Search Publications
He II Lyβ Gunn-Peterson Absorption: New HST Observations and Theoretical Expectations
Anderson, Scott F.; Pieri, Matthew; Schneider, Donald P. +7 more
Observations of He II Lyα Gunn-Peterson troughs have proved to be a valuable probe of the epoch of helium reionization at z ~ 3. Since this optical depth can become unmeasurably large even for modest He II fractions, various alternate techniques have been proposed to push to higher redshift, and among the more promising is looking at higher-order …
Removal of Titan's Atmospheric Noble Gases by Their Sequestration in Surface Clathrates
Mousis, Olivier; Lunine, Jonathan I.; Mandt, Kathleen E. +3 more
A striking feature of the atmosphere of Titan is that no heavy noble gases other than argon were detected by the Gas Chromatograph Mass Spectrometer aboard the Huygens probe during its descent to Titan's surface in 2005 January. Here we provide an explanation of the mysterious absence or rarity of these noble gases in Titan's atmosphere: the therm…
Radio Evidence of Break-out Reconnection?
Mann, G.; Karlický, M.; Aurass, H. +1 more
We reconsider the 2003 October 28 X17 flare/coronal mass ejection (CME), studying the five minutes immediately before the impulsive flare phase (not discussed in previous work). To this aim we examine complementary dynamic radio spectrograms, single frequency polarimeter records, radio images, space-based longitudinal field magnetograms, and ultra…
Testing Stellar Population Synthesis Models with Sloan Digital Sky Survey Colors of M31's Globular Clusters
Kundu, Arunav; Zepf, Stephen E.; Maccarone, Thomas J. +1 more
Accurate stellar population synthesis models are vital in understanding the properties and formation histories of galaxies. In order to calibrate and test the reliability of these models, they are often compared with observations of star clusters. However, relatively little work has compared these models in the ugriz filters, despite the recent wi…
Constraints on Quasar Lifetimes and Beaming from the He II Lyα Forest
Furlanetto, Steven R.; Lidz, Adam
We show that comparisons of He II Lyα forest lines of sight to nearby quasar populations can strongly constrain the lifetimes and emission geometry of quasars. By comparing the He II and H I Lyα forests along a particular line of sight, one can trace fluctuations in the hardness of the radiation field (which are driven by fluctuations in the He II…
Chandra and ROSAT Observations of A194: Detection of an X-Ray Cavity and Mapping the Dynamics of the Cluster
Baum, Stefi A.; O'Dea, Christopher P.; Churazov, Eugene +6 more
Based on Chandra and ROSAT observations, we investigated the nearby poor cluster A194, which hosts two luminous radio galaxies, NGC 547 (3C 40B) and NGC 541 (3C 40A). We demonstrated the presence of a large X-ray cavity (r ~ 34 kpc) formed by the giant southern radio lobe arising from 3C 40B in NGC 547. The estimated age of the cavity is t = 7.9 ×…
Unveiling Extragalactic Star Formation Using Radio Recombination Lines: An Expanded Very Large Array Pilot Study with NGC 253
Johnson, Kelsey E.; Chomiuk, Laura; Pisano, D. J. +3 more
Radio recombination lines (RRLs) are powerful, extinction-free diagnostics of the ionized gas in young, star-forming regions. Unfortunately, these lines are difficult to detect in external galaxies. We present the results of Expanded Very Large Array (EVLA) observations of the RRL and radio continuum emission at 33 GHz from NGC 253, a nearby nucle…
The Remarkable γ-Ray Activity in the Gravitationally Lensed Blazar PKS 1830-211
Costa, E.; Barbiellini, G.; Longo, F. +34 more
We report the extraordinary γ-ray activity (E > 100 MeV) of the gravitationally lensed blazar PKS 1830-211 (z = 2.507) detected by AGILE between 2010 October and November. On October 14, the source experienced a factor of ~12 flux increase with respect to its average value and remained brightest at this flux level (~500 × 10-8 photon…
A Jet Model for the Broadband Spectrum Of the Seyfert 1 Galaxy NGC 4051
Miller, Jon M.; Markoff, Sera; Maitra, Dipankar +1 more
Recent radio very long baseline interferometry observations of the ~ parsec-scale nuclear region of the narrow line Seyfert 1 galaxy NGC 4051 hint toward the presence of outflowing plasma. From available literature we have collected high-quality, high-resolution broadband spectral energy distribution (SED) data of the nuclear region of NGC 4051 sp…
A High Spatial Resolution Study of the λ = 3 mm Continuum of Orion-KL
Friedel, D. N.; Widicus Weaver, S. L.
Recent interferometric observations have called into question the traditional view of the Orion-KL region, which displays one of the most well-defined cases of chemical differentiation in a star-forming region. Previous lower-resolution images of Orion-KL show emission signatures for oxygen-bearing organic molecules toward the Orion Compact Ridge …