arXiv subjects

R. Higgins

Publications and source records attributed to R. Higgins.

At least 19 recordsLinked to original sources

arXiv2026

Observations of ionized carbon towards the $\gamma$-ray-bright supernova remnant RX J1713.7-3946

The origin of Galactic Cosmic Rays (CRs), particularly at sub-GeV energies, remains uncertain due to their difficulty in being traced. One possible tracer of low-energy CRs is ionised carbon ([C II]), which may be enhanced in regions affected by CR-induced ionisation. We present observations of [C II] 158 $\mu$m line emission across the $\gamma$-ray-bright supernova remnant (SNR) RX J1713.7-3946 obtained with SOFIA. These data are compared with molecular and atomic gas from Mopra ($^{12}$CO), Nanten ($^{12}$CO) and SGPS (HI), and high-energy emission from TeV $\gamma$-ray H.E.S.S. and X-ray XMM-Newton. We find [C II] emission follows the atomic gas more closely than molecular gas, particularly in regions near the SNR shock front. Ratios of [C II] intensity to gas column density vary across the remnant, with peak values coinciding with regions of enhanced TeV $\gamma$-ray emission. To put the [C II] in a wider context, we examined pointings from the Herschel GOT C+ survey. Our analysis of the GOT C+ data shows no significant difference in the I[C II]/I[$^{12}$CO] ratio for observations towards star formation regions, HII regions and SNRs. To assess the origin of carbon ionisation, we model [C II] emissivity using the photoionisation code CLOUDY. We find UV photons and CRs can produce comparable levels of [C II] emission, assuming low-energy CRs (< 1 GeV) are accelerated and trapped within the SNR shock. These results highlight the potential of [C II] as a tracer of CR ionisation and the importance of combining multi-wavelength observations to probe CR interactions in SNRs.

astro-ph.HE↗

arXiv2026

Velocity-resolved [O I] 63,145 um, [C II] 158 um, and OH mapping along the Orion BN/KL explosive outflow and irradiated shocks

Stellar mergers produce explosive outflows that serve as transient sources of IR line luminosity and inject mechanical energy early into the natal molecular cloud. We present the first velocity-resolved maps of the [O I] 63 and 145 um fine-structure line emission from the wide-angle outflow in Orion BN/KL, the nearest explosive outflow. The data were obtained with SOFIA and include sensitive [C II] 158 um and OH maps. They allowed us to disentangle the quiescent cloud gas from the outflow, traced by a broader [O I] component with a line FWHM of about 20-30 km/s and exhibiting a spatial distribution similar to that of the shock-excited H2 emission seen with JWST. The OH 119 um line shows a prominent P-Cygni profile covering 160 km/s, similar to the very broad CO lines. The total [O I] 63 and 145 line luminosity is remarkably high, 86.5 L_sun, comparable to the H2 and CO line luminosities, implying an outflow mass-loss rate of (9.1+/-2.6)x10^-3 M_sun/yr and a mass of 3.3-5.9 M_sun. The [O I] 63 / 145 and [O I] 63 / [C II] 158 intensity ratios reach very high values in the line wings (20-30 and 40-60, respectively), exceeding those found in PDRs. These ratios are consistent with the presence of dense (10^5 to 10^6 cm^-3 ) and warm (~500 K) postshock gas. We analyzed the fine-structure line-wing intensities using magnetized shock models that include UV irradiation, to which the [C II] 158 line intensity is particularly sensitive. We find that the [O I] and [C II] intensities are consistent with emission from dissociative J-type shocks with velocities of 30-40 km/s and preshock gas densities of a few 10^4 cm^-3, illuminated by external UV radiation generated by surrounding fast shocks and possibly by massive (proto)stars in the region. We also report a broad [O I] emission feature around the BN star, which we attribute to an unresolved outflow or wind bow shock.

astro-ph.GA↗

arXiv2026

Space as a spectroscopic laboratory: High-resolution spectroscopy of the [$^{13}$C II] hyperfine structure with SOFIA/upGREAT

