Search

We explore the distribution of R MS ≡ SFR/SFRMS (where SFRMS is the star formation rate of 'main-sequence' star-forming galaxies) for AGN hosts at |$z$|  = 1. We split our sample into two bins of X-ray luminosity divided at L X  = 2 × 1043 erg s−1 to investigate whether the R MS distribution changes as a function of AGN power. Our main results suggest that, when the R MS distribution of AGN hosts is modelled as a log-normal distribution (i.e. the same shape as that of MS galaxies), galaxies hosting more powerful X-ray AGNs (i.e. L X  > 2 × 1043 erg s−1) display a narrower R MS distribution that is shifted to higher values compared to their lower L X counterparts. In addition, we find that more powerful X-ray AGNs have SFRs that are more consistent with that of MS galaxies compared to lower L X AGNs. Despite this, the mean SFRs (as opposed to R MS) measured from these distributions are consistent with the previously observed flat relationship between SFR and L X . Our results suggest that the typical star-forming properties of AGN hosts change with L X , and that more powerful AGNs typically reside in more MS-like star-forming galaxies compared to lower L X AGNs. [ABSTRACT FROM AUTHOR]

In this study, we investigate the relationship between the star formation rate (SFR) and AGN luminosity (LAGN) for ~2000 X-ray detected AGN. The AGN span over three orders of magnitude in X-ray luminosity (1042 2-8 keV < 1045.5 erg s-1) and are in the redshift range z = 0.2-2.5. Using infrared (IR) photometry (8-500 µm), including deblended Spitzer and Herschel images and taking into account photometric upper limits, we decompose the IR spectral energy distributions into AGN and star formation components. Using the IR luminosities due to star formation, we investigate the average SFRs as a function of redshift and AGN luminosity. In agreement with previous studies, we find a strong evolution of the average SFR with redshift, tracking the observed evolution of the overall star-forming galaxy population. However, we find that the relationship between the average SFR and AGN luminosity is broadly flat at all redshifts and across all the AGN luminosities investigated; in comparison to previous studies, we find less scatter amongst the average SFRs across the wide range of AGN luminosities investigated. By comparing to empirical models, we argue that the observed flat relationship is due to short time-scale variations in AGN luminosity, driven by changes in the mass accretion rate, which wash out any underlying correlations between SFR and LAGN. Furthermore, we show that the exact form of the predicted relationship between SFR and AGN luminosity (and its normalization) is highly sensitive to the assumed intrinsic Eddington ratio distribution. [ABSTRACT FROM AUTHOR]

Dust-Obscured Galaxies (DOGs) are bright 24 μm-selected sources with extreme obscuration at optical wavelengths. They are typically characterized by a rising power-law continuum of hot dust (TD ∼ 200-1000 K) in the near-IR indicating that their mid-IR luminosity is dominated by an active galactic nucleus (AGN). DOGs with a fainter 24 μm flux display a stellar bump in the near-IR and their mid-IR luminosity appears to be mainly powered by dusty star formation. Alternatively, it may be that the mid-IR emission arising from AGN activity is dominant but the torus is sufficiently opaque to make the near-IR emission from the AGN negligible with respect to the emission from the host component. In an effort to characterize the astrophysical nature of the processes responsible for the IR emission in DOGs, this paper exploits Herschel data (PACS + SPIRE) on a sample of 95 DOGs within the COSMOS field. We derive a wealth of far-IR properties (e.g. total IR luminosities; mid-to-far-IR colours; dust temperatures and masses) based on spectral energy distribution fitting. Of particular interest are the 24 μm-bright DOGs (F24 μm > 1 mJy). They present bluer far-IR/mid-IR colours than the rest of the sample, unveiling the potential presence of an AGN. The AGN contribution to the total 8-1000 μm flux increases as a function of the rest-frame 8 μm-luminosity irrespective of the redshift. This confirms that faint DOGs (L8 μm < 1012 L⊙) are dominated by star formation while brighter DOGs show a larger contribution from an AGN. [ABSTRACT FROM AUTHOR]