Star formation inz> 1 3CR host galaxies as seen byHerschel

Abstract

We present Herschel (PACS and SPIRE) far-infrared (FIR) photometry of a complete sample of z > 1 3CR sources, from the Herschel guaranteed time project The Herschel Legacy of distant radio-loud AGN. 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, ULIRGstrength 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 orientationbased 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.

Observational evidence that positive and negative AGN feedback depends on galaxy mass and jet power

“…As we suggest in our model, at the highest radio powers negative feedback could lead to an overall suppression in SFR. In this case, Podigachoski et al (2015) results are in agreement with our model as both RGs and RLQs with similar radio luminosities share very similar SFRs, just like the RGs in this work. The fact that our RLQs could be characterized as moderate radio systems, at least compared to the RGs, can possible explain the reported SFRs differences.…”

“…2). Thus, our SFR estimations for the RG population are in perfect agreement (LFIR ∼ 10 11.7 L⊙) to the ones found by Podigachoski et al (2015), especially for their FIR-undetected sample if we consider that almost all of our RGs are FIR-undetected. In addition, our RG systems are also found to have SFRs that are quite similar to inactive galaxies selected from the deeper Herschel surveys (e.g.…”

“…In the same context, Drouart et al (2014) estimated SFRs of a few hundred to a few thousand solar masses per year for 1 < z < 5 radio galaxies. Recently, Podigachoski et al (2015), comparing the SFR of 3C radio-loud AGN and radio quasars at z > 1, found similar SFRs for the two classes and at the same levels with the previous works. The idea that the hosts of high-z radio-loud AGN can form stars at high rates is consistent with the jet-induced star formation model.…”

“…Seymour et al 2011;Dicken et al 2012;Magliocchetti et al 2014;Podigachoski et al 2015;Magliocchetti et al 2016). It also confirms and extends the high star-forming activity observed in the hosts of radio-active AGN selected by different methods (e.g.…”

“…Hatziminaoglou et al 2010;Santini et al 2012;Rosario et al 2013;Drouart et al 2014). For instance, Podigachoski et al (2015) use a sample of radio-loud objects that is similar in many ways to the dataset in this work, though they target more radio luminous systems. In term of source selection, both Podigachoski et al (2015) RGs and RLQs samples and our RGs are selected from bright radio surveys (e.g.…”