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M. Nord (Naval Research Laboratory)
I present new high angular resolution radio images of the Galactic center at 74 and 330 MHz, which have been used to study the Galactic center itself as well as the Galactic cosmic-ray emissivity.
With a resolution of ~10" and an RMS noise of 1.6 mJy/beam, the 330 MHz image represents a significant increase in resolution and sensitivity over the previously published images at this frequency. The improved sensitivity has more than tripled the census of small diameter sources in the region, has resulted in the detection of two new Non Thermal Filaments (NTFs), 18 NTF candidates, 30 pulsar candidates, reveals previously known extended sources in greater detail, and has resulted in the first detection of Sagittarius A* in this frequency range. These results have offered new insights into our understanding of the Galactic center magnetic field and placed new constraints on the intrinsic emission mechanism from SgrA* itself.
I also present 74 MHz images of the Galactic center and three nearby Galactic plane fields. At low radio frequencies (< 100 MHz), HII regions become opaque (optical depth > 1) and may be observed in absorption against the Galactic non-thermal background. Previous observations of this nature were limited to angular resolutions of several degrees, limiting studies towards a small sample of large HII regions. The 74 MHz system on the VLA is now allowing low frequency observations at spatial resolutions sufficient to detect discrete, well known HII regions towards the inner galaxy. Once the HII regions responsible for the absorption are identified, their previously known distances and electron temperatures can be used to measure the cosmic ray electron synchrotron emissivity along well defined pathlenghts. In turn, these data can be used to develop a unique understanding of the radial profile of the synchrotron emissivity through the Galactic disk, a unique measurement available only to low frequency radio astronomy. Such measurements can provide insights into the acceleration, propagation, and origin of the Galactic cosmic rays.
The Very Large Array of the National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement with Associated Universities, Inc. Basic research in radio astronomy at the Naval Research Laboratory is funded by the Office of Naval Research.
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The author(s) of this abstract have provided an email address for comments about the abstract: Michael.Nord@nrl.navy.mil
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.