Searching for the Nearest Extragalactic Binary Black Hole: A Spectroscopic Study of NGC 4736
| dc.contributor.author | Gustafsson, Annika | |
| dc.date.accessioned | 2018-07-24T19:07:06Z | |
| dc.date.available | 2018-07-24T19:07:06Z | |
| dc.date.issued | 2015 | |
| dc.description | 24 pages | en_US |
| dc.description.abstract | Maoz et al. (1995,1996) concluded that the nearby galaxy NGC 4736 is in the late stages of a merger event. After further investigation, Maoz et al. (2005) observed variability in the nuclear region of NGC 4736, revealing a second unknown source of radiation in the nucleus. Since merging systems are an ideal location to search for binary black holes (BBH), we hypothesized that the second source could be a second black hole, making this a potential BBH system. Observational evidence for the existence of BBH remains sparse, even though BBH are predicted by many theories. 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-North telescope. We can classify the nature of the unknown source by looking at the optical line ratios following Ho et al. (1997). High signal-tonoise spectra of the unknown source displayed strong emission of [SII] and [NII], but extremely weak [OIII] emission. The unknown source has a calculated [NII]/[Hα] ratio of 1.37 and an upper limit of 0.6 for the [OIII]/[Hβ] ratio. Placing the unknown source on the BPT-NII diagram (Baldwin et al., 1981), we tentatively conclude that it is a second black hole potentially making NGC 4736 the nearest BBH system. The result will enable future observations of a low-luminosity system in extremely late stages of merging, which will be a significant step forward in validating models of galaxy mergers and AGN activity that further our understanding of galaxy formation and evolution. | en_US |
| dc.description.sponsorship | Oregon NASA Space Grant Consortium | en_US |
| dc.identifier.citation | Gustafsson, A. (2015). Searching for the Nearest Extragalactic Binary Black Hole: A Spectroscopic Study of NGC 4736. Oregon Undergraduate Research Journal, 9(1). doi:10.5399/uo/ourj.9.1.5 | en |
| dc.identifier.doi | 10.5399/uo/ourj.9.1.5 | en |
| dc.identifier.issn | 2160-617X | |
| dc.identifier.uri | https://hdl.handle.net/1794/23457 | |
| dc.language.iso | en | en_US |
| dc.publisher | University of Oregon | en_US |
| dc.rights | Creative Commons BY-NC-ND 4.0-US | en_US |
| dc.subject | Galaxy NGC 4736 | en_US |
| dc.subject | Black holes | en_US |
| dc.subject | Spectroscopy | en_US |
| dc.subject | Galaxy mergers | en_US |
| dc.title | Searching for the Nearest Extragalactic Binary Black Hole: A Spectroscopic Study of NGC 4736 | en_US |
| dc.type | Article | en_US |