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17 pags., 16 figs., 2 tabs., 3 apps., Hydrogen cyanide (HCN) is considered a good tracer of the dense molecular gas that serves as fuel for star formation. However, recent large-scale surveys of giant molecular clouds (GMCs) have detected extended HCN rotational line emission far from star-forming cores. Such observations often spectroscopically resolve the HCN J = 1-0 (partially also the J = 2-1 and 3-2) hyperfine structure (HFS). A precise determination of the physical conditions of the gas requires treating the HFS line overlap effects. Here, we study the HCN HFS excitation and line emission using nonlocal radiative transfer models that include line overlaps and new HFS-resolved collisional rate coefficients for inelastic collisions of HCN with both para-H2 and ortho-H2 (computed via the scaled-infinite order sudden approximation up to Tk = 500 K). In addition, we account for the role of electron collisions in the HFS level excitation. We find that line overlap and opacity effects frequently produce anomalous HCN J = 1-0 HFS line intensity ratios (i.e., inconsistent with the common assumption of the same Tex for all HFS lines) as well as anomalous HFS line width ratios. Line overlap and electron collisions also enhance the excitation of the higher J rotational lines. Our models explain the anomalous HCN J = 1-0 HFS spectra observed in the Orion Bar and Horsehead photodissociation regions. As shown in previous studies, electron excitation becomes important for molecular gas with H2 densities below a few 105 cm-3 and electron abundances above ∼10-5. We find that when electron collisions are dominant, the relative intensities of the HCN J = 1-0 HFS lines can be anomalous too. In particular, electron excitation can produce low-surface-brightness HCN emission from very extended but low-density gas in GMCs. The existence of such a widespread HCN emission component may affect the interpretation of the extragalactic relationship HCN luminosity versus star-formation rate. Alternatively, extended HCN emission may arise from dense star-forming cores and become resonantly scattered by large envelopes of lower density gas. There are two scenarios-namely, electron-assisted (weakly) collisionally excited versus scattering-that lead to different HCN J = 1-0 HFS intensity ratios, which can be tested on the basis of observations., We thank A. Faure for sharing his HCN-HFS + e rate coefficients in tabulated form. We warmly thank S. Cuadrado, J. Pety, and M. Gerin for providing the HCN J = 1–0 spectra of the Orion Bar and Horsehead, and for useful discussion on the HCN J = 1–0 HFS emission in Orion B. We thank our referee for concise and illuminating comments. J.R.G. and M.G.S.M. thank the Spanish MCINN for funding support under grant PID2019-106110GB-I00.

28 pags., 21 figs., 9 tabs. -- This paper is dedicated to the memory of Bruce Swinyard, for his mentorship and his major contributions to the SPIRE-FTS performance and calibration., Context. Star-forming galaxies emit bright molecular and atomic lines in the submillimeter and far-infrared (FIR) domains. However, it is not always clear which gas heating mechanisms dominate and which feedback processes drive their excitation. Aims. The Sgr B2 complex is an excellent template to spatially resolve the main OB-type star-forming cores from the extended cloud environment and to study the properties of the warm molecular gas in conditions likely prevailing in distant extragalactic nuclei. Methods. We present 168 arcminspectral images of Sgr B2 taken with Herschel/SPIRE-FTS in the complete ∼450-1545 GHz band. We detect ubiquitous emission from mid-J CO (up to J = 12-11), HO 2-2, [C I] 492, 809 GHz, and [N II] 205 μm lines. We also present velocity-resolved maps of the SiO (2-1), NH, HCN, and HCO(1-0) emission obtained with the IRAM 30 m telescope. Results. The cloud environment (∼1000 pcaround the main cores) dominates the emitted FIR (∼80%), HO 752 GHz (∼60%) mid-J CO (∼91%), [C I] (∼93%), and [N II] 205 μm (∼95%) luminosity. The region shows very extended [N II] 205 μm emission (spatially correlated with the 24 and 70 μm dust emission) that traces an extended component of diffuse ionized gas of