Search Publications
The Bulk of the Black Hole Growth Since z ~ 1 Occurs in a Secular Universe: No Major Merger-AGN Connection
Koekemoer, Anton M.; Trump, Jonathan R.; Lisker, Thorsten +21 more
What is the relevance of major mergers and interactions as triggering mechanisms for active galactic nuclei (AGNs) activity? To answer this long-standing question, we analyze 140 XMM-Newton-selected AGN host galaxies and a matched control sample of 1264 inactive galaxies over z ~ 0.3-1.0 and M * < 1011.7 M sun w…
A Comprehensive Spectroscopic Analysis of DB White Dwarfs
Fontaine, G.; Bergeron, P.; Wesemael, F. +9 more
We present a detailed analysis of 108 helium-line (DB) white dwarfs based on model atmosphere fits to high signal-to-noise optical spectroscopy. We derive a mean mass of 0.67 M sun for our sample, with a dispersion of only 0.09 M sun. White dwarfs also showing hydrogen lines, the DBA stars, comprise 44% of our sample, and the…
The ACS Nearby Galaxy Survey Treasury. VIII. The Global Star Formation Histories of 60 Dwarf Galaxies in the Local Volume
McQuinn, Kristen B. W.; Dolphin, Andrew E.; Skillman, Evan D. +11 more
We present uniformly measured star formation histories (SFHs) of 60 nearby (D <~ 4 Mpc) dwarf galaxies based on color-magnitude diagrams of resolved stellar populations from images taken with the Hubble Space Telescope and analyzed as part of the ACS Nearby Galaxy Survey Treasury program (ANGST). This volume-limited sample contains 12 dwarf sph…
The Discovery of Y Dwarfs using Data from the Wide-field Infrared Survey Explorer (WISE)
Cushing, Michael C.; Kirkpatrick, J. Davy; Gelino, Christopher R. +13 more
We present the discovery of seven ultracool brown dwarfs identified with the Wide-field Infrared Survey Explorer (WISE). Near-infrared spectroscopy reveals deep absorption bands of H2O and CH4 that indicate all seven of the brown dwarfs have spectral types later than UGPS J072227.51-054031.2, the latest-type T dwarf currently…
A 100 pc Elliptical and Twisted Ring of Cold and Dense Molecular Clouds Revealed by Herschel Around the Galactic Center
Natoli, P.; Piacentini, F.; Polenta, G. +38 more
Thermal images of cold dust in the Central Molecular Zone of the Milky Way, obtained with the far-infrared cameras on board the Herschel satellite, reveal a ~3 × 107 M sun ring of dense and cold clouds orbiting the Galactic center. Using a simple toy model, an elliptical shape having semi-major axes of 100 and 60 pc is deduce…
Three-year Swift-BAT Survey of Active Galactic Nuclei: Reconciling Theory and Observations?
Greiner, J.; Merloni, A.; Comastri, A. +3 more
It is well accepted that unabsorbed as well as absorbed active galactic nuclei (AGNs) are needed to explain the nature and shape of the Cosmic X-ray background (CXB), even if the fraction of highly absorbed objects (dubbed Compton-thick sources) still substantially escapes detection. We derive and analyze the absorption distribution using a comple…
Probing the Intergalactic Medium/Galaxy Connection. V. On the Origin of Lyα and O VI Absorption at z < 0.2
Prochaska, J. Xavier; Mulchaey, J.; Weiner, B. +2 more
We analyze the association of galaxies with Lyα and O VI absorption, the most commonly detected transitions of the low-z intergalactic medium (IGM), in the fields of 14 quasars with z em = 0.06-0.57. Confirming previous studies, we observe a high covering fraction for Lyα absorption to impact parameter ρ = 300 h -1 72
A Model for the Sources of the Slow Solar Wind
Antiochos, S. K.; Linker, J. A.; Mikić, Z. +2 more
Models for the origin of the slow solar wind must account for two seemingly contradictory observations: the slow wind has the composition of the closed-field corona, implying that it originates from the continuous opening and closing of flux at the boundary between open and closed field. On the other hand, the slow wind also has large angular widt…
Constraints on the Assembly and Dynamics of Galaxies. II. Properties of Kiloparsec-scale Clumps in Rest-frame Optical Emission of z ~ 2 Star-forming Galaxies
Lutz, D.; Förster Schreiber, N. M.; Genzel, R. +11 more
We study the properties of luminous stellar "clumps" identified in deep, high-resolution Hubble Space Telescope NIC2/F160W imaging at 1.6 µm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-…
Extreme Feedback and the Epoch of Reionization: Clues in the Local Universe
Heckman, Timothy M.; Leitherer, Claus; Rich, R. Michael +8 more
The source responsible for reionizing the universe at z>6 remains uncertain. While an energetically adequate population of star-forming galaxies may be in place, it is unknown whether a large enough fraction of their ionizing radiation can escape into the intergalactic medium. Attempts to measure this escape fraction in intensely star-forming g…