Browsing by Author "Kirkpatrick, Allison"
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Item The Accretion History of AGN: A Newly Defined Population of Cold Quasars(2019-08-15) Kirkpatrick, Allison; Urry, C. Megan; Brewster, Jason; Cooke, Kevin C.; Estrada, Michael; Glikman, Eilat; Hamblin, Kurt; Ananna, Tonima Tasnim; Carlile, Casey; Coleman, Brandon; Johnson, Jordan; Kartaltepe, Jeyhan S.; LaMassa, Stephanie M.; Marchesi, Stefano; Powell, Meredith; Sanders, Dave; Treister, Ezequiel; Turner, Tracey JaneQuasars are the most luminous of active galactic nuclei (AGN), and are perhaps responsible for quenching star formation in their hosts. The Stripe 82X catalog covers 31.3 deg² of the Stripe 82 field, of which the 15.6 deg² covered with XMM-Newton is also covered by Herschel/SPIRE. We have 2500 X-ray detected sources with multi-wavelength counterparts, and 30% of these are unobscured quasars, with LX > 10⁴⁴ erg/s and MB < −23. We define a new population of quasars which are unobscured, have X-ray luminosities in excess of 10⁴⁴ erg/s, have broad emission lines, and yet are also bright in the far-infrared, with a 250 µm flux density of S₂₅₀ > 30 mJy. We refer to these Herscheldetected, unobscured quasars as “Cold Quasars”. A mere 4% (23) of the X-ray- and optically-selected unobscured quasars in Stripe 82X are detected at 250 µm. These Cold Quasars lie at z ∼ 1 − 3, have Mdust ∼ 10⁸ −10⁹ M , have LIR > 10¹² L , and have star formation rates of 200−2000 M /yr. Cold Quasars are bluer in the mid-IR than the full quasar population, and 75% of our Cold Quasars have WISE W3 < 11.5 [Vega], while only 19% of the full quasar sample meets this criteria. Crucially, Cold Quasars have 4−7× as much star formation as the unobscured quasar population at similar redshifts. This phase is likely short-lived, as the central engine and immense star formation consume the gas reservoir. Cold Quasars are type-1 blue quasars that reside in starburst galaxies.Item Dying of the Light: An X-ray Fading Cold Quasar at z ~ 0.405(IOP, 2020-11-06) Cooke, Kevin C.; Kirkpatrick, Allison; Estrada, Michael; Messias, Hugo; Peca, Alessandro; Cappelluti, Nico; Ananna, Tonima Tasnim; Brewster, Jason; Glikman, Eilat; LaMassa, Stephanie; Leung, T. K. Daisy; Trump, Jonathan R.; Turner, Tracey Jane; Urry, C. MeganCold quasars are a rare subpopulation observed to host unobscured, X-ray luminous active galactic nuclei (AGN) while also retaining a cold gas supply fueling high star formation rates. These objects are interpreted as AGN early in their evolution. We present new SOFIA HAWC+ far-infrared observations, far-ultraviolet to far-infrared (FUV–FIR) photometry, and optical spectroscopy to characterize the accretion and star formation behavior in a cold quasar at z ~ 0.405 (CQ 4479). CQ 4479 is a starburst galaxy with a predominantly young stellar population and a high gas mass fraction of ~50%–70%. The AGN component has yet to become the dominant component of the FIR emission. We also find AGN bolometric luminosity that varies as a function of observation method and AGN region probed. Finally, we identify a candidate outflow feature corroborating the hypothesis that cold quasars have energetic feedback. This object presents an intriguing look into the early stages of AGN feedback and probes the rare phase where an AGN and cold gaseous component coexist.Item Lower-Luminosity Obscured AGN Host Galaxies are Not Predominantly in Major-Merging Systems at Cosmic Noon(2021-07-15) Lambrides, Erini; Chiaberge, Marco; Heckman, Timothy; Kirkpatrick, Allison; Meyer, Eileen T.; Petric, Andreea; Hall, Kirsten; Long, Arianna; Watts, Duncan J.; Gilli, Roberto; Simons, Raymond; Tchernyshyov, Kirill; Rodriguez-Gomez, Vicente; Vito, Fabio; Vega, Alexander De La; Davis, Jeffrey R.; Kocevski, Dale D.; Norman, ColinFor over 60 years, the scientific community has studied actively growing central super-massive black holes (active galactic nuclei -- AGN) but fundamental questions on their genesis remain unanswered. Numerical simulations and theoretical arguments show that black hole growth occurs during short-lived periods (∼ 10⁷ -10⁸ yr) of powerful accretion. Major mergers are commonly invoked as the most likely dissipative process to trigger the rapid fueling of AGN. If the AGN-merger paradigm is true, we expect galaxy mergers to coincide with black hole accretion during a heavily obscured AGN phase (NH >10²³ cm⁻²). Starting from one of the largest samples of obscured AGN at 0.5 < z < 3.1, we select 40 non-starbursting lower-luminosity obscured AGN. We then construct a one-to-one matched redshift- and near-IR magnitude-matched non-starbursting inactive galaxy control sample. Combining deep color \textit{Hubble Space Telescope} imaging and a novel method of human classification, we test the merger-AGN paradigm prediction that heavily obscured AGN are strongly associated with galaxies undergoing a major merger. On the total sample of 80 galaxies, we estimate each individual classifier's accuracy at identifying merging galaxies/post-merging systems and isolated galaxies. We calculate the probability of each galaxy being in either a major merger or isolated system, given the accuracy of the human classifiers and the individual classifications of each galaxy. We do not find statistically significant evidence that obscured AGN at cosmic noon are predominately found in systems with evidence of significant merging/post-merging features.Item Merger or Not: Accounting for Human Biases in Identifying Galactic Merger Signatures(2021-06-29) Lambrides, Erini; Watts, Duncan J.; Chiaberge, Marco; Tchernyshyov, Kirill; Kirkpatrick, Allison; Meyer, Eileen T.; Heckman, Timothy; Simons, Raymond; Amram, Oz; Hall, Kirsten R.; Long, Arianna; Norman, ColinSignificant galaxy mergers throughout cosmic time play a fundamental role in theories of galaxy evolution. The widespread usage of human classifiers to visually assess whether galaxies are in merging systems remains a fundamental component of many morphology studies. Studies that employ human classifiers usually construct a control sample, and rely on the assumption that the bias introduced by using humans will be evenly applied to all samples. In this work, we test this assumption and develop methods to correct for it. Using the standard binomial statistical methods employed in many morphology studies, we find that the merger fraction, error, and the significance of the difference between two samples are dependent on the intrinsic merger fraction of any given sample. We propose a method of quantifying merger biases of individual human classifiers and incorporate these biases into a full probabilistic model to determine the merger fraction and the probability of an individual galaxy being in a merger. Using 14 simulated human responses and accuracies, we are able to correctly label a galaxy as ''merger'' or ''isolated'' to within 1\% of the truth. Using 14 real human responses on a set of realistic mock galaxy simulation snapshots our model is able to recover the pre-coalesced merger fraction to within 10\%. Our method can not only increase the accuracy of studies probing the merger state of galaxies at cosmic noon, but also can be used to construct more accurate training sets in machine learning studies that use human classified data-sets.