The [$^{12}$C II] emission at 158 $\mu$m is a key cooling line of the interstellar medium and traces gas kinematics in spectrally resolved observations. Its spectral profile is often modified by optical depth effects. The intrinsic line shape can be reconstructed by comparison with emission from the less abundant $^{13}$C isotope. Due to the additional neutron spin, [$^{13}$C II] emission splits into three hyperfine structure (hfs) transitions. Laboratory measurements have provided the centroid frequency and the strongest component ($F=2-1$); the two weaker components ($F=1-0$ and $F=1-1$) have been inferred only from quantum-mechanical calculations. The magnetic-dipole hfs constants, from which the transition frequencies follow, have not been measured experimentally. The high spectral resolution of observations with the upgraded German Receiver for Astronomy at Terahertz Frequencies (upGREAT) on board SOFIA enabled simultaneous detection of all three hfs transitions. From these astronomical data we determine, for the first time, the magnetic-dipole hfs constants $A_{1/2}^{\rm hf} = 810.71(11)$ MHz and $A_{3/2}^{\rm hf} = 162.18(5)$ MHz of the [$^{13}$C II] $2s^2\,2p\,{}^2P^\circ$ ground term. Combined with the laboratory centroid frequency, this yields the rest frequencies of all three hfs lines. Using [$^{12}$C II] as a reference, we also improve the precision of the [$^{13}$C II] centroid frequency. This work shows that spectrally resolved astronomical observations can constrain fundamental atomic properties, with hfs precision rivaling laboratory measurements. The approach extends to other atomic and molecular transitions where laboratory data are difficult to obtain.

astro-ph.GA↗

arXiv2025

Globules and pillars in Cygnus X IV. Velocity-resolved [OI] 63 mu map of a peculiar proplyd-like object

We investigated an isolated, globule-shaped object (0.37x0.11 pc), located near the centre of the Cygnus OB2 cluster and named proplyd #7 in optical observations. The source can be a massive star (with or without disc) with a HII region or a G-type T Tauri star with a photo-evaporating disc, embedded in a molecular envelope. We obtained a map of the OI line at 63 micron with 6" angular resolution and employed archival data of the CII 158 micron line (14" resolution), using the upGREAT heterodyne receiver aboard SOFIA. We also collected IRAM 30m CO data at 1mm (11" resolution). All the lines were detected across the whole object. The peak integrated OI emission of ~5 K km/s is located ~10" west of an embedded YSO. The OI and CII data near the source show bulk emission at ~11 km/s and a line wing at ~13 km/s, while the 12CO 2-1 data reveal additional blue-shifted high-velocity emission. The KOSMA-tau PDR model can explain the emissions in the tail with a low external UV field (<350 Go, mostly consistent with our UV field estimates), but not at the location of the YSO. There, the high line intensities and increased line widths for all lines and a possible bipolar CO outflow suggest the presence of a protostellar disc. However, the existence of a thermal HII region, revealed by combining existing and new radio continuum data, points towards a massive star - and not a T Tauri-type one. We derived molecular and atomic gas masses of ~20 Msun and a few Msun, respectively. The photo-evaporation (only considering external illumination) lifetime of 1.6x10^5 yrs is shorter than the free-fall lifetime of 5.2x10^5 yrs; thus, we find that proplyd #7 might not have had the time to produce many more stars.

astro-ph.GA↗

arXiv2024

GMF G214.5-1.8 as traced by CO: I -- cloud-scale CO freeze-out as a result of a low cosmic-ray ionisation rate

