{"id":{"repo_id":"gmu","oai_identifier":"oai:MARS:1920/13762"},"canonical_url":"https://search.dev.ndltd.org/etd/gmu/oai:MARS:1920/13762","repository":{"repo_id":"gmu","name":"George Mason University","base_url":"https://mars.gmu.edu/server/oai/request"},"display":{"title":"It's About Time! A Time-Domain Multi-Wavelength Study of Nearby Active Galactic Nuclei","abstract":"Supermassive black holes (SMBHs) are known to reside at the center of nearly everymajor galaxy, and there is a well-established correlation between the black hole mass and stellar velocity dispersion, indicating a co-evolution between the SMBH and the host galaxy. Gravity alone cannot explain this correlation since the gravitational sphere of influence of the SMBH extends out to only a few parsec, meaning there must be some other mechanism at play. One such mechanism is when gas and dust is accreted onto the SMBH, generating enormous amounts of energy in the form of outflowing winds or collimated jets called active galactic nuclei (AGN). AGNs can produce ’feedback’ on the host galaxy by heating the gas of the surrounding interstellar medium, via radiative and mechanical energy, which in turn can cause quenching of star formation. In the case of mechanical feedback, collimated jets can propagate out to kilo-parsec and even mega-parsec scales. There is still ongoing debate as to the exact driving mechanisms in AGNs that contribute to the launching of jets, as jets are generally inferred to originate very close to the SMBH, in a possibly synchrotron self-absorbed corona. This is a cloud of hot free electrons confined to an area that resides somewhere above the accretion disk where UV photons emitted by the accretion disk are inverse Compton scattered, bumping their energies to the X-ray regime. There have been many relationships, or correlations, between radio and X-ray emission found in the litera- ture, applying to both stellar-sized black holes and SMBHs. One relationship in particular is the so-called ’fundamental plane’, which purports to unify X-ray and radio emission from accreting black holes in general by introducing black hole mass as a third parameter; how- ever, this relationship has recently been shown to break down on the smallest physical scales where it was expected to be strongest. Correlations between the X-ray and radio emission in accreting black holes suggest that the X-ray corona is also the origin of the radio emis- sion, and may also be associated with the launching of jets, but the exact mechanism is still a matter of ongoing research. The X-ray emission can also be used to estimate the bolometric luminosity of the AGN, which is indicative of the accretion rate of the SMBH. With a high enough accretion rate, the AGN becomes radiatively efficient to drive winds and referred to as radiative feedback. Several outstanding questions exist, such as whether or not both the primary radio and X-ray emission of AGNs originate in the corona. If they do have the same origin, are they coupled? Which AGN feedback mechanism is dom- inant in the local universe? A powerful method to address these questions is simultaneous multi-wavelength observations, which include X-ray observations and very long baseline in- terferometery (VLBI) that can resolve radio emission in local AGNs on parsec to sub-parsec scales, providing exquisite views into the inner accretion region. In this PhD dissertation, I make several contributions to our understanding of the different physical mechanisms of ra- dio and X-ray emission in AGNs. This includes finding evidence of anticorrelation between the core radio and X-ray emission and finding the mechanical feedback produced in nearby AGNs may not be as significant as other modes of feedback such as that from radiative feedback. I also include future research in this field that aims to address some remaining questions.","abstract_html":"Supermassive black holes (SMBHs) are known to reside at the center of nearly everymajor galaxy, and there is a well-established correlation between the black hole mass and stellar velocity dispersion, indicating a co-evolution between the SMBH and the host galaxy. Gravity alone cannot explain this correlation since the gravitational sphere of influence of the SMBH extends out to only a few parsec, meaning there must be some other mechanism at play. One such mechanism is when gas and dust is accreted onto the SMBH, generating enormous amounts of energy in the form of outflowing winds or collimated jets called active galactic nuclei (AGN). AGNs can produce ’feedback’ on the host galaxy by heating the gas of the surrounding interstellar medium, via radiative and mechanical energy, which in turn can cause quenching of star formation. In the case of mechanical feedback, collimated jets can propagate out to kilo-parsec and even mega-parsec scales. There is still ongoing debate as to the exact driving mechanisms in AGNs that contribute to the launching of jets, as jets are generally inferred to originate very close to the SMBH, in a possibly synchrotron self-absorbed corona. This is a cloud of hot free electrons confined to an area that resides somewhere above the accretion disk where UV photons emitted by the accretion disk are inverse Compton