Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-10-27
Mon.Not.Roy.Astron.Soc. 346 (2003) L57
Astronomy and Astrophysics
Astrophysics
5 pages, 6 figures. Accepted for publication in MNRAS (Letters). Minor typos removed to match version in press
Scientific paper
10.1111/j.1365-2966.2003.07333.x
We report high spectral resolution Australia Telescope Compact Array HI 21 cm observations resulting in the detection of the warm neutral medium (WNM) of the Galaxy in absorption against two extragalactic radio sources, PKS 1814-637 and PKS 0407-658. The two lines of sight were selected on the basis of the simplicity of their absorption profiles and the strength of the background sources; the high velocity resolution of the spectra then enabled us to estimate the kinetic temperatures of the absorbing gas by fitting multiple Gaussians to the absorption profiles. Four separate WNM components were detected toward the two sources, with peak optical depths $\tau_{max} = (1.0 \pm 0.08) \times 10^{-2}$, $(1.4 \pm 0.2) \times 10^{-3}$, $(2.2 \pm 0.5) \times 10^{-3}$ and $(3.4 \pm 0.5) \times 10^{-3}$ and kinetic temperatures $T_{k} = 3127 \pm 300$ K, $3694 \pm 1595$ K, $3500 \pm 1354$ K and $2165 \pm 608$ K respectively. All four components were thus found to have temperatures in the thermally unstable range $500 < T_{k} < 5000$ K; this suggests that thermal equilibrium has not been reached throughout the WNM.
Chengalur Jayaram N.
Kanekar Nissim
Safouris Vicky
Subrahmanyan Ravi
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