Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models. (arXiv:1212.0541v1 [astro-ph.CO])

Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models. (arXiv:1212.0541v1 [astro-ph.CO]):
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)