Search Publications
Powerful Outflows and Feedback from Active Galactic Nuclei
Pounds, Ken; King, Andrew
Active galactic nuclei (AGNs) represent the growth phases of the supermassive black holes in the center of almost every galaxy. Powerful, highly ionized winds, with velocities â¼0.1-0.2c, are a common feature in X-ray spectra of luminous AGNs, offering a plausible physical origin for the well-known connections between the hole and properties of it…
A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
Sing, David K.; Wheatley, Peter J.; Désert, Jean-Michel +8 more
Exoplanets orbiting close to their parent stars may lose some fraction of their atmospheres because of the extreme irradiation. Atmospheric mass loss primarily affects low-mass exoplanets, leading to the suggestion that hot rocky planets might have begun as Neptune-like, but subsequently lost all of their atmospheres; however, no confident measure…
The Discovery of the First “Changing Look” Quasar: New Insights Into the Physics and Phenomenology of Active Galactic Nucleus
Moran, Edward C.; Myers, Adam D.; Heckman, Timothy M. +6 more
SDSS J015957.64+003310.5 is an X-ray selected, z = 0.31 active galactic nucleus (AGN) from the Stripe 82X survey that transitioned from a Type 1 quasar to a Type 1.9 AGN between 2000 and 2010. This is the most distant AGN, and first quasar, yet observed to have undergone such a dramatic change. We re-observed the source with the double spectrograp…
Calibration of the NuSTAR High-energy Focusing X-ray Telescope.
An, Hongjun; Hailey, Charles J.; Walton, Dominic J. +19 more
We present the calibration of the Nuclear Spectroscopic Telescope Array (NuSTAR) X-ray satellite. We used the Crab as the primary effective area calibrator and constructed a piece-wise linear spline function to modify the vignetting response. The achieved residuals for all off-axis angles and energies, compared to the assumed spectrum, are typical…
Compton-thick Accretion in the Local Universe
Bauer, F. E.; Gandhi, P.; Ricci, C. +3 more
Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes and to play an important role in shaping the observed spectrum of the cosmic X-ray background. Hard X-ray (E > 10 keV) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of…
Obscuration-dependent Evolution of Active Galactic Nuclei
Nandra, Kirpal; Aird, James; Liu, Zhu +9 more
We aim to constrain the evolution of active galactic nuclei (AGNs) as a function of obscuration using an X-ray-selected sample of ~2000 AGNs from a multi-tiered survey including the CDFS, AEGIS-XD, COSMOS, and XMM-XXL fields. The spectra of individual X-ray sources are analyzed using a Bayesian methodology with a physically realistic model to infe…
The first ultraviolet quasar-stacked spectrum at z ≃ 2.4 from WFC3
Vignali, C.; Lusso, E.; Prochaska, J. X. +4 more
The ionizing continuum from active galactic nuclei is fundamental for interpreting their broad emission lines and understanding their impact on the surrounding gas. Furthermore, it provides hints on how matter accretes on to supermassive black holes. Using Hubble Space Telescope's Wide Field Camera 3, we have constructed the first stacked ultravio…
Constraining the Milky Way's Hot Gas Halo with O VII and O VIII Emission Lines
Bregman, Joel N.; Miller, Matthew J.
The Milky Way hosts a hot (≈2 × 106 K), diffuse, gaseous halo based on detections of z = 0 O VII and O VIII absorption lines in quasar spectra and emission lines in blank-sky spectra. Here we improve constraints on the structure of the hot gas halo by fitting a radial model to a much larger sample of O VII and O VIII emission line measu…
Black hole feedback in the luminous quasar PDS 456
Harrison, F. A.; Stern, D.; Behar, E. +17 more
The evolution of galaxies is connected to the growth of supermassive black holes in their centers. During the quasar phase, a huge luminosity is released as matter falls onto the black hole, and radiation-driven winds can transfer most of this energy back to the host galaxy. Over five different epochs, we detected the signatures of a nearly spheri…
Scaling properties of a complete X-ray selected galaxy group sample
Lovisari, L.; Reiprich, T. H.; Schellenberger, G.
Context. Upcoming X-ray surveys like eROSITA require precise calibration between X-ray observables and mass down to the low-mass regime to set tight constraints on the fundamental cosmological parameters. Since an individual mass measurement is only possible for relatively few objects, it is crucial to have reliable and clearly understood scaling …