Search Publications
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…
Selected Problems in Collisionless-Shock Physics
Krasnoselskikh, V.; Kucharek, H.; Scholer, M. +6 more
The physics of collisionless shocks is a very broad topic, which has been well studied for many decades. However, there are a number of important issues which remain unresolved. Moreover, there have been new findings, which cast doubt on well-established ideas. The purpose of this review is to address a subset of unresolved problems in collisionle…
Mapping ices in protostellar environments on 1000 AU scales. Methanol-rich ice in the envelope of Serpens SMM 4
van Dishoeck, E. F.; Pontoppidan, K. M.; Dartois, E.
We present VLT-ISAAC L-band spectroscopy toward 10 stars in SVS 4, a 30 arcsec×45 arcsec dense cluster of pre-main sequence stars deeply embedded in the Serpens star forming cloud. The ISAAC spectra are combined with archival imaging from UKIRT and ISOCAM to derive accurate extinctions toward the SVS 4 stars. The data are then used to construct a …
Evidence for a multizone warm absorber in the XMM-Newton spectrum of Markarian 304
Guainazzi, M.; Schartel, N.; Rodríguez-Pascual, P. M. +3 more
We present a XMM-Newton observation of Markarian 304, a Seyfert 1 galaxy at z= 0.066. The EPIC data show that MKN 304 is affected by heavy (NH~ 1023 cm-2) obscuration arising from ionized gas. A two-phase warm absorber provides an adequate parametrization of this gas. The ionization parameter of the two components …
XMM-Newton observations of the Perseus cluster - II. Evidence for gas motions in the core
Böhringer, H.; Sunyaev, R.; Churazov, E. +2 more
The 5-9 keV spectrum of the inner ~100 kpc of the Perseus cluster measured by XMM-Newton can be well described by an optically thin plasma emission model as predicted by the APEC code, without any need for invoking a strong Ni overabundance or the effects of resonant scattering. For the strongest 6.7-keV line of He-like iron, the optical depth of …
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…
Surprising Sun: A New Step Towards a Complete Picture?
García, R. A.; Turck-Chièze, S.; Piau, L. +5 more
Important revisions of the solar model ingredients have appeared recently. We first show that the updated CNO composition suppresses the anomalous position of the Sun in the known galactic enrichment. The following law, He/H=0.075+44.6 O/H in number fraction, is now compatible with all the indicators. We then suggest some directions of investigati…