Open AccessThe temperature of the warm neutral medium in the Milky Way
Author(s) -
Kanekar Nissim,
Subrahmanyan Ravi,
Chengalur Jayaram N,
Safouris Vicky
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2003.07333.x
Subject(s) - physics , milky way , astrophysics , mean kinetic temperature , spectral line , absorption (acoustics) , galaxy , kinetic energy , telescope , absorption spectroscopy , spectral resolution , thermal , astronomy , optics , thermodynamics , quantum mechanics
We report high‐spectral‐resolution Australia Telescope Compact Array (ATCA) H i 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 towards the two sources, with peak optical depths τ max = (1.0 ± 0.08) × 10 −2 , (1.4 ± 0.2) × 10 −3 , (2.2 ± 0.5) × 10 −3 and (3.4 ± 0.5) × 10 −3 and kinetic temperatures T k = 3127 ± 300, 3694 ± 1595, 3500 ± 1354 and 2165 ± 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.