Search Publications
Downflow Motions Associated with Impulsive Nonthermal Emissions Observed in the 2002 July 23 Solar Flare
Shibata, Kazunari; Shimojo, Masumi; Yokoyama, Takaaki +1 more
We present a detailed examination of downflow motions above flare loops observed in the 2002 July 23 flare. The extreme-ultraviolet images obtained with the Transition Region and Coronal Explorer show dark downflow motions (sunward motions) above the postflare loops, not only in the decay phase but also in the impulsive and main phases. We also fo…
A Substantial Population of Red Galaxies at z > 2: Modeling of the Spectral Energy Distributions of an Extended Sample
Wuyts, S.; Daddi, E.; Förster Schreiber, N. M. +12 more
We investigate the nature of the substantial population of high-redshift galaxies with Js-Ks>=2.3 colors recently discovered as part of our Faint Infrared Extragalactic Survey (FIRES). This color cut efficiently isolates galaxies at z>2 with red rest-frame optical colors (``distant red galaxies'' [DRGs]). We select J
The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei, and Stellar Halos
Ferguson, Henry C.; Miller, Bryan W.; Lotz, Jennifer M.
We present the results of a Hubble Space Telescope WFPC2 F555W and F814W survey of 69 dwarf elliptical galaxies (dEs) in the Virgo and Fornax Clusters and Leo Group. The V-I colors of the dE globular clusters, nuclei, and underlying field-star populations are used to trace the dE star formation histories. We find that the dE globular cluster candi…
Observable Properties of the Breakout Model for Coronal Mass Ejections
Lynch, B. J.; MacNeice, P. J.; Antiochos, S. K. +2 more
We compare the ``magnetic breakout'' model for coronal mass ejections (CMEs) with observed general properties of CMEs by analyzing in detail recent high-resolution MHD simulations of a complete breakout CME. The model produces an eruption with a three-part plasma density structure that shows a bright circular rim outlining a dark central cavity in…
A Huge Drop in the X-Ray Luminosity of the Nonactive Galaxy RX J1242.6-1119A, and the First Postflare Spectrum: Testing the Tidal Disruption Scenario
Schartel, Norbert; Komossa, Stefanie; Hasinger, Günther +3 more
In recent years, indirect evidence has emerged suggesting that many nearby nonactive galaxies harbor quiescent supermassive black holes. Knowledge of the frequency of occurrence of black holes, of their masses and spins, is of broad relevance for studying black hole growth and galaxy and active galactic nuclei formation and evolution. It has been …
The Origin of Fe II Emission in Active Galactic Nuclei
Korista, K. T.; Ferland, G. J.; Hamann, F. +2 more
We used a very large set of models of broad emission line region (BELR) clouds in active galactic nuclei to investigate the formation of the observed Fe II emission lines. We show that photoionized BELR clouds cannot produce both the observed shape and observed equivalent width of the 2200-2800 Å Fe II UV bump unless there is considerable velocity…
Stellar Populations and Kinematics of Red Galaxies at z > 2: Implications for the Formation of Massive Galaxies
van Dokkum, Pieter G.; Franx, Marijn; Illingworth, Garth D. +13 more
We recently identified a substantial population of galaxies at z>2 with comparatively red rest-frame optical colors. These distant red galaxies (DRGs) are efficiently selected by the simple observed color criterion Js-Ks>2.3. In this paper we present near-infrared spectroscopy with Keck NIRSPEC of six DRGs with previous…
Candidates of z ~= 5.5-7 Galaxies in the Hubble Space Telescope Ultra Deep Field
Yan, Haojing; Windhorst, Rogier A.
We report results from our z~=5.5-7 galaxy search in the Hubble Space Telescope Ultra Deep Field (UDF). Using the 400 orbit of Advanced Camera for Surveys data, we found 108 plausible 5.5<=z<=6.5 (or z~=6 for short) candidates to mAB(z850)=30.0 mag. The contamination to the sample, due to either image artifacts or known…
Hubble Space Telescope STIS Ultraviolet Spectral Evidence of Outflow in Extreme Narrow-Line Seyfert 1 Galaxies. II. Modeling and Interpretation
Leighly, Karen M.
We present modeling to explore the conditions of the broad-line-emitting gas in two extreme narrow-line Seyfert 1 galaxies, using the observational results described in the first paper of this series. Photoionization modeling using CLOUDY was conducted for the broad blueshifted wind lines and the narrow, symmetric, rest-wavelength-centered disk li…
A Numerical Study of the Breakout Model for Coronal Mass Ejection Initiation
Antiochos, S. K.; Phillips, A.; MacNeice, P. +3 more
A leading theory for the initiation of coronal mass ejections (CMEs) is the breakout model, in which magnetic reconnection above a filament channel is responsible for disrupting the coronal magnetic field. We present the first simulations of the complete breakout process including the initiation, the plasmoid formation and ejection, and the eventu…