low ionization parameter (U 10) and low L/M4-11 LMratios (scaling as ≈ T). The observed FIR luminosities imply a flux of nonionizing photons equivalent to G≈ 10. All these diagnostics suggest that the complex is clumpy and this allows UV photons from young massive stars to escape from their natal molecular cores. The extended [C I] emission arises from a pervasive component of neutral gas with n≃ 10cm. The high ionization rates in the region, produced by enhanced cosmic-ray (CR) fluxes, drive the gas heating in this component to T≃ 40-60 K. The mid-J CO emission arises from a similarly extended but more pressurized gas component (P/≃ 10K cm): Spatially unresolved clumps, thin sheets, or filaments of UV-illuminated compressed gas (n≃ 10cm). Specific regions of enhanced SiO emission and high CO-to-FIR intensity ratios (I/I≃ 10) show mid-J CO emission compatible with C-type shock models. A major difference compared to more quiescent star-forming clouds in the disk of our Galaxy is the extended nature of the SiO and NHemission in Sgr B2. This can be explained by the presence of cloud-scale shocks, induced by cloud-cloud collisions and stellar feedback, and the much higher CR ionization rate (>10s) leading to overabundant Hand NH. Conclusions. Sgr B2 hosts a more extreme environment than star-forming regions in the disk of the Galaxy. As a usual template for extragalactic comparisons, Sgr B2 shows more similarities to nearby ultra luminous infrared galaxies such as Arp 220, including a "deficit" in the [C I]/FIR and [N II]/FIR intensity ratios, than to pure starburst galaxies such as M 82. However, it is the extended cloud environment, rather than the cores, that serves as a useful template when telescopes do not resolve such extended regions in galaxies., We thank the Spanish MICIU for funding support under grants AYA2017-85111-P and PID2019-106110GB-I00.

18 pags., 21 figs., 5 tabs, 1 app., Strong winds and ultraviolet (UV) radiation from O-type stars disrupt and ionize their molecular core birthplaces, sweeping up material into parsec-size shells. Owing to dissociation by starlight, the thinnest shells are expected to host low molecular abundances and therefore little star formation. Here, we expand previous maps made with observations using the IRAM 30 m telescope (at 11″ ≃ 4500 AU resolution) and present square-degree 12CO and 13CO (J = 2-1) maps of the wind-driven "Veil bubble"that surrounds the Trapezium cluster and its natal Orion molecular core (OMC). Although widespread and extended CO emission is largely absent from the Veil, we show that several CO "globules"exist that are blueshifted in velocity with respect to OMC and are embedded in the [C » II] 158 μm-bright shell that confines the bubble. This includes the first detection of quiescent CO at negative local standard of rest velocities in Orion. Given the harsh UV irradiation conditions in this translucent material, the detection of CO globules is surprising. These globules are small (Rg = 7100 AU), not massive (Mg = 0.3 M⊙ ), and are moderately dense: nH = 4 × 104 cm-3 (median values). They are confined by the external pressure of the shell, Pext∕ k ≳ 107 cm-3 K, and are likely magnetically supported. They are either transient objects formed by instabilities or have detached from pre-existing molecular structures, sculpted by the passing shock associated with the expanding shell and by UV radiation from the Trapezium. Some represent the first stages in the formation of small pillars, others of isolated small globules. Although their masses (Mg, We warmly thank the operators, AoDs, and chefs at the IRAM 30 m telescope for their support while the CO observations were conducted. This work is also based on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NNA17BF53C, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. We acknowledge the work, during the C+ upGREAT square degree survey of Orion, of the USRA and NASA staff of the Armstrong Flight Research Center in Palmdale, the Ames Research Center in Mountain View (California), and the Deutsches SOFIA Institut. We thank the Spanish MICIU for funding support under grant AYA2017-85111-P. Research on the ISM at Leiden Observatory is supported through a Spinoza award.

