R. Güsten’s research while affiliated with Max Planck Institute for Radio Astronomy and other places

We present SOFIA/upGREAT velocity-resolved spectral imaging and analysis of the 158 um [C II] spectral line toward the central 80 by 43\,pc region of the Central Molecular Zone of the Galaxy. The field we imaged with 14" (0.6 pc) spatial and 1 km/s spectral resolution contains the Circum-Nuclear Disk (CND) around the central black hole Sgr A*, the neighboring thermal Arched Filaments, the nonthermal filaments of the Radio Arc, and the three luminous central star clusters. [C II] traces emission from the CND's inner edge to material orbiting at a distance of approximately 6 pc. Its velocity field reveals no sign of inflowing material nor interaction with winds from the Sgr A East supernova remnant. Wide-field imaging of the Sgr A region shows multiple circular segments, including the thermal Arched Filaments, that are centered on a region that includes the Quintuplet cluster. We examine the possibility that the Arched Filaments and other large-scale arcs trace transient excitation events from supernova blast waves. Along the Arched Filaments, comparisons among far-IR fine structure lines show changes in ionization state over small scales and that high-excitation lines are systematically shifted in position from the other lines. These also point to transient fast winds that shocked on the surface of the Arches cloud to produce additional local UV radiation to excite the Arched Filaments on a cloud surface illuminated by UV from hot stars.

This paper summarizes all presently available $J_ upp thirco and accompanying co measurements of galaxy centers including new$J$=6-5 thirco and co observations of eleven galaxies with the Atacama Pathfinder EXperiment (APEX) telescope and also$Herschel$high-$J$measurements of both species in five galaxies. The observed$J$=6-5/$J$=1-0 co integrated temperature ratios range from 0.10 to 0.45 in matching beams. Multi-aperture data indicate that the emission of thirco (6-5) is more centrally concentrated than that of co (6-5). The intensities of co (6-5) suggest a correlation with those of$ but not with those of HCN. The new data are essential in refining and constraining the parameters of the observed galaxy center molecular gas in a simple two-phase model to approximate its complex multi-phase structure. In all galaxies except the Seyfert galaxy NGC 1068, high-J emission from the center is dominated by a dense ($n and relatively cool (20-60 K) high-pressure gas. In contrast the low-$J$lines are dominated by low-pressure gas of a moderate density ($n and more elevated temperature (60-150 K) in most galaxies. The three exceptions with significant high-pressure gas contributions to the low-J emission are all associated with active central star formation.

Context. Young early-type HAeBe stars are still embedded in the molecular clouds in which they formed. They illuminate reflection nebulae, which shape the surrounding molecular cloud and may trigger star formation. They are therefore ideal places to search for ongoing star formation activity. Aims. NGC 2023 is illuminated by the Herbig Be star HD 37903. It is the most massive member of a small young cluster with about 30 PMS stars, several of which are Class I objects that still heavily accrete. It might therefore be expected that they might drive molecular outflows. We examined the whole region for outflows. Methods. We analyzed previously published APEX data to search for and characterize the outflows in the NGC 2023 region. This is the first systematic search for molecular outflows in this region. Since the outflows were mapped in several CO transitions, we can determine their properties quite well. Results. We have discovered four molecular outflows in the vicinity of NGC 2023, three of which are associated with Class I objects. MIR-63, a bright mid-infrared and submillimeter Class I source, is a binary with a separation of 2″.4 and drives two bipolar outflows orthogonal to each other. The large southeast–northwest outflow excites the Herbig-Haro flow HH 247. MIR-73, a Class I object, which is also a far-infrared source, drives a pole-on outflow. MIR-62 is a Class II object with strong infrared excess and a luminosity of 7 L ⊙ . It is not detected in the far-infrared. The Class I sources have bolometric luminosities of about 20 L ⊙ or lower, that is, they are all low-mass stars. One other far-infrared source, MIR-75, may have powered an outflow in the past because it now illuminates an egg-shaped cavity. Conclusions. The four outflows are all powered by young stars and are located in the immediate vicinity of NGC 2023. They are at a similar evolutionary stage, which suggests that their formation may have been triggered by the expanding C II region.

