Role of active galactic nuclei in the luminous infrared galaxy phase at z ≤ 3. Issue 3 (31st December 2015)

• Record Type: Journal Article
• Authors: Lin, Ming-Yi; Hashimoto, Yasuhiro; Foucaud, Sébastien
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 456:Issue 3(2016)
• Page Start: 2735
• Page End: 2748
• Publication Date: 2015-12-31
• Subjects: galaxies: active -- galaxies: high-redshift -- infrared: galaxies -- X-rays: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stv2766
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract : To understand the interactions between active galactic nuclei (AGNs) and star formation during the evolution of galaxies, we investigate 142 galaxies detected in both X-ray and 70 μm observations in the COSMOS (Cosmic Evolution Survey) field. All of our data are obtained from the archive X-ray point-source catalogues from Chandra and XMM–Newton observations, and the far-infrared 70 μm point-source catalogue from Spitzer-MIPS observations. Although the IRAC [3.6 μm]–[4.5 μm] versus [5.8 μm]–[8.0 μm] colours of our sample indicate that only ∼63 per cent of our sources would be classified as AGNs, the ratio of the rest-frame 2–10 keV luminosity to the total infrared luminosity (8–1000 μm) shows that the entire sample has comparatively higher X-ray luminosity than that expected from pure star-forming galaxies, suggesting the presence of an AGN in all of our sources. From an analysis of the X-ray hardness ratio, we find that sources with both 70 μm and X-ray detection tend to have a higher hardness ratio relative to the whole X-ray-selected source population, suggesting the presence of more X-ray absorption in the 70 μm detected sources. In addition, we find that the observed far-infrared colours of 70 μm detected sources with and without X-ray emission are similar, suggesting the far-infrared emission could be mainly powered by star formation.