The properties of molecular gas, the fuel that forms stars, inside the cavity of the circumnuclear disk (CND) are not well constrained. We present results of a velocity-resolved submillimeter scan (~480 to 1250 GHz) and [C ii] 158 μm line observations carried out with Herschel/HIFI toward Sgr A*; these results are complemented by a ~2′×2′ (12)CO (J=3-2) map taken with the IRAM 30 m telescope at ~7″ resolution. We report the presence of high positive-velocity emission (up to about +300 km s(−1)) detected in the wings of (12)CO J=5-4 to 10-9 lines. This wing component is also seen in H(2)O (1(1,0)-1(0,1)), a tracer of hot molecular gas; in [C ii]158 μm, an unambiguous tracer of UV radiation; but not in [C i] 492, 806 GHz. This first measurement of the high-velocity (12)CO rotational ladder toward Sgr A* adds more evidence that hot molecular gas exists inside the cavity of the CND, relatively close to the supermassive black hole (< 1 pc). Observed by ALMA, this velocity range appears as a collection of (12)CO (J=3-2) cloudlets lying in a very harsh environment that is pervaded by intense UV radiation fields, shocks, and affected by strong gravitational shears. We constrain the physical conditions of the high positive-velocity CO gas component by comparing with non-LTE excitation and radiative transfer models. We infer T(k)≃400 K to 2000 K for n(H)≃(0.2-1.0)·10(5) cm(−3). These results point toward the important role of stellar UV radiation, but we show that radiative heating alone cannot explain the excitation of this ~10-60 M(⊙) component of hot molecular gas inside the central cavity. Instead, strongly irradiated shocks are promising candidates.

22 pags.; 17 figs., 3 tabs., 3 apps., Young massive stars regulate the physical conditions, ionization, and fate of their natal molecular cloud and surroundings. It is important to find tracers that quantify the stellar feedback processes that take place on different spatial scales. We present -85 arcmin velocity-resolved maps of several submillimeter molecular lines, taken with Herschel/HIFI, toward the closest high-mass star-forming region, the Orion molecular cloud 1 core (OMC-1). The observed rotational lines include probes of warm and dense molecular gas that are difficult, if not impossible, to detect from ground-based telescopes: CH (J = 1-0), CO (J = 10-9), HCO (J = 6-5), HCN (J = 6-5), and CH (N, J = 1, 3/2-1, 1/2). These lines trace an extended but thin layer (AV ≃ 3-6 mag or ~10 cm) of molecular gas at high thermal pressure, P = nH · Tk ≈ 107-109 cm K, associated with the far-ultraviolet (FUV) irradiated surface of OMC-1. The intense FUV radiation field - emerging from massive stars in the Trapezium cluster - heats, compresses, and photoevaporates the cloud edge. It also triggers the formation of specific reactive molecules such as CH+. We find that the CH (J = 1-0) emission spatially correlates with the flux of FUV photons impinging the cloud: G0 from ~10 to ~10. This relationship is supported by constant-pressure photodissociation region (PDR) models in the parameter space P=G ≈ [5 × 10 - 8 × 10] cm K where many observed PDRs seem to lie. The CH+ (J = 1-0) emission also correlates with the extended infrared emission from vibrationally excited H (v ≫ 1), and with that of [C II] 158 μm and CO J = 10-9, all emerging from FUV-irradiated gas. These spatial correlations link the presence of CH+ to the availability of C+ ions and of FUV-pumped H2 (v ≫ 1) molecules.We conclude that the parsec-scale CH emission and narrow-line (δ ≃ 3 km s) mid-J CO emission arises from extended PDR gas and not from fast shocks. PDR line tracers are the smoking g of the stellar feedback from young massive stars. The PDR cloud surface component in OMC-1, with a mass density of 120-240 M⊙pc, represents ~5-10% of the total gas mass; however, it dominates the emitted line luminosity, the average CO J = 10-9 surface luminosity in the mapped region being ~35 times brighter than that of CO J = 2-1. These results provide insights into the source of submillimeter CH+ and mid-J CO emission from distant star-forming galaxies., We thank the Spanish MICIU for funding support under grants AYA2016-75066-C2-1-P and AYA2017-85111-P, and the ERC for support under grant ERC-2013-Syg-610256-NANOCOSMOS.