Context. Stellar feedback plays a crucial role in star formation and the life cycle of molecular clouds. The intense star formation region 30 Doradus, which is located in the Large Magellanic Cloud (LMC), is a unique target for detailed investigation of stellar feedback owing to the proximity of the hosting galaxy and modern observational capabilities that together allow us to resolve individual molecular clouds – nurseries of star formation. Aims. We study the impact of large-scale feedback on the molecular gas using the new observational data in the ¹² CO(3 − 2) line obtained with the APEX telescope. Methods. Our data cover an unprecedented area of 13.8 sq. deg. of the LMC disc with a spatial resolution of 5 pc and provide an unbiased view of the molecular clouds in the galaxy. Using these data, we located molecular clouds in the disc of the galaxy, estimated their properties, such as the areal number density, relative velocity and separation, width of the line profile, CO line luminosity, size, and virial mass, and compared these properties of the clouds of 30 Doradus with those in the rest of the LMC disc. Results. We find that, compared with the rest of the observed molecular clouds in the LMC disc, those in 30 Doradus show the highest areal number density; they are spatially more clustered, they move faster with respect to each other, and they feature larger linewidths. In parallel, we do not find statistically significant differences in such properties as the CO line luminosity, size, and virial mass between the clouds of 30 Doradus and the rest of the observed field. Conclusions. We interpret our results as signatures of gas dispersal and fragmentation due to high-energy large-scale feedback.

It has long been discussed whether stellar feedback in the form of winds and/or radiation can shred the nascent molecular cloud, thereby controlling the star formation rate. However, directly probing and quantifying the impact of stellar feedback on the neutral gas of the nascent clouds is challenging. We present an investigation of this impact toward the RCW 79 H II region using the ionized carbon line at 158 μm ([C II]) from the FEEDBACK Legacy Survey. We combine this data with information on the dozen ionizing O stars responsible for the evolution of the region, and observe in [C II] for the first time both blue- and redshifted high-velocity gas that reaches velocities of up to 25 km s ⁻¹ relative to the bulk emission of the molecular cloud. This high-velocity gas mostly contains neutral gas, and partly forms a fragmented shell, similar to recently found shells in a few Galactic H II regions. However, this shell does not account for all of the observed neutral high-velocity gas. We also find high-velocity gas streaming out of the nascent cloud through holes, and obtain a range of dynamical timescales below 1.0 Myr for the high-velocity gas that is well below the 2.3 ± 0.5 Myr age of the OB cluster. This suggests a different scenario for the evolution of RCW 79, where the high-velocity gas does not solely stem from a spherical expanding bubble, but also from gas recently ablated at the edge of the turbulent molecular cloud into the surrounding interstellar medium through low-pressure holes or chimneys. The resulting mass ejection rate estimate for the cloud is 0.9–3.5 × 10 ⁻² M ⊙ yr ⁻¹ , which leads to short erosion timescales (< 5 Myr) for the nascent molecular cloud. This finding provides direct observational evidence of rapid molecular cloud dispersal.

We quantified the effects of stellar feedback in RCW 49 by determining the physical conditions in different regions using the [C ii ] 158 μ m and [O i ] 63 μ m observations from SOFIA, the ¹² CO (3–2) observations from APEX, and the H 2 line observations from Spitzer telescopes. Large maps of RCW 49 were observed with the SOFIA and APEX telescopes, while the Spitzer observations were only available toward three small areas. From our qualitative analysis, we found that the H 2 0–0 S (2) emission line probes denser gas compared to the H 2 0–0 S (1) line. In four regions (“northern cloud,” “pillar,” “ridge,” and “shell”), we compared our observations with the updated PDR Toolbox models and derived the integrated far-ultraviolet flux between 6 and 13.6 eV ( G 0 ), H nucleus density ( n ), temperatures, and pressures. We found the ridge to have the highest G 0 (2.4 × 10 ³ Habing units), while the northern cloud has the lowest G 0 (5 × 10 ² Habing units). This is a direct consequence of the location of these regions with respect to the Wd2 cluster. The ridge also has a high density (6.4 × 10 ³ cm ⁻³ ), which is consistent with its ongoing star formation. Among the Spitzer positions, we found the one closest to the Wd2 cluster to be the densest, suggesting an early phase of star formation. Furthermore, the Spitzer position that overlaps with the shell was found to have the highest G 0 , and we expect this to be a result of its proximity to an O9V star.

