2 research outputs found
The high-redshift clusters occupied by bent radio AGN (COBRA) survey
Galaxy clusters are the largest gravitationally-bound structures in the universe. Since clusters are comprised of hundreds of galaxies, hot X-ray emitting gas, and dark matter, they offer a unique laboratory in which to explore the evolution of large-scale structure and galaxies. To understand how massive, low-redshift galaxy clusters evolve to become what is observed in the modern universe, astronomers need to trace the evolution of progenitor clusters. Though there are thousands of well-studied low-redshift clusters, there are significantly fewer spectroscopically confirmed high-redshift clusters.
Because most massive galaxies host supermassive black holes, one cluster tracer at both low and high redshift are active galactic nuclei (AGNs). Specifically, bent, double-lobed radio sources are commonly found in clusters. I find high-redshift clusters hosting bent AGNs and explore their evolution and red sequence galaxies over cosmic time. To characterize cluster evolution, I examine the galaxy populations surrounding each AGN to determine if bent AGNs are commonly found within clusters with evolved red sequence populations. I then identify evolution among the member galaxies in the clusters, I estimate cluster morphology, and I explore the relationship between bent radio source morphology and the surrounding cluster.
By measuring the color of each galaxy and the overdensity of galaxies surrounding each AGN, I identify 39 red sequence cluster candidates, 17 of which are at redshifts of z > 1.0. Using my red sequence surface density measurement, I show that each bent AGN is not necessarily centrally located, but is generally within ~ 400 kpc of the cluster center. With this sample, I probe the dynamics of the host galaxies using the radio source morphology and find that most of the radio sources do not follow radial paths relative to the cluster center. By analyzing the morphology of the radio sources in my sample, I find that richer clusters host narrower bent sources. I also see a range of red sequence populations in the clusters, with variations, in particular, among the populations of faint red sequence galaxies. With my surface density measurements, I place preliminary constraints on cluster morphology, finding both relaxed and merging systems
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Inspiraling streams of enriched gas observed around a massive galaxy 11 billion years ago
A tidal disruption event (TDE) occurs when a supermassive black hole rips apart a passing star. Part of the stellar material falls toward the black hole, forming an accretion disk that in some cases launches a relativistic jet. We performed optical polarimetry observations of a TDE, AT 2020mot. We find a peak linear polarization degree of 25 ± 4%, consistent with highly polarized synchrotron radiation, as is typically observed from relativistic jets. However, our radio observations, taken up to 8 months after the optical peak, do not detect the corresponding radio emission expected from a relativistic jet. We suggest that the linearly polarized optical emission instead arises from shocks that occur during accretion disk formation, as the stream of stellar material collides with itself.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]