Presenter: Annika Gustafsson
Mentors: Scott Fisher and Elsa Johnson, Physics
Oral Presentation
Majors: Physics and Mathematics
Maoz et al. (1995, 1996) concluded that the nearby galaxy NGC 4736 is in the late stages of a merger event. After further investigation, in 2005, Maoz et al. observed ultraviolet variability in the nuclear region, implying the presence of a second unknown source. Since merging systems are an ideal location to search for binary black holes (BBHs), we hypothesize that the second unknown source here is a black hole, making this a BBH system. While the existence of BBHs are necessary for many theoretical predictions and play an important role in astrophysics, evidence for their existence remains sparse. To date, only NGC 6240 (Komossa et al., 2003) and Arp 299 (Ballo et al., 2004) have been discovered as merging galaxies with two active galactic nuclei (AGN). In 2008, NGC 4736 was observed with the Gemini Multi-Object Spectrograph on the Gemini North telescope. Optical spectra of the nuclear region were obtained with spatial resolution of 0.5’’. The two nuclear sources, at a projected separation of 2.5’’ are therefore spatially resolved (Maoz et al., 2005). As a result, we will attempt to classify the second source by analyzing optical line ratios following Ho et al., 1997. The line ratio value will allow us to definitely categorize the unknown source as a black hole if it falls correctly on the Baldwin, Phillips & Terlevich (BPT) diagram. At a distance of 4.9 Mpc, NGC 4736 would be the nearest BBH system, enabling high-spectral and spatial resolution observations. The distance and character of this possible BBH galaxy would be a significant step in allowing astrophysicists to validate models of galaxy mergers.