Subcategory: Astronomy and Astrophysics
Kaitlynn Lilly - University of Maryland, Baltimore County
Co-Author(s): David Sanders, Connor Auge, Institute for Astronomy, University of Hawaii at Manoa
At the center of nearly every galaxy lies a supermassive black hole (SMBH). The histories of these SMBHs represent a critical aspect of galaxy evolution across cosmic time. The growth of SMBHs takes place in active galactic nuclei (AGN), which can be identified by their luminous X-ray emission (LX > 1043 ergs/s). Luminous AGN appear to be connected to violent events, in particular to strong interactions and mergers of gas-rich galaxies. In order to determine the relationship that SMBHs have to their host galaxy morphology and discover how the SMBHs grow and evolve, we first visually classified the strength of different morphological features (point-nucleus, spheroid, merger/irregular) of a large unbiased sample of 1075 galaxies from the Cosmic Evolution Survey (COSMOS). Our results are that mergers and irregulars make up 28% of the total sample of AGN, while prominent spheroid sources (of which ¾ had a strong nuclear point source) comprise 71% of the sample. Spectral energy distributions (SEDs) were constructed for each source using the extensive photometric coverage provided by the COSMOS survey (typically 30 continuum data points per source from X-ray to radio wavelengths), and the strengths of traditional optically-selected AGN features, e.g. excess UV emission from the accretion disk and excess NIR emission from a dusty torus, were measured. We find that ALL merger/irregular sources show NO excess UV emission, and only a modest NIR excess. In contrast, the majority of sources with strong point nuclei and prominent spheroids have enhanced UV and NIR features. In addition, we find that the strength of the AGN features increases with X-ray luminosity. Our results are consistent with the hypothesis that the UV and NIR signatures are obscured during early merger stages and increase in strength during later stages when the spheroid and nuclear point-source become increasingly visible as the SMBH continues to increase in mass. In the future, we hope to expand our analysis to a much larger sample of X-ray luminous sources, including both lower and higher X-ray luminosities, in order to better understand the complete growth histories of SMBHs as well as the possible relationship of X-ray selected AGN to other classes of extragalactic objects. References: Hickox, R. C., & Alexander, D. M. 2018. Obscured Active Galactic Nuclei ARA&A, 56, 625 Hung, C.-L., Sanders, D. B., Casey, C. M., et al. 2013. The Role of Galaxy Interaction in the SFR-M Relation. ApJ, 778, 129 Laigle, C., McCracken, H. J., Ilbert, O., et al. 2016. The COSMOS2015 Catalog: Exploring the 1< z <6 Universe with Half a Million Galaxies. ApJS, 224, 24
Funder Acknowledgement(s): Kaitlynn Lilly acknowledges support from Research Experience for Undergraduate program at the Institute for Astronomy, University of Hawaii-Manoa funded through NSF grant 6104374.
Faculty Advisor: David Sanders, firstname.lastname@example.org
Role: This research was completed entirely by me under the guidance of both Dr. David Sanders and Connor Auge.