We present 1"-resolution ALMA observations of the circumnuclear disk (CND) and the environment around SgrA*. The images unveil the presence of small spatial scale CO (J=3-2) molecular "cloudlets" within the central pc of the Milky Way, moving at high speeds, up to 300 km/s along the line-of-sight. The CO-emitting structures show intricate morphologies: extended and filamentary at high negative-velocities (v_LSR < -150 km/s), more localized and clumpy at extreme positive-velocities (v_LSR > +200 km/s). Based on the pencil-beam CO absorption spectrum toward SgrA* synchrotron emission, we also present evidence for a diffuse gas component producing absorption features at more extreme negative-velocities (v_LSR < -200 km/s). The CND shows a clumpy spatial distribution. Its motion requires a bundle of non-uniformly rotating streams of slightly different inclinations. The inferred gas density peaks are lower than the local Roche limit. This supports that CND molecular cores are transient. We apply the two standard orbit models, spirals vs. ellipses, invoked to explain the kinematics of the ionized gas streamers around SgrA*. The location and velocities of the CO cloudlets are inconsistent with the spiral model, and only two of them are consistent with the Keplerian ellipse model. Most cloudlets, however, show similar velocities that are incompatible with the motions of the ionized streamers or with gas bounded to the central gravity. We speculate that they are leftovers of more massive, tidally disrupted, clouds that fall into the cavity, or that they originate from instabilities in the inner rim of the CND and infall from there. Molecular cloudlets, all together with a mass of several 10 M_Sun, exist around SgrA*. Most of them must be short-lived: photoevaporated by the intense stellar radiation field, blown away by winds from massive stars, or disrupted by strong gravitational shears., Accepted for publication in A&A. 21 pages, 19 figures (includes corrections by language editor)

The properties of molecular gas, the fuel that forms stars, inside the cavity of the circumnuclear disk (CND) are not well constrained. We present results of a velocity-resolved submillimeter scan (~480 to 1250 GHz}) and [CII]158um line observations carried out with Herschel/HIFI toward Sgr A*; these results are complemented by a ~2'x2' CO (J=3-2) map taken with the IRAM 30 m telescope at ~7'' resolution. We report the presence of high positive-velocity emission (up to about +300 km/s) detected in the wings of CO J=5-4 to 10-9 lines. This wing component is also seen in H2O (1_{1,0}-1_{0,1}) a tracer of hot molecular gas; in [CII]158um, an unambiguous tracer of UV radiation; but not in [CI]492,806 GHz. This first measurement of the high-velocity CO rotational ladder toward Sgr A* adds more evidence that hot molecular gas exists inside the cavity of the CND, relatively close to the supermassive black hole (< 1 pc). Observed by ALMA, this velocity range appears as a collection of CO (J=3-2) cloudlets lying in a very harsh environment that is pervaded by intense UV radiation fields, shocks, and affected by strong gravitational shears. We constrain the physical conditions of the high positive-velocity CO gas component by comparing with non-LTE excitation and radiative transfer models. We infer T_k~400 K to 2000 K for n_H~(0.2-1.0)x10^5 cm^-3. These results point toward the important role of stellar UV radiation, but we show that radiative heating alone cannot explain the excitation of this ~10-60 M_Sun component of hot molecular gas inside the central cavity. Instead, strongly irradiated shocks are promising candidates., Accepted for publication in A&A Letters ( this v2 includes corrections by language editor)