scattered, bumping their energies to the X-ray regime. There have been many relationships, or correlations, between radio and X-ray emission found in the litera- ture, applying to both stellar-sized black holes and SMBHs. One relationship in particular is the so-called ’fundamental plane’, which purports to unify X-ray and radio emission from accreting black holes in general by introducing black hole mass as a third parameter; how- ever, this relationship has recently been shown to break down on the smallest physical scales where it was expected to be strongest. Correlations between the X-ray and radio emission in accreting black holes suggest that the X-ray corona is also the origin of the radio emis- sion, and may also be associated with the launching of jets, but the exact mechanism is still a matter of ongoing research. The X-ray emission can also be used to estimate the bolometric luminosity of the AGN, which is indicative of the accretion rate of the SMBH. With a high enough accretion rate, the AGN becomes radiatively efficient to drive winds and referred to as radiative feedback. Several outstanding questions exist, such as whether or not both the primary radio and X-ray emission of AGNs originate in the corona. If they do have the same origin, are they coupled? Which AGN feedback mechanism is dom- inant in the local universe? A powerful method to address these questions is simultaneous multi-wavelength observations, which include X-ray observations and very long baseline in- terferometery (VLBI) that can resolve radio emission in local AGNs on parsec to sub-parsec scales, providing exquisite views into the inner accretion region. In this PhD dissertation, I make several contributions to our understanding of the different physical mechanisms of ra- dio and X-ray emission in AGNs. This includes finding evidence of anticorrelation between the core radio and X-ray emission and finding the mechanical feedback produced in nearby AGNs may not be as significant as other modes of feedback such as that from radiative feedback. I also include future research in this field that aims to address some remaining questions.","abstract_has_math":false,"creators":["Fernandez, Luis Christian"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2023,"date_issued":"2023","date_published":"2023","updated_at":"2026-07-27T19:51:56Z","subjects":["active","feedback","radio","time domain","variability","x-ray"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["hdl:1920/13762"],"render_values":[{"text":"hdl:1920/13762","href":null,"code":true}]}]},"links":{"outbound_url":null,"outbound_label":null,"outbound_source":null},"metadata_groups":[{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2023"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["active","feedback","radio","time domain","variability","x-ray"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["hdl:1920/13762"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.other","label":"Dc Description Other","values":["Supermassive black holes (SMBHs) are known to reside at the center of nearly everymajor galaxy, and there is a well-established correlation between the black hole mass and stellar velocity dispersion, indicating a co-evolution between the SMBH and the host galaxy. Gravity alone cannot explain this correlation since the gravitational sphere of influence of the SMBH extends out to only a few parsec, meaning there must be some other mechanism at play. One such mechanism is when gas and dust is accreted onto the SMBH, generating enormous amounts of energy in the form of outflowing winds or collimated jets called active galactic nuclei (AGN). AGNs can produce ’feedback’ on the host galaxy by heating the gas of the surrounding interstellar medium, via radiative and mechanical energy, which in turn can cause quenching of star formation. In the case of mechanical feedback, collimated jets can propagate out to kilo-parsec and even mega-parsec scales. There is still ongoing debate as to the exact driving mechanisms in AGNs that contribute to the launching of jets, as jets are generally inferred to originate very close to the SMBH, in a possibly synchrotron self-absorbed corona. This is a cloud of hot free electrons confined to an area that resides somewhere above the accretion disk where UV photons emitted by the accretion disk are inverse Compton scattered, bumping their energies to the X-ray regime. There have been many relationships, or correlations, between radio and X-ray emission found in the litera- ture, applying to both stellar-sized black holes and SMBHs. One relationship in particular is the so-called ’fundamental plane’, which purports to unify X-ray and radio emission from accreting black holes in general by introducing black hole mass as a third parameter; how- ever, this relationship has recently been shown to break down on the smallest physical scales where it was expected to be strongest. Correlations between the X-ray and radio emission in accreting black holes suggest that the X-ray corona is also the origin of the radio emis- sion, and may also be associated with the launching of jets, but the exact mechanism is still a matter of ongoing research. The X-ray emission can also be used to estimate the