http://arxiv.org/abs/1506.01703
We detect emission from [Fe XXI] $\lambda$1354.1, which is a tracer of $10^7$ K gas, in archival HST-COS spectra from the centers of the well-known elliptical galaxies M87 and NGC 4696. The detections are at moderate significance, with S/N of 4.9 and 4.1 respectively. Using this line, we measure the kinematics of the hot gaseous halos in these galaxies, which are stirred by turbulence and bulk flows. The hot gas has a mean velocity which is consistent with zero relative to each galaxy, although in the case of M87 spatial broadening by the off-axis nucleus may be introducing a slight artificial blueshift. In both systems we measure velocity dispersions for this line, which are likely contaminated by spatial broadening. We estimate the effect of spatial broadening and infer turbulent line-of sight velocities of $105^{+28}_{-22}$ km/s and $85^{+22}_{-18}$ km/s, corresponding to turbulent pressures of $7^{+4}_{-3}$% and $5\pm2$% of the total thermal pressure in these respective galaxies. These uncertainties include measurement errors only; the spatial broadening is somewhat uncertain as well so we also provide 90\% upper limits on the turbulent pressure, for which we do not subtract the spatial broadening. These very conservative upper limits are 21% and 17% of the total thermal pressure. We perform emission measure analysis for both sightlines, constraining the characteristic path length and column density of the $\sim10^7$ K gas.
M. Anderson and R. Sunyaev
Fri, 5 Jun 15
27/63
Comments: 11 pages, 4 figures, to be submitted to MNRAS
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