Fundamental differences in the radio properties of red quasars (QSOs), as compared to blue QSOs, have been recently discovered, positioning them as a potential key population in the evolution of galaxies and black holes across cosmic time. To elucidate the nature of these objects, we exploited a rich compilation of broad-band photometry and spectroscopic data to model their spectral energy distributions (SEDs) from the ultraviolet to the far-infrared and characterise their emission-line properties. Following a systematic comparison approach, we characterise the properties of the QSO accretion, obscuration, and host galaxies in a sample of ∼1800 QSOs at 0.2 < z < 2.5, classified into red and control QSOs and matched in redshift and luminosity. We find no strong differences in the average multiwavelength SEDs of red and control QSOs, other than the reddening of the accretion disk expected by the colour selection. Additionally, no clear link can be recognised between the reddening of QSOs and the interstellar medium as well as star formation properties of their host galaxies. Our modelling of the infrared emission using dusty torus models suggests that the dust distributions and covering factors in red QSOs are strikingly similar to those of the control sample, inferring that the reddening is not related to the torus and orientation effects. Interestingly, we detect a significant excess of infrared emission at rest-frame 2−5 μm, which shows a direct correlation with optical reddening. To explain its origin, we investigated the presence of outflow signatures in the QSO spectra, discovering a higher incidence of broad [O III] wings and high C IV velocity shifts (> 1000 km s−1) in red QSOs as compared to the control sample. We find that red QSOs that exhibit evidence for high-velocity wind components present a stronger signature of the infrared excess, suggesting a causal connection between QSO reddening and the presence of hot dust distributions in QSO winds. We propose that dusty winds at nuclear scales are potentially the physical ingredient responsible for the optical colours in red QSOs, as well as a key parameter for the regulation of accretion material in the nucleus.

We examine possible environmental sources of the enhanced star formation and active galactic nucleus (AGN) activity in the z = 3.09 SSA22 protocluster using Hubble WFC3 F160W (∼1.6 μm) observations of the SSA22 field, including new observations centered on eight X-ray selected protocluster AGN. To investigate the role of mergers in the observed AGN and star formation enhancement, we apply both quantitative (Sérsic-fit and Gini-M 20 ) and visual morphological classifications to F160W images of protocluster Lyman-break galaxies (LBGs) in the fields of the X-ray AGN and z ∼ 3 field LBGs in SSA22 and GOODS-N. We find no statistically significant differences between the morphologies and merger fractions of protocluster and field LBGs, though we are limited by small number statistics in the protocluster. We also fit the UV-to-near-IR spectral energy distributions of F160W-detected protocluster and field LBGs to characterize their stellar masses and star formation histories. We find that the mean protocluster LBG is a factor of ∼2 times more massive and more attenuated than the mean z ∼ 3 field LBG. We take our results to suggest that ongoing mergers are not more common among protocluster LBGs than field LBGs, though protocluster LBGs appear to be more massive. We speculate that the larger mass of the protocluster LBGs contributes to the enhancement of SMBH mass and accretion rate in the protocluster, which in turn drives the observed protocluster AGN enhancement.Unified Astronomy Thesaurus concepts: High-redshift galaxy clusters (2007); High-redshift galaxies (734); Active galactic nuclei (16); X-ray active galactic nuclei (2035); Galaxy mergers (608)

Chris Harrison, James Trayford, Leigh Harrison and Nicolas Bonne have developed a sensory odyssey to demonstrate how the Universe can be made more accessible.

Abstract.We use the WISE all sky survey observations to look for counterparts of hard X-ray selected sources from the XMM-Newton-SDSS survey. We then measure the 12 μm luminosity of the AGN by decomposing their optical to infrared SEDs with a host and an AGN component and compare it to the X-ray luminosity and their expected intrinsic relation. This way we select 20 Xray under-luminous heavily obscured candidates and examine their X-ray and optical properties in more detail. We find evidence for a Compton-thick nucleus for six sources, a number lower than what expected from X-ray background synthesis models, which shows the limitations of our method. OverviewHeavily obscured and Compton-thick AGN are missing even in the deepest X-ray surveys, and indirect methods are required to detect them. Here we use a combination of the XMM-Newton serendipitous X-ray survey with the optical SDSS, and the WISE all-sky survey in order to check the efficiency of the low X-ray to infrared luminosity selection method in finding heavily obscured AGN. From the initial sample of 39830 X-ray sources on the footprint of the SDSS, we select the sources which are detected in the hard X-ray band (2-10 keV), and also have a redshift determination (photometric or spectroscopic) in the SDSS catalogue. We match this sample with the WISE catalogue, and fit the spectral energy distributions (SEDs) of the 2844 sources which have three, or more, photometric data-points in the infrared. We use the 2MASS and WISE photometry and perform a 2-component fit with a host and an AGN component to measure the midinfrared luminosity of the AGN. We then select the heavily obscured AGN candidates by comparing this to the observed 2-10 keV X-ray luminosity and the intrinsic relation between the X-ray and the mid-infrared luminosities. With this approach we find 20 candidate heavily obscured AGN and we then examine their SEDs in more detail using also the optical photometry and a stellar component, and also their X-ray and optical spectra. 8 out of the 12 candidates for which X-ray spectra can be fitted (67%) show signs of obscuration. Similarly 7 of the 9 sources for which we have [OIII] spectral information from the SDSS (78%) are classified as heavily obscured. Combining all three criteria, we determine the final number of heavily obscured AGN to be 15-20, and the number of Compton-thick AGN to be six. These numbers are smaller than what would be expected from X-ray background population synthesis models, which probably demonstrates how the optical-infrared selection limits the efficiency of selecting obscured AGN by their 245 available at https://www.cambridge.org/core/terms. https://doi

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