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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.
This article reviews observations and models of the diffuse ionized gas that permeates the disk and halo of our Galaxy and others. It was inspired by a series of invited talks presented during an afternoon scientific session of the 65th birthday cele
The [CII] fine structure transition at 158 microns is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through meter wavelengths. With the advent of ALMA and NOEMA, capable
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We report the discovery of only the fourth massive WO star to be found in the Milky Way, and only the seventh identified within the Local Group. This has resulted from the first observations made in a programme of follow-up spectroscopy of candidate