bolometric luminosity of the AGN, which is indicative of the accretion rate of the SMBH. With a high enough accretion rate, the AGN becomes radiatively efficient to drive winds and referred to as radiative feedback. Several outstanding questions exist, such as whether or not both the primary radio and X-ray emission of AGNs originate in the corona. If they do have the same origin, are they coupled? Which AGN feedback mechanism is dom- inant in the local universe? A powerful method to address these questions is simultaneous multi-wavelength observations, which include X-ray observations and very long baseline in- terferometery (VLBI) that can resolve radio emission in local AGNs on parsec to sub-parsec scales, providing exquisite views into the inner accretion region. In this PhD dissertation, I make several contributions to our understanding of the different physical mechanisms of ra- dio and X-ray emission in AGNs. This includes finding evidence of anticorrelation between the core radio and X-ray emission and finding the mechanical feedback produced in nearby AGNs may not be as significant as other modes of feedback such as that from radiative feedback. I also include future research in this field that aims to address some remaining questions."]},{"key":"dc:title","label":"Title","values":["It's About Time! A Time-Domain Multi-Wavelength Study of Nearby Active Galactic Nuclei"]}]}],"canonical_facts":{"dc:date.issued":["2023"],"dc:description.other":["Supermassive black holes (SMBHs) are known to reside at the center of nearly everymajor galaxy, and there is a well-established correlation between the black hole mass and stellar velocity dispersion, indicating a co-evolution between the SMBH and the host galaxy. Gravity alone cannot explain this correlation since the gravitational sphere of influence of the SMBH extends out to only a few parsec, meaning there must be some other mechanism at play. One such mechanism is when gas and dust is accreted onto the SMBH, generating enormous amounts of energy in the form of outflowing winds or collimated jets called active galactic nuclei (AGN). AGNs can produce ’feedback’ on the host galaxy by heating the gas of the surrounding interstellar medium, via radiative and mechanical energy, which in turn can cause quenching of star formation. In the case of mechanical feedback, collimated jets can propagate out to kilo-parsec and even mega-parsec scales. There is still ongoing debate as to the exact driving mechanisms in AGNs that contribute to the launching of jets, as jets are generally inferred to originate very close to the SMBH, in a possibly synchrotron self-absorbed corona. This is a cloud of hot free electrons confined to an area that resides somewhere above the accretion disk where UV photons emitted by the accretion disk are inverse Compton scattered, bumping their energies to the X-ray regime. There have been many relationships, or correlations, between radio and X-ray emission found in the litera- ture, applying to both stellar-sized black holes and SMBHs. One relationship in particular is the so-called ’fundamental plane’, which purports to unify X-ray and radio emission from accreting black holes in general by introducing black hole mass as a third parameter; how- ever, this relationship has recently been shown to break down on the smallest physical scales where it was expected to be strongest. Correlations between the X-ray and radio emission in accreting black holes suggest that the X-ray corona is also the origin of the radio emis- sion, and may also be associated with the launching of jets, but the exact mechanism is still a matter of ongoing research. The X-ray emission can also be used to estimate the bolometric luminosity of the AGN, which is indicative of the accretion rate of the SMBH. With a high enough accretion rate, the AGN becomes radiatively efficient to drive winds and referred to as radiative feedback. Several outstanding questions exist, such as whether or not both the primary radio and X-ray emission of AGNs originate in the corona. If they do have the same origin, are they coupled? Which AGN feedback mechanism is dom- inant in the local universe? A powerful method to address these questions is simultaneous multi-wavelength observations, which include X-ray observations and very long baseline in- terferometery (VLBI) that can resolve radio emission in local AGNs on parsec to sub-parsec scales, providing exquisite views into the inner accretion region. In this PhD dissertation, I make several contributions to our understanding of the different physical mechanisms of ra- dio and X-ray emission in AGNs. This includes finding evidence of anticorrelation between the core radio and X-ray emission and finding the mechanical feedback produced in nearby AGNs may not be as significant as other modes of feedback such as that from radiative feedback. I also include future research in this field that aims to address some remaining questions."],"dc:identifier":["hdl:1920/13762"],"dc:subject":["active","feedback","radio","time domain","variability","x-ray"],"dc:title":["It's About Time! A Time-Domain Multi-Wavelength Study of Nearby Active Galactic Nuclei"],"dc:type":["Dissertation"]},"updated_at":"2026-07-27T19:51:56Z"}