar FIR properties, in agreement with the orientation-based unification for radio-loud AGN. The star-forming properties of the AGN hosts are similar to those of the general population of equally massive non-AGN galaxies at comparable redshifts, thus there is no strong evidence of universal quenching of star formation (negative feedback) within this sample. Massive galaxies at high redshift may be forming stars prodigiously, regardless of whether their supermassive black holes are accreting or not.