Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21812907s&link_type=abstract
American Astronomical Society, AAS Meeting #218, #129.07; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
High velocity clouds (HVCs) have been observed in a variety of wavebands, from radio to ultraviolet. Even excess X-rays have been reported near some HVCs. Here, we examine possible production scenarios for the HVC-induced X-rays. Using detailed hydrodynamic and magnetohydrodynamic simulations of HVCs interacting with environmental gas, we examine two scenarios. In the first, the clouds travel fast enough to shock-heat warm environmental gas. In the second, the clouds travel through and mix with hot ambient gas. The X-ray productivity of the first scenario depends strongly on the radiative cooling rate. If it is quenched, then the shock-heated ambient gas is X-ray emissive, producing bright X-rays in the 1/4 keV band and some X-rays in the 3/4 keV band from O VII ions. If, in contrast, the radiative cooling rate is similar to that of collisional ionizational equilibrium plasma with solar abundances, then the shocked gas quickly cools and becomes X-ray dim. The mixed gas in the second scenario is X-ray dim. Only when the cloud moves fast enough to shock-heat the ambient medium and radiative cooling is quenched do we see noticeable fluxes of X-rays. We present the predicted 1/4 keV countrates, O VII intensities, and O VII column densities for comparison with observations. We acknowledge the Chandra Theory Program for funding.
Henley David
Kwak Kyujin
Shelton Robin L.
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