AAS 207th Meeting, 8-12 January 2006
Session 103 Galactic Center Activity
Oral, Tuesday, 2:00-3:30pm, January 10, 2006, Balcony A

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[103.05] A Study of the Galacic Center Lobe

C. J. Law (Northwestern University)

The Galactic center lobe (GCL) is a degree-scale (140 pc, assuming 8 kpc distance) shell that runs perpendicular away from the galactic plane at radio wavelengths. The GCL spans a region of the Galaxy that is home to a massive black hole, dense star clusters, supernova remnants, and massive star formation. Since it was discovered more than two decades ago, its coincidence with the Galactic center region has led to speculation that it may be a signature of mild starburst- or AGN-fuelled activity; evidence supporting the outflow hypothesis has been weak or contradictory. To further our understanding of the GCL, we have made the following observations of diffuse gas and dust using the GBT, VLA, and \emph{Spitzer/IRAC}:

\begin{enumerate} \item A multi-wavelength radio continuum survey using the GBT shows that the GCL has a nonthermal spectral index that steepens at high Galactic latitudes.

\item A radio recombination line study of the GCL also finds thermal gas within the GCL with line widths that constrain the electron temperature to be less than ~3000 K, but with radial velocities near 0 km s-1.

\item A linearly polarized radio continuum study using the VLA shows that the rotation measure in the GCL ranges from --800 to +400 rad m-2 with an unusual east-west gradient.

\item The warm dust and PAH emission, studied with \emph{Spitzer/IRAC}, is concentrated outside the radio continuum shell. \end{enumerate}

We conclude that the GCL has a single origin and discuss the possibility that it was formed by the expulsion of gas from the Galactic center by stellar winds and supernovae during the last 10 Myr. We also present serendipitous discoveries from the large-area, multiwavelength observing campaign.

This work was made possible by support from the NRAO.

The author(s) of this abstract have provided an email address for comments about the abstract: claw@northwestern.edu

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