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T. S. Statler, S. Diehl (Ohio University)
Elliptical galaxies are renowned for the correlation among their stellar properties known as the Fundamental Plane. All normal ellipticals are found on or near this two-dimensional locus in the three-dimensional space of optical half-light radius, mean surface brightness, and central stellar velocity dispersion. The Fundamental Plane is understood to be mostly a consequence of the Virial Theorem, which relates the total system mass to its characteristic radius and dispersion, modified somewhat by the not-quite-homologous structure and not-quite-constant mass-to-light ratios of galaxies of different mass.
Through a homogeneous analysis of Chandra X-Ray Observatory archival data for ~ 50 normal ellipticals, we find that there is an analogous Fundamental Plane relation for the hot, X-ray emitting, interstellar gas. The X-ray half-light radii, R, surface brightnesses, I, and gas temperatures T are linked; very roughly, the product IR scales as a steep power (5 to 10) of T. This is different from a simple correlation between X-ray luminosity and temperature.
An X-ray Gas Fundamental Plane (XGFP) would not be an expected consequence of the Virial Theorem because the gas, unlike the stars, is not even weakly self-gravitating. The XGFP is consistent with, but is neither necessary nor sufficient for, hydrostatic equilibrium. Additional intrinsic correlations between the gas temperature, density, and total system mass are needed to create this correlation. We will discuss the implications of the XGFP for galactic wind models, AGN heating, and the purported "entropy floor" of galaxy groups.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.