Browsing by Subject "quasars"
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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 Disentangling the AGN and star-formation contributions to the radio-X-ray emission of radio-loud quasars at 1(2020-11-11) Azadi, Mojegan; Wilkes, Belinda; Kuraszkiewicz, Joanna; McDowell, Jonathan; Siebenmorgen, Ralf; Ashby, Matthew; Birkinshaw, Mark; Worrall, Diana; Abrams, Natasha; Barthel, Peter; Fazio, Giovanni; Haas, Martin; Hyman, Sóley; Martínez-Galarza, Rafael; Meyer, EileenTo constrain the emission mechanisms responsible for generating the energy powering the active galactic nuclei (AGN) and their host galaxies, it is essential to disentangle the contributions from both as a function of wavelength. Here we introduce a state-of-the-art AGN radio-to-X-ray spectral energy distribution fitting model (ARXSED). ARXSED uses multiple components to replicate the emission from the AGN and their hosts. At radio wavelengths, ARXSED accounts for radiation from the radio structures (e.g., lobes,jets). At near-infrared to far-infrared wavelengths, ARXSED combines a clumpy medium and a homogeneous disk to account for the radiation from the torus. At the optical-UV and X-ray, ARXSED accounts for the emission from the accretion disk. An underlying component from radio to UV wavelengths accounts for the emission from the host galaxy. Here we present the results of ARXSED fits to the panchromatic SEDs of 20 radio-loud quasars from the 3CRR sample at 170%) to the submm luminosity in half the sample, impacting the submm-based star formation rate estimates. We present the median intrinsic SED of the radio-loud quasars at z>1 and find that the median SED of \cite{Elvis1994} is unable to describe the SED of the radio-selected AGN at z>1. The AGN torus and accretion disk parameters inferred from our fitting technique agree with those in the literature for similar samples. We find that the orientation of the torus/accretion disk does not line up with the inclination of the radio jets in our sample.Item A MULTIZONE MODEL FOR SIMULATING THE HIGH-ENERGY VARIABILITY OF TeV BLAZARS(The American Astronomical Society, 2008-08-12) Graff, Philip B.; Georganopoulos, Markos; Perlman, Eric S.; Kazanas, DemosthenesWe present a time-dependent multizone code for simulating the variability of synchrotron self-Compton (SSC) sources. The code adopts a multizone pipe geometry for the emission region, appropriate for simulating emission from a standing or propagating shock in a collimated jet. Variations in the injection of relativistic electrons in the inlet propagate along the length of the pipe, cooling radiatively. Our code for the first time takes into account the nonlocal, time-retarded nature of SSC losses that are thought to be dominant in TeV blazars. The observed synchrotron and SSC emission is followed self-consistently, taking into account light-travel time delays. At any given time, the emitting portion of the pipe depends on the frequency and the nature of the variation followed. Our simulation employs only one additional physical parameter relative to one-zone models, that of the pipe length, and is computationally very efficient, using simplified expressions for the SSC processes. The code will be useful for observers modeling Fermi, TeV, and X-ray observations of SSC blazars.Item Spectral Properties of Populations Behind the Coherence in Spitzer Near-infrared and Chandra X-Ray Backgrounds(The American Astronomical Society, 2019-09-20) Li, Yanxia; Cappelluti, Nico; Hasinger, Günther; Arendt, Richard; Kashlinsky, Alexander; Pacucci, FabioWe study the coherence of the near-infrared and X-ray background fluctuations and the X-ray spectral properties of the sources producing it. We use data from multiple Spitzer and Chandra surveys, including the UDS/SXDF surveys, the Hubble Deep Field North, the EGS/AEGIS field, the Chandra Deep Field South, and the COSMOS surveys, comprising ∼2275 Spitzer/IRAC hours and ∼16 Ms of Chandra data collected over a total area of ∼1 deg². We report an overall ∼5σ detection of a cross-power signal on large angular scales >20″ between the 3.6 and 4.5 μm and the X-ray bands, with the IR versus [1–2] keV signal detected at 5.2σ. The [0.5–1] and [2–4] keV bands are correlated with the infrared wavelengths at a ∼1–3σ significance level. The hardest X-ray band ([4–7] keV) alone is not significantly correlated with any infrared wavelengths due to poor photon and sampling statistics. We study the X-ray spectral energy distribution of the cross-power signal. We find that its shape is consistent with a variety of source populations of accreting compact objects, such as local unabsorbed active galactic nuclei or high-z absorbed sources. We cannot exclude that the excess fluctuations are produced by more than one population. Because of poor statistics, the current relatively broad photometric bands employed here do not allow distinguishing the exact nature of these compact objects or if a fraction of the fluctuations have instead a local origin.