Search Publications
Delving Deeper into the Tumultuous Lives of Galactic Dwarfs: Modeling Star Formation Histories
Dolphin, Andrew E.; Skillman, Evan D.; Holtzman, Jon A. +3 more
The paucity of observed dwarf galaxies in the Local Group relative to the abundance of predicted dark matter halos remains one of the greatest puzzles of the ΛCDM paradigm. Solving this puzzle now requires not only matching the numbers of objects but also understanding the details of their star formation histories. We present a summary of such his…
Cooling of the Crust in the Neutron Star Low-Mass X-Ray Binary MXB 1659-29
Miller, Jon M.; Cackett, Edward M.; Wijnands, Rudy +2 more
In quasi-persistent neutron star transients, long outbursts cause the neutron star crust to be heated out of thermal equilibrium with the rest of the star. During quiescence, the crust then cools back down. Such crustal cooling has been observed in two quasi-persistent sources: KS 1731-260 and MXB 1659-29. Here we present an additional Chandra obs…
Radio-Quiet Fast and Wide Coronal Mass Ejections
Kaiser, M. L.; Howard, R. A.; Gopalswamy, N. +5 more
We report on the properties of radio-quiet (RQ) and radio-loud (RL) coronal mass ejections (CMEs) that are fast and wide (FW). RQ CMEs lack type II radio bursts in the metric and decameter-hectometric (DH) wavelengths. RL CMEs are associated with metric or DH type II bursts. We found that ~40% of the FW CMEs from 1996 to 2005 were RQ. The RQ CMEs …
Tracing the Mass-Dependent Star Formation History of Late-Type Galaxies Using X-Ray Emission: Results from the Chandra Deep Fields
Wolf, C.; Lehmer, B. D.; Hornschemeier, A. E. +11 more
We report on the X-ray evolution over the last ≈9 Gyr of cosmic history (i.e., since z = 1.4) of late-type galaxy populations in the Chandra Deep Field-North and Extended Chandra Deep Field-South (CDF-N and E-CDF-S, respectively; jointly CDFs) survey fields. Our late-type galaxy sample consists of 2568 galaxies, which were identified using rest-fr…
The Baryon Content of Dark Matter Halos: Empirical Constraints from Mg II Absorbers
Chen, Hsiao-Wen; Tinker, Jeremy L.
We study the extent and covering fraction of cool baryons around galaxies of different luminosity and mass, based on a survey of Mg II λλ2796, 2803 absorption features near known galaxies. The initial sample consists of 13 galaxy and absorber pairs and 10 galaxies that do not produce Mg II absorption lines to within sensitive upper limits. The red…
Hinode Observations of Magnetic Elements in Internetwork Areas
Lites, B. W.; Ishikawa, R.; Tarbell, T. D. +3 more
We use sequences of images and magnetograms from Hinode to study magnetic elements in internetwork parts of the quiet solar photosphere. Visual inspection shows the existence of many long-lived (several hours) structures that interact frequently and may migrate over distances of ~7 Mm over a period of a few hours. About a fifth of the elements hav…
X-MAS2: Study Systematics on the ICM Metallicity Measurements
Rasia, E.; Bourdin, H.; Mazzotta, P. +5 more
X-ray measurements of the intracluster medium metallicity are becoming more and more frequent due to the availability of powerful X-ray telescopes with excellent spatial and spectral resolutions. The information that can be extracted from measurements of the α-elements, such as oxygen, magnesium, and silicon, with respect to the iron abundance is …
The End of Amnesia: A New Method for Measuring the Metallicity of Type Ia Supernova Progenitors Using Manganese Lines in Supernova Remnants
Hughes, John P.; Badenes, Carles; Bravo, Eduardo
We propose a new method to measure the metallicity of Type Ia supernova progenitors using Mn and Cr lines in the X-ray spectra of young supernova remnants. We show that the Mn-to-Cr mass ratio in Type Ia supernova ejecta is tightly correlated with the initial metallicity of the progenitor, as determined by the neutron excess of the white dwarf mat…
Spectroscopic Detection of Turbulence in Post-CME Current Sheets
Bemporad, A.
Plasma in post-CME current sheets (CSs) is expected to be highly turbulent because of the tearing and coalescence instability and/or local microscopic instabilities. For this reason, in the last decade the inconsistency between the observed (~104-105 km) and the expected (~1-10 m) CS thickness has been tentatively explained i…
Comparison of Distances from RR Lyrae Stars, the Tip of the Red Giant Branch, and Classical Cepheids
Sandage, Allan; Tammann, G. A.; Reindl, B.
The extragalactic distance scale relies heavily on Cepheids. However, it has become clear from observations and pulsation models that the slope and zero point of their P-L relations differ from galaxy to galaxy. This makes the determination of Cepheid distances complex and calls for an independent test of their differences. The test is provided by…