Thesis
Investigating the nature of dual active galactic nuclei in Stripe 82
University of Iowa
Master of Science (MS), University of Iowa
Spring 2019
DOI: 10.17077/etd.7z7y-qqqy
Abstract
<p>During the close approach of two galaxies in a merger, tidally induced gas inflows can trigger simultaneous black hole accretion which are observed as dual active galactic nuclei (dAGNs). Merger simulations predict that the resulting increased nuclear gas reservoirs will obscure the X-ray emissions from the AGNs. We investigate whether dAGNs in mergers are observed to be more obscured than their isolated counterparts by combining the results of previous radio and optical spectroscopy studies with new Chandra X-ray observations for a sample of 4 dAGN systems in the Stripe 82 field. For the 6 detected components, we find the rest-frame X-ray luminosities range between 39.8 < log LX /erg s-1 < 42.0. The sources have redshifts between 0.04 < z < 0.22 and projected separations between 4.3 and 9.2 kpc, as well as multi-wavelength properties most closely resembling low-luminosity AGNs. However, we determine that the X-ray emissions for 2 of the sources likely has strong contributions from hot interstellar medium, and star-formation and X-ray binaries may contribute to the X-ray luminosities of several sources. We do not find evidence of enhanced obscuration through our analysis of X-ray hardness ratios, optical [O III] emission line luminosities, and mid-infrared luminosities. Therefore, we suggest that the unobscured low-level accretion observed for the AGNs in this sample is driven through stochastic processes rather than the massive gas inflows predicted for a merger-driven scenario.</p>
Details
- Title: Subtitle
- Investigating the nature of dual active galactic nuclei in Stripe 82
- Creators
- Arran Connor Gross - University of Iowa
- Contributors
- Hai Fu (Advisor)Cornelia Lang (Committee Member)Philip Kaaret (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Physics
- Date degree season
- Spring 2019
- DOI
- 10.17077/etd.7z7y-qqqy
- Publisher
- University of Iowa
- Number of pages
- xi, 79 pages
- Copyright
- Copyright © 2019 Arran Connor Gross
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 73-79).
- Public Abstract (ETD)
Dual Active Galactic Nuclei (AGN) occur when both black holes at the centers of two merging galaxies are actively accreting material. Simulations predict that AGNs found in galactic mergers will be more luminous and more obscured due to an enhancement of inflowing fuel. We test these predictions using a sample of simultaneously active dual AGNs at close separations in merging galaxies. By comparing the X-ray luminosity with other wavelengths, we find that our sample of objects is faint and resembles low luminosity AGNs. The corresponding accretion rates are low, counter to expectations from merger simulations. We also assess the level of obscuration of the nuclei using the relative amount of absorption of low energy X-rays compared to high energy X-rays. We find that the AGNs in merging galaxies do not show any evidence of enhanced obscuring material along the line of sight. Combining all pieces of evidence, it does not appear that the low-level dual AGNs are being driven by the mergers, but instead are being fueled by small-scale random processes that would normally be expected for isolated galaxies.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9983776640202771
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