SIMBAD references

The [CII] emission is an important probe of star formation in the Galaxy and in external galaxies. The GOT C+ survey and its follow up observations of spectrally resolved 1.9THz [CII] emission using Herschel HIFI provides the data needed to quantify the Galactic interstellar [CII] gas components as tracers of star formation. We determine the source of the diffuse [CII] emission by studying its spatial (radial and vertical) distributions by separating and evaluating the fractions of [CII] and CO emissions in the Galactic ISM gas components. We used the HIFI [CII] Galactic survey (GOT C+), along with ancillary HI, ¹²CO, ¹³CO, and C¹⁸O data toward 354 lines of sight, and several HIFI [CII] and [CI] position-velocity maps. We quantified the emission in each spectral line profile by evaluating the intensities in 3km/s wide velocity bins, ``spaxels''. Using the detection of [CII] with CO or [CI], we separated the dense and diffuse gas components. We derived 2D Galactic disk maps using the spaxel velocities for kinematic distances. We separated the warm and cold H₂ gases by comparing CO emissions with and without associated [CII]. We find evidence of widespread diffuse [CII] emission with a z-scale distribution larger than that for the total [CII] or CO. The diffuse [CII] emission consists of (i) diffuse molecular (CO-faint) H₂ clouds and (ii) diffuse HI clouds and/or WIM. In the inner Galaxy we find a lack of [CII] detections in a majority (∼62%) of HI spaxels and show that the diffuse component primarily comes from the WIM (∼21%) and that the HI gas is not a major contributor to the diffuse component (∼6%). The warm-H₂ radial profile shows an excess in the range 4 to 7kpc, consistent with enhanced star formation there. We derive, for the first time, the 2D [CII] spatial distribution in the plane and the z-distributions of the individual [CII] gas component. From the GOT C+ detections we estimate the fractional [CII] emission tracing (i) H₂ gas in dense and diffuse molecular clouds as ∼48% and ∼14%, respectively, (ii) in the HI gas ∼18%, and (iii) in the WIM ∼21%. Including non-detections from HI increases the [CII] in HI to ∼27%. The z-scale distributions FWHM from smallest to largest are [CII] sources with CO, ∼130pc, (CO-faint) diffuse H₂ gas, ∼200pc, and the diffuse HI and WIM, ∼330pc. When combined with [CII], CO observations probe the warm-H₂ gas, tracing star formation.