The VLA-COSMOS 3 GHz Large Project: AGN and host-galaxy properties out toz ≲ 6

Abstract

We explore the multiwavelength properties of AGN host galaxies for different classes of radio-selected AGN out to z 6 via a multiwavelength analysis of about 7 700 radio sources in the COSMOS field. The sources were selected with the Very Large Array (VLA) at 3 GHz (10 cm) within the VLA-COSMOS 3 GHz Large Project, and cross-matched with multiwavelength ancillary data. This is the largest sample of highredshift (z 6) radio sources with exquisite photometric coverage and redshift measurements available. We constructed a sample of moderate-tohigh radiative luminosity AGN (HLAGN) via spectral energy distribution (SED) decomposition combined with standard X-ray and mid-infrared diagnostics. Within the remainder of the sample we further identified low-to-moderate radiative luminosity AGN (MLAGN) via excess in radio emission relative to the star formation rates in their host galaxies. We show that at each redshift our HLAGN have systematically higher radiative luminosities than MLAGN and that their AGN power occurs predominantly in radiative form, while MLAGN display a substantial mechanical AGN luminosity component. We found significant differences in the host properties of the two AGN classes, as a function of redshift. At z<1.5, MLAGN appear to reside in significantly more massive and less star-forming galaxies compared to HLAGN. At z>1.5, we observed a reversal in the behaviour of the stellar mass distributions with the HLAGN populating the higher stellar mass tail. We interpret this finding as a possible hint of the downsizing of galaxies hosting HLAGN, with the most massive galaxies triggering AGN activity earlier than less massive galaxies, and then fading to MLAGN at lower redshifts. Our conclusion is that HLAGN and MLAGN samples trace two distinct galaxy and AGN populations in a wide range of redshifts, possibly resembling the radio AGN types often referred to as radiative-and jet-mode (or high-and low-excitation), respectively, whose properties might depend on the different availability of cold gas supplies.

The role of galaxy mass on AGN emission: a view from the VANDELS survey

“…Indeed, for radio-emitting sources our data mirrors the wellknown result for radio-active AGN to preferentially reside in galaxies of large, M * ∼ > 10 10 M , stellar content (e.g. Best et al 2005;Smolcic et al 2009;Magliocchetti et al 2014;Smolcic et al 2017;Delvecchio et al 2017;Sabater et al 2019). A similar trend (even though with a much wider mass distribution -cfr Figure 9) is also present in the behavior of X-ray-selected sources and is due to the combination of observational bias effects with the fact that AGN are 2 Note that the masses computed in VANDELS do not include an AGN component in the SED-fitting procedure.…”

SCUBA-2 Ultra Deep Imaging EAO Survey (Studies). III. Multiwavelength Properties, Luminosity Functions, and Preliminary Source Catalog of 450 μm Selected Galaxies

“…To determine AGN contamination at radio wavelength, we follow Equation 1 in Delvecchio et al (2017), which describes a redshift dependent threshold in radioexcess. In brief, they first excluded the luminous AGN populations according to X-ray, mid-infrared, or opticalto-FIR SED decomposition from the VLA 3 GHz catalog.…”

Automated Mining of the ALMA Archive in the COSMOS Field (A3COSMOS). I. Robust ALMA Continuum Photometry Catalogs and Stellar Mass and Star Formation Properties for ∼700 Galaxies at z = 0.5–6

“…We show the comparison of these redshifts (hereafter prior redshift, or "prior-z") in Fig. 21, where Davidzon et al (2017) photometric catalog for the same UltraVISTA galaxies as Laigle et al (2016) but with optimized SED fitting for z > 2.5 sources; the Delvecchio et al (2017) photometric catalog for radio-detected galaxies; and the Salvato et al (2011) photometric catalog for X-ray-detected active galactic nuclei (AGNs).…”

“…We use MAGPHYS (da Cunha et al 2008 22 for the SED fitting, as it has rich stellar SED libraries and has been widely tested on local and high-redshift galaxies (e.g., Smith et al 2012;Berta et al 2013;Rowlands et al 2014b,a;Smolčić et al 2015;Miettinen et al 2017a,b;Delvecchio et al 2017;Hunt et al 2019). It assumes an energy balance between the energy attenuated by dust in the UV/optical and that radiated by dust at IR/mm wavelengths.…”