We present an analysis of the outer Galaxy giant molecular filament (GMF) G214.5-1.8 (G214.5) using IRAM 30m data of $^{12}$CO, $^{13}$CO and C$^{18}$O. We find that the $^{12}$CO (1-0) and (2-1) derived excitation temperatures are near identical and are very low, with a median of 8.2 K, showing that the gas is extremely cold across the whole cloud. Investigating the abundance of $^{13}$CO across G214.5, we find that there is a significantly lower abundance along the entire 13 pc spine of the filament, extending out to a radius of $\sim 0.8$ pc, corresponding to $A_v \gtrsim 2$ mag and $T_{dust} \lesssim 13.5$ K. Due to this, we attribute the decrease in abundance to CO freeze-out, making G214.5 the largest scale example of freeze-out yet. We construct an axisymmetric model of G214.5's $^{13}$CO volume density considering freeze-out and find that to reproduce the observed profile significant depletion is required beginning at low volume densities, $n\gtrsim2000$ cm$^{-3}$. Freeze-out at this low number density is possible only if the cosmic-ray ionisation rate is $\sim 1.9 \times 10^{-18}$ s$^{-1}$, an order of magnitude below the typical value. Using timescale arguments, we posit that such a low ionisation rate may lead to ambipolar diffusion being an important physical process along G214.5's entire spine. We suggest that if low cosmic-ray ionisation rates are more common in the outer Galaxy, and other quiescent regions, cloud-scale CO freeze-out occurring at low column and number densities may also be more prevalent, having consequences for CO observations and their interpretation.

astro-ph.GA↗

arXiv2023

Identifying physical structures in our Galaxy with Gaussian Mixture Models: An unsupervised machine learning technique

We explore the potential of the Gaussian Mixture Model (GMM), an unsupervised machine learning method, to identify coherent physical structures in the ISM. The implementation we present can be used on any kind of spatially and spectrally resolved data set. We provide a step-by-step guide to use these models on different sources and data sets. Following the guide, we run the models on NGC 1977, RCW 120 and RCW 49 using the [CII] 158 $\mu$m mapping observations from the SOFIA telescope. We find that the models identified 6, 4 and 5 velocity coherent physical structures in NGC 1977, RCW 120 and RCW 49, respectively, which are validated by analysing the observed spectra towards these structures and by comparison to earlier findings. In this work we demonstrate that GMM is a powerful tool that can better automate the process of spatial and spectral analysis to interpret mapping observations.

astro-ph.GA↗

arXiv2022

The SOFIA FEEDBACK Legacy Survey: Dynamics and mass ejection in the bipolar HII region RCW 36

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).

astro-ph.GA↗

arXiv2022

HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules -- I. Survey description and a first look toward W3(OH), W3 IRS5 and NGC 7538 IRS1

The HyGAL SOFIA legacy program surveys six hydride molecules -- ArH+, OH+, H2O+, SH, OH, and CH -- and two atomic constituents -- C+ and O -- within the diffuse interstellar medium (ISM) by means of absorption-line spectroscopy toward 25 bright Galactic background continuum sources. This detailed spectroscopic study is designed to exploit the unique value of specific hydrides as tracers and probes of different phases of the ISM, as demonstrated by recent studies with the Herschel Space Observatory. The observations performed under the HyGAL program will allow us to address several questions related to the lifecycle of molecular material in the ISM and the physical processes that impact its phase transition, such as: (1) What is the distribution function of the H2 fraction in the ISM? (2) How does the ionization rate due to low-energy cosmic-rays vary within the Galaxy? (3) What is the nature of interstellar turbulence, and what mechanisms lead to its dissipation? This overview discusses the observing strategy, synergies with ancillary and archival observations, the data reduction and analysis schemes adopted; and presents the first results obtained toward three of the survey targets, W3(OH), W3IRS5 and NGC7538IRS1. Robust measurements of the column densities of these hydrides -- obtained through widespread observations of absorption lines-- help address the questions raised, and there is a timely synergy between these observations and the development of theoretical models, particularly pertaining to the formation of H2 within the turbulent ISM. The provision of enhanced HyGAL data products will therefore serve as a legacy for future ISM studies.

astro-ph.GA↗

arXiv2021

Self-absorption in [CII], $^{12}$CO, and HI in RCW120. Building up a geometrical and physical model of the region

