Constraints on turbulent pressure in the X-ray halos of giant elliptical
  galaxies from resonant scattering
  The dense cores of X-ray emitting gaseous halos of large elliptical galaxies
with temperatures below about 0.8 keV show two prominent Fe XVII emission
features, which provide a sensitive diagnostic tool to measure the effects of
resonant scattering. We present here high-resolution spectra of five bright
nearby elliptical galaxies, obtained with the Reflection Grating Spectrometers
(RGS) on the XMM-Newton satellite. The spectra for the cores of four of the
galaxies show the Fe XVII line at 15.01 Angstrom being suppressed by resonant
scattering. The data for NGC 4636 in particular allow the effects of resonant
scattering to be studied in detail and to prove that the 15.01 Angstrom line is
suppressed only in the dense core and not in the surrounding regions. Using
deprojected density and temperature profiles for this galaxy obtained with the
Chandra satellite, we model the radial intensity profiles of the strongest
resonance lines, accounting for the effects of resonant scattering, for
different values of the characteristic turbulent velocity. Comparing the model
to the data, we find that the isotropic turbulent velocities on spatial scales
smaller than about 1 kpc are less than 100 km/s and the turbulent pressure
support in the galaxy core is smaller than 5% of the thermal pressure at the
90% confidence level, and less than 20% at 95% confidence. Neglecting the
effects of resonant scattering in spectral fitting of the inner 2 kpc core of
NGC 4636 will lead to underestimates of the chemical abundances of Fe and O by
~10-20%.
