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Diffuse Emission (diffuse + emission)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Polarized diffuse emission at 2.3 GHz in a high Galactic latitude area

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2005
E. Carretti
ABSTRACT Polarized diffuse emission observations at 2.3 GHz in a high Galactic latitude area are presented. The 2°× 2° field, centred at (,= 5h, ,=,49°), is located in the region observed by the BOOMERanG experiment. Our observations were carried out with the Parkes radio telescope, and represent the highest frequency detection to date in a low-emission area. Because of the weaker Faraday rotation effect, the high frequency allows an estimate of the Galactic synchrotron contamination of the cosmic microwave background polarization (CMBP) which is more reliable than that achieved at 1.4 GHz. We find that the angular power spectra of the E - and B -modes have slopes of ,E=,1.46 ± 0.14 and ,B=,1.87 ± 0.22, indicating a flattening with respect to 1.4 GHz. Extrapolated up to 32 GHz, the E -mode spectrum is about three orders of magnitude lower than that of the CMBP, allowing a clean detection even at this frequency. The best improvement concerns the B -mode, for which our single-dish observations provide the first estimate of the contamination on angular scales close to the CMBP peak (about 2°). We find that the CMBP B -mode should be stronger than the synchrotron contamination at 90 GHz for models with tensor-to-scalar perturbation ratio T/S > 0.01. This low level could move down to 60,70 GHz the optimal window for CMBP measurements. [source]

X-rays from the HII Regions and Molecular Clouds near the Galactic Center

ASTRONOMISCHE NACHRICHTEN, Issue S1 2003
Katsuji Koyama
Abstract We report measurements by Chandra of a variety of X-ray sources in the molecular clouds and HII regions of the Sgr B2, Arches, Quintuplet and the Galactic center clusters. Moderately bright X-ray sources are present in the Sgr B2, Quintuplet and the Galactic center clusters at the positions of ultra compact HII regions and bright infrared sources. Their X-ray spectra are fitted with models of a thin thermal plasma with 2,10 keV temperatures and luminosities of ,1032,33erg s,1. The X-ray properties are typical of those of high-mass young stellar objects or clusters of such objects. The Arches Cluster has three bright X-ray sources, at the positions of bright IR and radio stars, with X-ray luminosities of a few ×1033 erg s,1 each, which may indicate an unusual X-ray emission mechanism from high mass YSOs. A unique X-ray feature of molecular clouds and HII regions near the Galactic center is the presence of diffuse emission with a strong 6.4 keV line; in Sgr B2 this is attributable to the fluorescence of gas irradiated by external sources in the Galactic center, while the diffuse emission from Arches is puzzling. [source]

On the Chandra Detection of Diffuse X-Ray Emission from Sgr A*

ASTRONOMISCHE NACHRICHTEN, Issue S1 2003
M. E. Pessah
Abstract Kinematic studies of the stellar motions near Sgr A* have revealed the presence of several million solar masses of dark matter enclosed within 0.015 parsecs of the Galactic Center. However, it is not yet clear what fraction of this material is contained within a single point-like object, as opposed to an extended distribution of orbiting matter (e.g., in the form of neutron stars). Recent Chandra observations suggest that the X-ray emission from this source is partially diffuse. This result provides an important clue that can be used to set some constraints on the mass distribution surrounding the black hole. Here, we develop a simple model in which the diffuse emission is produced by a halo of neutron stars accreting from the gas falling toward the center. We discuss the various accretion mechanisms that are likely to contribute significantly to the X-ray flux, and show that a highly magnetized fraction of old neutron stars may account for the diffuse high-energy source. If this picture is correct, the upper bound to the mass of the central black hole is ,2.2 × 106M,. The core radius of the dark cluster must then be ,0.06 pc. We also discuss the sensitivity of our results to the various assumptions made in our calculations. [source]

Mid-Infrared Imaging and Spectroscopic Observations of the Galactic Center with Subaru/COMICS

ASTRONOMISCHE NACHRICHTEN, Issue S1 2003
Y. Okada
Abstract We report the results of mid-infrared (7.8,m,13.2 ,m) high-spatial resolution imaging and spectroscopic observations of the Galactic center region with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru telescope. The images clearly show bright infrared sources and small structures in the diffuse emission. The spectra of all the observed positions show the 9.7 ,m silicate absorption feature. After corrected for the empirically-derived extinction, the intrinsic spectra of the infrared sources show either strong silicate emission or absorption, while the intrinsic diffuse emission has a power-law type spectrum. This difference indicates a possibility of dust processing due to the interaction between the infrared sources and their surrounding medium or a different origin of the dust grains surrounding the sources from those in the diffuse region. [source]

A Chandra survey of nearby spiral galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 1-2 2003
R.E. Kilgard
Abstract We present results from a Chandra survey of 11 nearby, face-on spiral galaxies. 24 observations totalling 900 ks of new and archival Chandra data reveal more than 1000 X-ray point sources associated with the galaxies, diffuse emission, and hundreds of serendipitous sources. We discuss source populations and luminosity functions and show that the slope of the X-ray luminosity function is correlated with the star formation rate in the galaxies. We also discuss ultraluminous X-ray sources in comparison with sources within the Milky Way. Finally, we discuss ongoing work on source classification based upon X-ray colors and spectra, position within the host galaxies, and multiwavelenth counterparts. [source]