A panchromatic view of infrared quasars: excess star formation and radio emission in the most heavily obscured systems. Issue 2 (3rd October 2022)

• Record Type: Journal Article
• Authors: Andonie, Carolina; Alexander, David M; Rosario, David; Laloux, Brivael; Georgakakis, Antonis; Morabito, Leah K; Villforth, Carolin; Avirett-Mackenzie, Mathilda; Rivera, Gabriela Calistro; Del Moro, Agnese; Fotopoulou, Sotiria; Harrison, Chris; Lapi, Andrea; Petley, James; Petter, Grayson; Shankar, Francesco
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 517:Issue 2(2022)
• Page Start: 2577
• Page End: 2598
• Publication Date: 2022-10-03
• Subjects: galaxies: active -- quasars: general -- infrared: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac2800
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: To understand the active galactic nuclei (AGNs) phenomenon and their impact on the evolution of galaxies, a complete AGN census is required; however, finding heavily obscured AGNs is observationally challenging. Here we use the deep and extensive multiwavelength data in the COSMOS field to select a complete sample of 578 infrared (IR) quasars ($L_{\rm AGN, IR}\gt 10^{45}\rm \: erg\: s^{-1}$ ) at z < 3, with minimal obscuration bias, using detailed UV-to-far-IR spectral energy distribution (SED) fitting. We complement our SED constraints with X-ray and radio observations to further investigate the properties of the sample. Overall, 322 of the IR quasars are detected by Chandra and have individual X-ray spectral constraints. From a combination of X-ray stacking and $L_{\rm 2-10\rm \, kev}$ – $L_{\rm 6\: \mu m}$ analyses, we show that the majority of the X-ray faint and undetected quasars are heavily obscured (many are likely Compton thick), highlighting the effectiveness of the mid-IR band to find obscured AGNs. We find that 355 (≈61 per cent) IR quasars are obscured ($N_{\rm H}\gt 10^{22}\rm \: cm^{-2}$ ) and identify differences in the average properties between the obscured and unobscured quasars: (1) obscured quasars have star formation rates ≈3 times higher than unobscured systems for no significant difference in stellar mass and (2) obscured quasars have stronger radio emission than unobscured systems, with a radio-loudness parameter $\approx 0.2 \rm \: dex$ higher. These results are inconsistent with a simple orientation model but in general agreement with either extreme host-galaxy obscuration towards the obscured quasars or a scenario where obscured quasars are an early phase in the evolution of quasars.