December 1, 2022 @ 14:00 – 15:00 Europe/Copenhagen Timezone

Why is colour special? Fundamental differences between red and blue quasars

An important fraction of quasars are red at optical wavelengths, indicating (in the vast majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In recent work by our group, we have shown fundamental differences in the radio properties of SDSS optically selected red quasars, which cannot be explained with a simple viewing angle hypothesis (Klindt et al. 2019, Fawcett et al. 2020, Rosario et al. 2020, Rosario et al. 2021, Fawcett et al. 2021). In our latest work, we use VLT/X-shooter spectroscopy of a sample of red and typical quasars to gain insight into these differences (Fawcett et al. 2022). We confirm that dust reddening is the main cause of the red colours and explore the emission line properties of our sample. We confront our spectra against accretion disc models and confirm that red quasars are powered by standard thin-disc accretion once corrected for dust extinction. These results suggest that dusty winds could be driving the fundamental differences in red quasars, and so they may represent an important phase in galaxy evolution. Using DESI spectra, we can now push to more extinguished, lower luminosity systems, which will test whether these results extend to more extreme reddened systems.