Ionized gas towards galactic centre — Constraints from low-frequency recombination lines |
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| Authors: | K R Anantharamaiah D Bhattacharya |
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| Institution: | (1) Rahman Research Institute, 560080 Bangalore;(2) Joint Astronomy Program, Department of Physics, Indian Institute of Science, 560012 Bangalore;(3) Present address: National Radio Astronomy Observatory, VLA, P. O. Box 0, 87801 Socorro, New Mexico, USA |
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| Abstract: | Observations of the H272α recombination line towards the galactic centre show features near VLSR= 0, −50 and + 36 kms−1. We have combined the parameters of these features with the available H166α measurements to obtain the properties of the
ionized gas present along the line of sight and also in the ‘3 kpc arm’. For the line-of-sight ionized gas we get an electron
density around 7 cm−3 and a pathlength through it ∼ 10–60 pc. The emission measure and the electron temperature are in the range 500–2900 pc cm−6 and 2000–6000 K. respectively. The ionized gas in the 3 kpc arm has an electron density of 30 cm−3 and extends over 9 pc along the line of sight if we assume an electron temperature of 104 K. Using the available upper limit to the intensity of the H351α recombination line, we show that the distributed ionized
gas responsible for the dispersion of pulsar signals should have a temperature >4500 K. and a minimum filling factor of 20
per cent. We also show that recombination lines from the ‘warm ionized’ gas proposed by McKee & Ostriker (1977) should be
detectable in the frequency range 100–150 MHz towards the galactic centre with the sensitivity available at present. |
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| Keywords: | galactic centre recombination lines— Galaxy 3 kpc arm-interstellar medium distributed ionized gas |
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