We quantified the effects of stellar feedback in RCW 49 by determining the physical conditions in different regions using the [CII] 158 $\mu$m and [OI] 63 $\mu$m observations from SOFIA, the $^{12}$CO (3-2) observations from APEX and the H$_2$ line observations from Spitzer telescopes. Large maps of RCW 49 were observed with the SOFIA and APEX telescopes, while the Spitzer observations were only available towards three small areas. From our qualitative analysis, we found that the H$_2$ 0-0 S(2) emission line probes denser gas compared to the H$_2$ 0-0 S(1) line. In four regions ("northern cloud", "pillar", "ridge", and "shell"), we compared our observations with the updated PDR Toolbox models and derived the integrated far-ultraviolet flux between 6-13.6 eV ($G_{\rm 0}$), H nucleus density (n), temperatures and pressures. We found the ridge to have the highest $G_{\rm 0}$ (2.4 $\times$ 10$^3$ Habing units), while the northern cloud has the lowest $G_{\rm 0}$ (5 $\times$ 10$^2$ Habing units). This is a direct consequence of the location of these regions with respect to the Wd2 cluster. The ridge also has a high density (6.4 $\times$ 10$^3$ cm$^{-3}$), which is consistent with its ongoing star formation. Among the Spitzer positions, we found the one closest to the Wd2 cluster to be the densest, suggesting an early phase of star formation. Furthermore, the Spitzer position that overlaps with the shell was found to have the highest $G_{\rm 0}$ and we expect this to be a result of its proximity to an O9V star.

We present [C ii ] 158 μ m and [O i ] 63 μ m observations of the bipolar H ii region RCW 36 in the Vela C molecular cloud, obtained within the SOFIA legacy project FEEDBACK, which is complemented with APEX 12/13 CO (3–2) and Chandra X-ray (0.5–7 keV) data. This shows that the molecular ring, forming the waist of the bipolar nebula, expands with a velocity of 1–1.9 km s ⁻¹ . We also observe an increased line width in the ring, indicating that turbulence is driven by energy injection from the stellar feedback. The bipolar cavity hosts blueshifted expanding [C ii ] shells at 5.2 ± 0.5 ± 0.5 km s ⁻¹ (statistical and systematic uncertainty), which indicates that expansion out of the dense gas happens nonuniformly and that the observed bipolar phase might be relatively short (∼0.2 Myr). The X-ray observations show diffuse emission that traces a hot plasma, created by stellar winds, in and around RCW 36. At least 50% of the stellar wind energy is missing in RCW 36. This is likely due to leakage that is clearing even larger cavities around the bipolar RCW 36 region. Lastly, the cavities host high-velocity wings in [C ii ], which indicates relatively high mass ejection rates (∼5 × 10 ⁻⁴ M ⊙ yr ⁻¹ ). This could be driven by stellar winds and/or radiation but remains difficult to constrain. This local mass ejection, which can remove all mass within 1 pc of RCW 36 in 1–2 Myr, and the large-scale clearing of ambient gas in the Vela C cloud indicate that stellar feedback plays a significant role in suppressing the star formation efficiency.

We present [CII] 158 $\mu$m and [OI] 63 $\mu$m observations of the bipolar HII region RCW 36 in the Vela C molecular cloud, obtained within the SOFIA legacy project FEEDBACK, which is complemented with APEX $^{12/13}$CO(3-2) and Chandra X-ray (0.5-7 keV) data. This shows that the molecular ring, forming the waist of the bipolar nebula, expands with a velocity of 1 - 1.9 km s$^{-1}$. We also observe an increased linewidth in the ring indicating that turbulence is driven by energy injection from the stellar feedback. The bipolar cavity hosts blue-shifted expanding [CII] shells at 5.2$\pm$0.5$\pm$0.5 km s$^{-1}$ (statistical and systematic uncertainty) which indicates that expansion out of the dense gas happens non-uniformly and that the observed bipolar phase might be relatively short ($\sim$0.2 Myr). The X-ray observations show diffuse emission that traces a hot plasma, created by stellar winds, in and around RCW 36. At least 50 \% of the stellar wind energy is missing in RCW 36. This is likely due to leakage which is clearing even larger cavities around the bipolar RCW 36 region. Lastly, the cavities host high-velocity wings in [CII] which indicates relatively high mass ejection rates ($\sim$5$\times$10$^{-4}$ M$_{\odot}$ yr$^{-1}$). This could be driven by stellar winds and/or radiation pressure, but remains difficult to constrain. This local mass ejection, which can remove all mass within 1 pc of RCW 36 in 1-2 Myr, and the large-scale clearing of ambient gas in the Vela C cloud indicates that stellar feedback plays a significant role in suppressing the star formation efficiency (SFE).