Revealing the 3D dynamics of HII regions and their associated molecular clouds is important for understanding the longstanding problem as to how stellar feedback affects the density structure and kinematics of the interstellar medium. We employed observations of the HII region RCW 120 in [CII], observed within the SOFIA legacy program FEEDBACK, and the $^{12}$CO and $^{13}$CO (3$\to$2) lines, obtained with APEX. In addition we used HI data from the Southern Galactic Plane Survey. Two radiative transfer models were used to fit the observed data. A line profile analysis with the 1D non-LTE radiative transfer code SimLine proves that the CO emission cannot stem from a spherically symmetric molecular cloud configuration. With a two-layer multicomponent model, we then quantified the amount of warm background and cold foreground gas. There is a deficit of CO emission along the line-of-sight toward the center of the HII region which indicates that the HII region is associated with a flattened molecular cloud. Self-absorption in the CO line may hide signatures of infalling and expanding molecular gas. The [CII] emission arises from an expanding [CII] bubble and from the PDRs. A significant part of [CII] emission is absorbed in a cool (~60-100 K), low-density (<500 cm$^{-3}$) atomic foreground layer with a thickness of a few parsec. We propose that the RCW 120 HII region formed in a flattened molecular cloud and is now bursting out of its parental cloud. The compressed surrounding molecular layer formed a torus around the spherically expanding HII bubble. This scenario can possibly be generalized for other HII bubbles and would explain the observed "flat" structure of molecular clouds associated with HII bubbles. We suggest that the [CII] absorption observed in many star-forming regions is at least partly caused by low-density, cool, HI-envelopes surrounding the molecular clouds.

astro-ph.GA↗

arXiv2021

SOFIA-upGREAT imaging spectroscopy of the [C II] 158um fine structure line of the Sgr B region in the Galactic center

We report SOFIA-upGREAT spectroscopic imaging of the [C II] 158um spectral line, as well as a number of [O I] 63um spectra, across a 67x45 pc field toward the Sgr B region in our Galactic center. The fully-sampled and velocity-resolved [C II] images have 0.55 pc spatial and 1 km/s velocity resolutions. We find that Sgr B extends as a coherent structure spanning some 34 pc along the Galactic plane. Bright [C II] emission encompasses Sgr B1 (G0.5-0.0), the G0.6-0.0 HII region, and passes behind and beyond the luminous star forming cores toward Sgr B2 (G0.7-0.0). Sgr B is a major contributor to the entire Galactic center's [C II] luminosity, with surface brightness comparable to [C II] from the Arches region. [C II], 70um, and 20cm emission share nearly identical spatial distributions. Combined with the lack of [C II] self-absorption, this indicates that these probes trace UV on the near surfaces of more extended clouds visible in CO isotopologues and 160um continuum. Stars from regions of local star formation likely dominate the UV field. Photodissociation regions and HII regions contribute similar amounts of [C II] flux. The extreme star formation cores of Sgr B2 contribute negligible amounts to the total [C II] intensity from the Sgr B region. Velocity fields and association with a narrow dust lane indicate that they may have been produced in a local cloud-cloud collision. The cores are likely local analogs of the intense star formation regions where ideas to explain the "C+ deficit" in ultra-luminous galaxies can be tested.

astro-ph.GA↗

arXiv2021

CCAT-prime Collaboration: Science Goals and Forecasts with Prime-Cam on the Fred Young Submillimeter Telescope

We present a detailed overview of the science goals and predictions for the Prime-Cam direct detection camera/spectrometer being constructed by the CCAT-prime collaboration for dedicated use on the Fred Young Submillimeter Telescope (FYST). The FYST is a wide-field, 6-m aperture submillimeter telescope being built (first light in mid-2024) by an international consortium of institutions led by Cornell University and sited at more than 5600 meters on Cerro Chajnantor in northern Chile. Prime-Cam is one of two instruments planned for FYST and will provide unprecedented spectroscopic and broadband measurement capabilities to address important astrophysical questions ranging from Big Bang cosmology through reionization and the formation of the first galaxies to star formation within our own Milky Way galaxy. Prime-Cam on the FYST will have a mapping speed that is over ten times greater than existing and near-term facilities for high-redshift science and broadband polarimetric imaging at frequencies above 300 GHz. We describe details of the science program enabled by this system and our preliminary survey strategies.

