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Q. D. Wang, S. Immler (Univ. of Massachusetts), R. Walterbos (New Mexico State University), D. Breitschwerdt (Princeton University)
We will present a spectacular Chandra X-ray image of NGC4631. This image shows, unambiguously for the first time, the presence of a giant diffuse X-ray-emitting corona around a disk galaxy. This corona extends as far as 10 kpc away from the plane of NGC4631. The X-ray morphology resembles the radio halo of the galaxy, indicating a close connection among outflows of hot gas, cosmic rays, and magnetic field from the galactic disk. Unlike hot gas outflows observed from circumnuclear regions of several nearby starburst galaxies, the corona of NGC4631 evidently represents the ``smoke'' from numerous ``galactic chimneys'', or filamentary features emanating vertically from the galactic disk, as revealed in our deep HST WFPC2 H\alpha image. While indications of the extraplanar X-ray emission were also present in previous ROSAT observations of NGC4631, the superb sensitivity and spatial resolution of the Chandra image allow us to remove previous confusion with point-like sources and to determine the distribution of hot gas in the corona. Such a corona has been speculated for our Milky Way for more than four decades, but a definitive confirmation is still elusive.
A spatially-resolved spectroscopic analysis of the Chandra observation will further enable us to examine the chemical and thermal properties of the hot gas. This, combined with self-consistent dynamical and plasma emission models, may help us to constrain the dynamics and energy sources/sinks of the corona. The results will have strong implications for our understanding of the feedback from galaxies as well as their structure and evolution.
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