Disentangling star formation and AGN activity in powerful infrared luminous radio galaxies at 1 <z< 4

Abstract

High-redshift radio galaxies present signs of both star formation and AGN activity, making them ideal candidates to investigate the connection and coevolution of AGN and star formation in the progenitors of present-day massive galaxies. We make use of a sample of 11 powerful radio galaxies spanning 1 < z < 4 which have complete coverage of their spectral energy distribution (SED) from UV to FIR wavelengths. Using Herschel data, we disentangle the relative contribution of the AGN and star formation by combining the galaxy evolution code PÉGASE.3 with an AGN torus model. We find that three components are necessary to reproduce the observed SEDs: an evolved and massive stellar component, a submm bright young starburst, and an AGN torus. We find that powerful radio galaxies form at very high-redshift, but experience episodic and important growth at 1 < z < 4 as the mass of the associated starburst varies from 5 to 50% of the total mass of the system. The properties of star formation differ from source to source, indicating no general trend of the star formation properties in the most infrared luminous high-redshift radio galaxies and no correlation with the AGN bolometric luminosity. Moreover, we find that AGN scattered light have a very limited impact on broad-band SED fitting on our sample. Finally, our analysis also suggests a wide range in origins for the observed star formation,which we partially constrain for some sources.

The mean star formation rates of unobscured QSOs: searching for evidence of suppressed or enhanced star formation

“…In agreement with previous results on radio selected AGN (e.g. Seymour et al 2011;Drouart et al 2014Drouart et al , 2016Kalfountzou et al 2014;Karouzos et al 2014;Magliocchetti et al 2014;Gürkan et al 2015;Podigachoski et al 2016), we find that the radio-luminous QSOs of our sample live in galaxies with significant on-going star formation. Even though we only have two luminosity bins in each redshift range, the L IR,SF values as a function of L 1.4 GHz are suggestive of a flat trend, further implying that the radio luminosity does not originate from the star formation in these systems and also indicating the lack of a direct relationship between the star formation emission of the galaxy and the radio emission of the QSOs.…”

“…FIR studies of radio AGN, with samples of HERG-type AGN, find that at z 0.2 their hosts have ongoing star formation, independent of selection methods (e.g. Seymour et al 2011;Drouart et al 2014Drouart et al , 2016Kalfountzou et al 2014;Karouzos et al 2014;Magliocchetti et al 2014;Gürkan et al 2015;Podigachoski et al 2016). Studies taking a luminosity cut where only the most luminous radio AGN are selected find evidence of intense FIR emission and star formation, at similar levels to the radio selected star-forming galaxies, at redshifts of z 1 (e.g.…”

Neutral versus ionized gas kinematics at z ≃ 2.6: the AGN-host starburst galaxy PKS 0529-549

“…Man et al 2018, in prep.). Drouart et al (2016) finds that 4C 41.17 is experiencing a recent starburst (∼30 Myr) which makes up ∼92% of the bolometric luminosity and forms ∼44% of the total stellar mass. Using this analogy and considering the large uncertainties, we adopt a conservative errorbar on the stellar mass of PKS 0529-549: M = (3.0 ± 2.0) × 10 11 M .…”

SHARP – VI. Evidence for CO (1–0) molecular gas extended on kpc-scales in AGN star-forming galaxies at high redshift

“…It is possible to study star-forming galaxies hosting an AGN through mapping their spectral energy distribution (SED), especially in the far-infrared (FIR) to near-infrared (NIR) wavelength range (1-1000 μm), where the AGN activity has several spectral features from the accretion disc, the hot torus, and the cold dust (e.g. Drouart et al 2016;Podigachoski et al 2016). Typically, the SED of a star-forming galaxy peaks at ∼100 μm, whereas when the dust is heated directly by the central AGN, the resulting peak in the thermal component dominates at shorter wavelengths, corresponding to a hotter effective dust temperature.…”