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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Del Moro, Agnese, Alexander, David M., Bauer, Franz E., Daddi, Emanuele, Kocevski, Dale D., Stanley, Flora & McIntosh, Daniel H. (2018). Luminous and Obscured Quasars and Their Host Galaxies. Frontiers in Astronomy and Space Sciences 4: 67.

Author(s) from Durham


The most heavily-obscured, luminous quasars might represent a specific phase of the evolution of the actively accreting supermassive black holes and their host galaxies, possibly related to mergers. We investigated a sample of the most luminous quasars at z ≈ 1 − 3 in the GOODS fields, selected in the mid-infrared band through detailed spectral energy distribution (SED) decomposition. The vast majority of these quasars (~80%) are obscured in the X-ray band and ~30% of them to such an extent, that they are undetected in some of the deepest (2 and 4 Ms) Chandra X-ray data. Although no clear relation is found between the star-formation rate of the host galaxies and the X-ray obscuration, we find a higher incidence of heavily-obscured quasars in disturbed/merging galaxies compared to the unobscured ones, thus possibly representing an earlier stage of evolution, after which the system is relaxing and becoming unobscured.