Speaker: Victoria Fawcett
How are red and blue quasars different?
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). In our latest work, we use VLT/X-shooter spectroscopy of a sample of red and typical quasars to gain insight into these differences. 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 bedriving 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.
Speaker: Kathryn Neugent
Red Supergiant Binaries on the Path to Becoming Gravitational Wave Events
The detection of gravitational waves (GW) has ushered in a new era of astrophysics. While mergers of compact objects lead to these events, our understanding of the massive star progenitors is lacking. My PhD research focused on characterizing one subset of these progenitors: the evolved massive red supergiants (RSG) in binary systems. I'm now extending this research to explore both the direct GW progenitor systems of RSGs currently interacting with their companions (both stellar and compact objects), as well as the failed GW progenitor systems that end either in stellar mergers or RSGs with distant stellar companions. In this talk, I'll cover what we've learned so far about RSGs in binary systems and what the future holds in terms of identifying interacting systems and potential merger products. By comparing observations and population statistics of these various systems with predictions from current population synthesis models, soon we will know both how these GWs occur and how many we expect to detect in the future.