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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[103.01] The Double Helix Nebula: A Torsional Wave Propagating Along the Galactic Center Magnetic Field?

M.R. Morris (UCLA), K.I. Uchida (Cornell U.), T. Do (UCLA)

With the MIPS camera on the Spitzer Space Telescope we have found at a wavelength of 24 microns an unprecedented infrared nebula having the morphology of an intertwined double helix. This feature is located about 100 pc from the Galaxy’s dynamical center toward positive Galactic latitude, and its axis is oriented perpendicular to the Galactic plane. The observed segment, about 25 pc in length and containing about 1.25 full turns of each of the two continuous, helically wound strands, is part of a much larger structure evident in lower-resolution images previously obtained in the mid-infrared with the MSX satellite. We interpret this feature as a torsional Alfvén wave propagating vertically away from the Galactic disk, driven by rotation of the magnetized circumnuclear disk (CND). As such, it offers a new large-scale morphological probe of the Galactic center magnetic field. The lateral extent of the hypothetical wave is similar to that of the CND, and the wavelength -- 7.5 arcminutes, or 19 pc -- is consistent with the rotation period of the CND and the expected range of possible values of the Alfvén velocity in the low-density interstellar medium of the Galactic center. The direct connection between the circumnuclear disk and the double helix is ambiguous, but the MSX images show a possible meandering channel that warrants further investigation.

This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This research also made use of data products from the Midcourse Space Experiment and made use of the NASA/ IPAC Infrared Science Archive.

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