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arXiv · 1205.0550

[CII] 158 micron line detection of the warm ionized medium in the Scutum--Crux spiral arm tangency

T. Velusamy·W. D. Langer·J. L. Pineda·P. F. Goldsmith
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Abstract

HIFI GOT C+ Galactic plane [CII] spectral survey has detected strong emission at the spiral arm tangencies. We use the unique viewing geometry of the Scutum-Crux (S-C) tangency near i = 30degs to detect the warm ionized medium (WIM) component traced by [CII] and to study the effects of spiral density waves on Interstellar Medium (ISM) gas. We compare [CII] velocity features with ancillary HI, 12CO and 13CO data near tangent velocities at each longitude to separate the cold neutral medium and the warm neutral + ionized components in the S-C tangency, then we identify [CII] emission at the highest velocities without any contribution from 12CO clouds, as WIM. We present the GOT C+ results for the S-C tangency. We interpret the diffuse and extended excess [CII] emission at and above the tangent velocities as arising in the electron-dominated warm ionized gas in the WIM. We derive an electron density in the range of 0.2 - 0.9 cm^-3 at each longitude, a factor of several higher than the average value from Halpha and pulsar dispersion. We interpret the excess [CII] in S-C tangency as shock compression of the WIM induced by the spiral density waves.

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T. Velusamy, W. D. Langer, J. L. Pineda, P. F. Goldsmith. 2012-05-02. [CII] 158 micron line detection of the warm ionized medium in the Scutum--Crux spiral arm tangency. https://doi.org/10.1051/0004-6361%2F201219303

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