astro-ph.CO↗

arXiv2021

Observation and calibration strategies for large-scale multi-beam velocity-resolved mapping of the [CII] emission in the Orion molecular cloud

Context. The [CII] 158micron far-infrared fine-structure line is one of the dominant cooling lines of the star-forming interstellar medium (ISM). Hence [CII] emission originates in and thus can be used to trace a range of ISM processes. Velocity-resolved large-scale mapping of [CII] in star-forming regions provides a unique perspective of the kinematics of these regions and their interactions with the exciting source of radiation. Aims. We explore the scientific applications of large-scale mapping of velocity-resolved [CII] observations. With the [CII] observations, we investigate the effect of stellar feedback on the ISM. We present the details of observation, calibration, and data reduction using a heterodyne array receiver mounted on an airborne observatory. Results. A square-degree [CII] map with a spectral resolution of 0.3 km/s is presented. The scientific potential of this data is summarized with discussion of mechanical and radiative stellar feedback, filament tracing using [CII], [CII] opacity effects, [CII] and carbon recombination lines, and [CII] interaction with the large molecular cloud. The data quality and calibration is discussed in detail, and new techniques are presented to mitigate the effects of unavoidable instrument deficiencies (e.g. baseline stability) and thus to improve the data quality. A comparison with a smaller [CII] map taken with the Herschel/Heterodyne Instrument for the Far-Infrared (HIFI) spectrometer is presented.

astro-ph.IM↗

arXiv2020

Molecular globules in the Veil bubble of Orion. IRAM 30m 12CO, 13CO, and C18O 2-1 expanded maps of Orion A

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 taken with the IRAM 30m telescope 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 and are embedded in the [CII]158um-bright shell that confines the bubble. This includes the first detection of quiescent CO at negative LSR velocities in Orion. Given the harsh UV irradiation conditions in this translucent material, the detection of CO globules is surprising. These globules are small (R=7,100 AU), not massive (M=0.3M_Sun), and are moderately dense: n_ H=4x10^4 cm^-3 (median values). They are confined by the external pressure of the shell, P_ext/k~10^7 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 do not suggest they will form stars, one globule matches the position of a known YSO. The lack of extended CO in the "Veil shell'' demonstrates that feedback from massive stars expels, agitates, and reprocesses most of the disrupted molecular cloud gas, thereby limiting the star-formation rate in the region. The presence of globules is a result of this feedback.

astro-ph.GA↗

arXiv2020

[CII] 158 {\mu}m self-absorption and optical depth effects

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

astro-ph.GA↗

arXiv2019

Disruption of the Orion Molecular Core 1 by the stellar wind of the massive star ${\theta}^1$ Ori C

Massive stars inject mechanical and radiative energy into the surrounding environment, which stirs it up, heats the gas, produces cloud and intercloud phases in the interstellar medium, and disrupts molecular clouds (the birth sites of new stars). Stellar winds, supernova explosions and ionization by ultraviolet photons control the lifetimes of molecular clouds. Theoretical studies predict that momentum injection by radiation should dominate that by stellar winds, but this has been difficult to assess observationally. Velocity-resolved large-scale images in the fine-structure line of ionized carbon ([C II]) provide an observational diagnostic for the radiative energy input and the dynamics of the interstellar medium around massive stars. Here we report observations of a one-square-degree region (about 7 parsecs in diameter) of Orion molecular core -- the region nearest to Earth that exhibits massive-star formation -- at a resolution of 16 arcseconds (0.03 parsecs) in the [C II] line at 1.9 terahertz (158 micrometres). The results reveal that the stellar wind originating from the massive star ${\theta}^{1}$ Orionis C has swept up the surrounding material to create a bubble roughly four parsecs in diameter with a 2,600-solar-mass shell, which is expanding at 13 kilometres per second. This finding demonstrates that the mechanical energy from the stellar wind is converted very efficiently into kinetic energy of the shell and causes more disruption of the Orion molecular core 1 than do photo-ionization and evaporation or future supernova explosions.

