Limits on the Temperature and Filling Factor of the Warm Ionized Medium Towards the Galactic Centre
We have detected a hydrogen recombination line, near 145 MHz, in the direction of the galactic centre with an optical depth of -2.7 ± 0.3 × 10-4. This is shown to arise in a nearby HII region with an electron density of 7 cm-3. The absence of any significant contribution to this line from the warm ionized medium (WIM) implies that it must have a temperature > 6700K and a filling factor >25%. If the temperature of the WIM is 8000K, then it must have a filling factor >60%.
KeywordsOptical Depth Filling Factor Galactic Centre Recombination Line Average Electron Density
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