Other AGN

In general, I enjoy studying all types of AGN, over a variety of wavelengths. Below I highlight some of my other AGN projects.

Extended X-ray emission from the z=4.26 radio galaxy 4C 63.20

Most recently, BAYMAX was used in a study on 4C 63.20, which is a peculiar case of a high-redshift (z=4.261), radio-bright quasar. There is a mismatch between the number of observed, luminous, radio-loud quasars and the predicted radio-loud quasar density for high-redshift AGN, where are high redshift the observed number is ~3-10 times less than the prediction. This conundrum is often attributed to Cosmic Microwave Background (CMB) photons affecting the behavior of high-redshift jetted AGN. The two main effects of this are that (i) synchrotron emission is suppressed and (ii) high-energy electrons will cool effectively via inverse Compton scattering off CMB photons, enhancing X-ray emission and further suppressing the radio emission . The fact that 4C 63.20 has detected radio lobe emission, in spite of the strong assumed CMB energy density at the quasar's redshift, can be explained if the lobes are highly compact and/or magnetized. For such a system, CMB quenching models predict that the radio lobes should also be X-ray emitters and that the X-ray luminosity should be more luminous than for a comparably young and nearby radio galaxy. The stacked, 0.5-8 keV dataset was composed of less than 60 counts, making it difficult to measure the significance and location of any X-ray emission potentially coinciding with the radio lobes. Thus, we used BAYMAX to compare a single point source model (where X-ray emission is only consistent with the radio core) to a triple point source model (where the core and both radio lobes are emitting in X-rays). We found the Bayes factor strongly favored the triple point source model when using both non-informative and informative priors. Read more in Napier, Foord, Gallo et al. 2020.

VLA (5 Ghz; left), XMM-Newton (0.3-3 keV; center), and Chandra (0.5-8 keV; right) images of 4C 63.20. Given the resolution of XMM-Newton (6" FWHM at 1 keV), the X-ray image is consistent with a point source. Chandra observations show a spread of X-ray emission, consistent with position angle of the radio lobes. The system was analyzed with BAYMAX, where the triple point source model was strongly favored. Red circles, yellow open-faced triangles, and blue squared denote counts most likely associated with the core and two lobes (with red contours representing the error bars on their respective locations). Dashed boxes show the sky x, y, priors used for the location of each point source. Figures taken from Napier, Foord, Gallo et al. 2020.

SMBH Activity in Nucleated Galaxies

Motivated by theoretical expectations that nuclear star clusters (NSCs) in galactic centers provide a favorable environment for supermassive black holes to form and/or efficiently grow, I measured the fraction of nearby nucleated galaxies that also host an AGN. My nucleated galaxy sample consisted of both late-type and early-type galaxies. I found no statistically significant difference in the active fraction between the early- and late-type samples. Further, I found that the nucleated sample had an active fraction consistent with a parent sample of non-nucleated galaxies. My findings suggest that the presence of an NSC does not facilitate or enhance accretion-powered emission from a nuclear supermassive black hole. Read more in Foord et al. 2017a.

Five AGN that I discovered in the nucleated late-type sample, via analyzing their Chandra observations .