Akos Bogdan, William R. Forman, Mark Vogelsberger, Herve Bourdin, Debora Sijacki, Pasquale Mazzotta, Ralph P. Kraft, Christine Jones, Marat Gilfanov, Eugene Churazov, Laurence P. David
Luminous X-ray gas coronae in the dark matter halos of massive spiral galaxies are a fundamental prediction of structure formation models, yet such coronae remained essentially unexplored. In this paper, for the very first time, we detect and characterize extended hot X-ray coronae beyond the optical disks of two normal massive spiral galaxies, NGC1961 and NGC6753. Based on XMM-Newton X-ray observations, we detect hot gaseous emission extending out to ~60 kpc around both galaxies - well beyond their optical radii. The hot gas, whose best-fit temperature is kT~0.6 keV and abundance is ~0.1 Solar, appears to have a fairly uniform distribution, hinting that the quasi-static gas resides in hydrostatic equilibrium in the potential well of the galaxies. The bolometric luminosity of the hot gas in the (0.05-0.15)r_200 region, where r_200 is the virial radius, is ~6e40 erg/s for both NGC1961 and NGC6753. We derive the baryon mass fractions of NGC1961 and NGC6753 and obtain f_b~0.1, which values fall short of the cosmic baryon fraction. The detected X-ray coronae around NGC1961 and NGC6753 offer an excellent basis to probe structure formation simulations. To this end, the observations are confronted with the recently developed moving mesh code AREPO and the traditionally used smoothed particle hydrodynamics code GADGET. The implemented subresolution physics and the gravity solver are identical in the two codes, but they use different methods to solve the hydrodynamical equations. We conclude that, while neither model gives a perfect description, the observed luminosities, gas masses, and abundances favor the AREPO code. Moreover, the shape of the observed density profiles are also well reproduced by AREPO within ~0.4r_200. However, neither model incorporates efficient feedback from supermassive black holes or supernovae, which could alter the simulated properties of the X-ray coronae. (abridged)
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http://arxiv.org/abs/1212.0541
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