M. A. Requena-Torres

The chemical and energetic conditions created by radiative feedback are probed with observations of multiple molecular transitions toward M17 SW. Extensive maps, including the 12CO J = 16 → 15, J = 12 → 11, and J = 11 → 10 lines, as well as the HCN J = 8 → 7 and HCO+ J = 9 → 8 transitions, were obtained with the dual band receiver GREAT on board the SOFIA airborne telescope, and with the ground based APEX and IRAM 30 m telescopes. These data provide extensive line spectral energy distributions (LSEDs) of the CO, HCN and HCO+ molecules (and their isotopologues). The excitation conditions of the three species are estimated simultaneously using the same density and temperature in a two-phase non-LTE radiative transfer model of the LSEDs.

The BD+40°4124 region was observed with high angular and spectral resolution with the German heterodyne instrument GREAT in CO J = 13 → 12 and [C ii] on SOFIA. These observations show that the [C ii] emission is very strong in the reflection nebula surrounding the young Herbig Ae/Be star BD+40°4124. A strip map over the nebula shows that the [C ii] emission approximately coincides with the optical nebulosity. The strongest [C ii] emission is centered on the B2 star and a deep spectrum shows that it has faint wings, which suggests that the ionized gas is expanding. We also see faint CO J = 13 → 12 at the position of BD+40°4124, which suggests that the star may still be surrounded by an accretion disk. We also detected [C ii] emission and strong CO J = 13 → 12 toward V 1318 Cyg. Here the [C i] emission is fainter than in BD+40°4124 and appears to come from the outflow, since it shows red and blue wings with very little emission at the systemic velocity, where the CO emission is quite strong. It therefore appears that in the broad ISO beam the [C ii] emission was dominated by the reflection nebula surrounding BD+40°4124, while the high J CO lines originated from the adjacent younger and more deeply embedded binary system V 1318 Cyg.

Context. The hydroxyl radical (OH) is found in various environments within the interstellar medium (ISM) of the Milky Way and external galaxies, mostly either in diffuse interstellar clouds or in the warm, dense environments of newly formed low-mass and high-mass stars, i.e., in the dense shells of compact and ultracompact HII regions (UCHIIRs). Until today, most studies of interstellar OH involved the molecule’s radio wavelength hyperfine structure (hfs) transitions. These lines are generally not in local thermodynamical equilibrium (LTE) and either masing or over-cooling complicates their interpretation. In the past, observations of transitions between different rotational levels of OH, which are at far-infrared (FIR) wavelengths, have suffered from limited spectral and angular resolution. Since these lines have critical densities many orders of magnitude higher than the radio wavelength ground state hfs lines and are emitted from levels with more than 100 K above the ground state, when observed in emission, they probe very dense and warm material. Aims. We aim to probe the warm and dense molecular material surrounding the UCHIIR/OH maser sources W3(OH), G10.62 − 0.39 and NGC 7538 IRS1 by studying the 2Π1/2, J = 3/2 − 1/2 rotational transition of OH in emission and, toward the last source also the molecule’s 2Π3/2, J = 5/2 − 3/2ground-state transition in absorption. Methods. We used the Stratospheric Observatory For Infrared Astronomy (SOFIA) to observe these OH lines, which are near 1.84 THz (163 μm) and 2.51 THz (119.3 μm), with high angular (~16′′/11′′) and spectral resolution (better than 1 km s-1). Results. We clearly detect the OH lines, some of which are blended with each other. Employing non-LTE radiative transfer calculations we predict line intensities using models of a low OH abundance envelope versus a compact, high-abundance source corresponding to the origin of the radio OH lines. From the observed velocities and line-widths we can place constraints on the origin of the emission, and with detailed modeling we show for instance that the OH emission of W3(OH) comes from the UCHIIR and not from the envelope of the nearby hot-core. Conclusions. The FIR lines of the OH molecule provide important information on the density and temperature structure of UCHIIRs. Taking a low-abundance envelope component is not sufficient to reproduce the spectra for W3(OH) and G10.62 − 0.39, a compact, high OH column density source – corresponding to the OH radio emitting sources is definitively required.

We report SOFIA/GREAT, Herschel/HIFI, and ground-based velocity-resolved spectroscopy of carbon monoxide (CO) rotational transitions from J = 2–1 to J = 16–15 toward two positions in the circum-nuclear disk (CND) in our Galactic center. Radiative transfer models were used to derive information on the physical state of the gas traced by CO. The excitation of the CO gas cannot be explained by a single physical component, but is clearly the superposition of various warm gas phases. In a two-component approach, our large velocity gradient (LVG) analysis suggests high temperatures of ~200 K with moderate gas densities of only ~104.5 cm-3 for the bulk of the material. A higher excited phase, carrying ~20–30% of the column densities, is warmer (~300–500 K) but only slightly denser (~105.3 cm-3). These densities are too low to self-stabilize the clumps against their high internal turbulence and fall below the Roche density (>107 cm-3) at 1.5 pc galactocentric distance. We conclude that the bulk of the material in the CND is not organized by self-gravity nor stable against tidal disruption, and must be transient.

We report SOFIA/GREAT, Herschel/HIFI, and ground-based velocity-resolved spectroscopy of carbon monoxide (CO) rotational transitions from J=2-1 to J=16-15 toward two positions in the circum-nuclear disk (CND) in our Galactic center. Radiative transfer models were used to derive information on the physical state of the gas traced by CO. The excitation of the CO gas cannot be explained by a single physical component, but is clearly the superposition of various warm gas phases. In a two-component approach, our large velocity gradient (LVG) analysis suggests high temperatures of ~200 K with moderate gas densities of only ~10^4.5 cm^-3 for the bulk of the material. A higher excited phase, carrying ~20-30% of the column densities, is warmer (~300-500 K) but only slightly denser ~10^5.3 cm^-3. These densities are too low to self-stabilize the clumps against their high internal turbulence and fall below the Roche density (>10^7 cm^-3) at 1.5 pc galactocentric distance. We conclude that the bulk of the material in the CND is not organized by self-gravity nor stable against tidal disruption, and must be transient.