Search

Context. The [CII] 158 {\mu}m far-infrared (FIR) fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). High spectral resolution observations have shown complex structures in the line profiles of the [CII] emission. Aims. Our aim is to determine whether the complex profiles observed in [^{12}CII] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [^{12}CII] and isotopic [^{13}CII] line profiles. Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in M43, Horsehead~PDR, Monoceros~R2, and M17~SW allow for the detection of optically thin [^{13}CII] emission lines, along with the [^{12}CII] emission lines, with a high signal-to-noise ratio. We first derived the [^{12}CII] optical depth and the [CII] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [CII] gas: column density and excitation temperature. Results. We find moderate to high [^{12}CII] optical depths in all four sources and self-absorption of [^{12}CII] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent Av of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [CII] gas, with an equivalent Av ranging up to about 13 mag. Conclusions. The column density of the warm background material requires multiple photon-dominated region (PDR) surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [CII] gas detected in absorption cannot be explained with any known scenario and we can only speculate on its origins, Comment: 40 pages, 49 figures

[13CII] observations in several Galactic sources show that the fine-structure [12CII] emission is often optically thick (the optical depths around 1 to a few). The aim of our study is to test whether this also affects the [12CII] emission from nearby galaxies like the Large Magellanic Cloud (LMC). We observed three star-forming regions in the LMC with upGREAT on board SOFIA at the frequency of the [CII] line. The 4GHz band width covers all three hyperfine lines of [13CII] simultaneously. For the analysis, we combined the [13CII] F=1-0 and F=1-1 hyperfine components, as they do not overlap with the [12CII] line in velocity. Three positions in N159 and N160 show an enhancement of [13CII] compared to the abundance-ratio-scaled [12CII] profile. This is likely due to the [12CII] line being optically thick, supported by the fact that the [13CII] line profile is narrower than [12CII], the enhancement varies with velocity, and the peak velocity of [13CII] matches the [OI] 63um self-absorption. The [12CII] line profile is broader than expected from a simple optical depth broadening of the [13CII] line, supporting the scenario of several PDR components in one beam having varying [12CII] optical depths. The derived [12CII] optical depth at three positions (beam size of 14arcsec, corresponding to 3.4pc) is 1--3, which is similar to values observed in several Galactic sources shown in previous studies. If this also applies to distant galaxies, the [CII] intensity will be underestimated by a factor of approximately 2., 5 pages with 3 figures plus one page appendix with 4 figures, accepted for publication in A&A Letter

We present large-scale submm observations towards the Sgr A Complex covering ~300 arcmin2. These data were obtained in the frame of the HEXGAL Program with the Herschel-HIFI satellite and are complemented with submm observations obtained with the NANTEN2/SMART telescope as part of the NANTEN2/SMART Central Nuclear Zone Survey. The observed species are CO(4-3) observed with the NANTEN2/SMART telescope, and [CI](1-0), [CI](2-1), [NII](1-0), and [CII](3/2-1/2) observed with the Herschel-HIFI satellite. The observations are presented in a 1 km/s spectral resolution and a spatial resolution ranging from 46" to 28". The spectral coverage of the three lower frequency lines is +-200 km/s, while in the two high frequency lines, the upper LSR velocity limit is +94 km/s and +145 km/s for the [NII] and [CII] lines, respectively. The spatial distribution of the emission in all lines is very widespread. The bulk of the CO emission is found towards Galactic latitudes below the Galactic plane, and all the known molecular clouds are identified. Both neutral atomic carbon lines have their brightest emission associated with the +50 km/s cloud. Their spatial distribution at this LSR velocity describes a crescent-shape structure, which is probably the result of interaction with the energetic event (one or several supernovae explosions) that gave origin to the non-thermal Sgr A-East source. The [CII] and [NII] emissions have most of their flux associated with the thermal Arched-Filaments and the H Region and bright spots in [CII] emission towards the Central Nuclear Disk (CND) are detected. Warm Gas at very high (|Vlsr| > 100 km/s) LSR velocities is also detected towards the line of sight to the Sgr A Complex, and it is most probably located outside the region, in the X1 orbits.