astro-ph.GA↗

arXiv2016

Warm ISM in the Sgr A Complex. I: Mid-J CO, atomic carbon, ionized atomic carbon,and ionized nitrogen sub-mm/FIR line observations with the Herschel-HIFI and NANTEN2/SMART telescopes

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.

astro-ph.GA↗

arXiv2014

Widespread Rotationally-Hot Hydronium Ion in the Galactic Interstellar Medium

We present new observations of the (6,6) and (9,9) inversion transitions of the hydronium ion toward Sagittarius B2(N) and W31C. Sensitive observations toward Sagittarius B2(N) show that the high, ~ 500 K, rotational temperatures characterizing the population of the highly-excited metastable H3O+ rotational levels are present over a wide range of velocities corresponding to the Sagittarius B2 envelope, as well as the foreground gas clouds between the Sun and the source. Observations of the same lines toward W31C, a line of sight that does not intersect the Central Molecular Zone, but instead traces quiescent gas in the Galactic disk, also imply a high rotational temperature of ~ 380 K, well in excess of the kinetic temperature of the diffuse Galactic interstellar medium. While it is plausible that some fraction of the molecular gas may be heated to such high temperatures in the active environment of the Galactic center, characterized by high X-ray and cosmic ray fluxes, shocks and high degree of turbulence, this is unlikely in the largely quiescent environment of the Galactic disk clouds. We suggest instead that the highly-excited states of the hydronium ion are populated mainly by exoergic chemical formation processes and temperature describing the rotational level population does not represent the physical temperature of the medium. The same arguments may be applicable to other symmetric top rotors, such as ammonia. This offers a simple explanation to the long-standing puzzle of the presence of a pervasive, hot molecular gas component in the central region of the Milky Way. Moreover, our observations suggest that this is a universal process, not limited to the active environments associated with galactic nuclei.

astro-ph.GA↗

arXiv2013

The Herschel/HIFI spectral survey of OMC-2 FIR 4 (CHESS): An overview of the 480 to 1902 GHz range

Broadband spectral surveys of protostars offer a rich view of the physical, chemical and dynamical structure and evolution of star-forming regions. The Herschel Space Observatory opened up the terahertz regime to such surveys, giving access to the fundamental transitions of many hydrides and to the high-energy transitions of many other species. A comparative analysis of the chemical inventories and physical processes and properties of protostars of various masses and evolutionary states is the goal of the Herschel CHEmical Surveys of Star forming regions (CHESS) key program. This paper focusses on the intermediate-mass protostar, OMC-2 FIR 4. We obtained a spectrum of OMC-2 FIR 4 in the 480 to 1902 GHz range with the HIFI spectrometer onboard Herschel and carried out the reduction, line identification, and a broad analysis of the line profile components, excitation, and cooling. We detect 719 spectral lines from 40 species and isotopologs. The line flux is dominated by CO, H2O, and CH3OH. The line profiles are complex and vary with species and upper level energy, but clearly contain signatures from quiescent gas, a broad component likely due to an outflow, and a foreground cloud. We find abundant evidence for warm, dense gas, as well as for an outflow in the field of view. Line flux represents 2% of the 7 L_Sol luminosity detected with HIFI in the 480 to 1250 GHz range. Of the total line flux, 60% is from CO, 13% from H2O and 9% from CH3OH. A comparison with similar HIFI spectra of other sources is set to provide much new insight into star formation regions, a case in point being a difference of two orders of magnitude in the relative contribution of sulphur oxides to the line cooling of Orion KL and OMC-2 FIR 4.

astro-ph.GA↗