arXiv subjects

Antoine Gusdorf

Publications and source records attributed to Antoine Gusdorf.

At least 19 recordsLinked to original sources

arXiv2026

Supernova Kinetic Yield oN galactic Emission Tracers (SKYNET) I. Contribution of radiative supernova remnants to Galactic N + emission

Context. The radiative stage of a supernova remnant (SNR) constitutes approximately 90% of its lifetime. Yet, only a few tens of radiative supernova remnants (r-SNRs) have been observed in the Milky Way, while catalogs of young SNRs in their adiabatic stage contain $\sim$ 300 -400 confirmed sources. This deficit reflects the absence of unambiguous tracers for the radiative phase, and stands as a major obstacle to understanding the impact of SNRs on the energetic balance and the chemical state of the interstellar medium. Aims. We aim to identify spectral tracers of r-SNRs to enable their individual or statistical detection across the Galactic plane, and, more generally, to quantify the collective contribution of the Galactic r-SNR population to interstellar line emission. Methods. We present SKYNET, a new predictive framework that couples a physically motivated model of individual r-SNRs, built upon a dedicated version of the Paris-Durham shock code, with a Galactic model that describes the spatial distribution of r-SNRs and the properties of the medium into which they expand. Together, these components allow SKYNET to predict the cumulative emission of Galactic r-SNRs in nearly one million spectral lines. As a first application, we compare the predictions of SKYNET with an Herschel survey of the two fine-structure lines of singly ionized nitrogen. Results. The Galactic distribution predicted by SKYNET shows that random lines of sight toward the Galactic plane inevitably intercept multiple r-SNRs, whose cumulative emission may be associated with specific spectral tracers. SKYNET successfully reproduces the longitudinal profile of N + emission along the Galactic plane, which results from the projection on the sky of the spiral arms structure. The predicted line-ratio distribution matches the mean, the dispersion, and the tail of the observed distribution, showing that the model naturally explains the unexpectedly narrow range of physical conditions of the medium responsible for the N + emission. Comparison with the observed column densities reveals that SKYNET accounts for $\sim$ 20-25% of the total Galactic N + content, demonstrating that radiative SNRs constitute a significant, and previously underappreciated, source of ionization in the Milky Way. The difference between the observed and predicted column densities could be due to the clustering of supernova remnants into superbubbles, which is currently not taken into account by the model, and to the contribution of non-SNR sources such as H II regions. Conclusions. SKYNET offers a new framework for quantifying the cumulative emission of r-SNRs at Galactic scales that can be directly compared with observational surveys of atomic and molecular lines. The first application reveals that SNRs contribute significantly to the ionization of the ISM, highlighting a role that has largely been overlooked.

astro-ph.GA↗

arXiv2026

Low-Frequency Recombination Lines from Galaxies and AGN over Cosmic Time

Radio recombination lines (RRLs) at low frequencies (<10 GHz) can provide a multi-phase view of interstellar gas in nearby galaxies, absorption-line-systems, and AGN. Hydrogen RRLs arise in fully ionized gas and carbon RRLs trace elusive cold-HI and CO-dark molecular gas. Low frequency RRLs are typically stimulated by the radio continuum and thus may be observable within or against radio bright sources out to cosmological distances (z ~ 6). Although long sought after, RRLs were only recently detected outside of the local universe (z ~ 1; Emig et al., 2020, 2023). Such detections have been made possible by the advancement of wide-bandwidth spectral-line surveys on next-generation low-frequency telescopes. Precursors and pathfinders to the SKA have opened up this field of research and will make significant advancements over the next years by enabling surveys over large source samples. The SKA will provide access to the crucial frequency ranges where RRL line intensity is brightest. Furthermore, multi-band SKA measurements will fully characterize gas physical conditions. Key extragalactic science of low frequency RRLs will focus on (i) the conversion of baryonic material into stars across cosmic time, (ii) the evolution of the ISM and its physical conditions in galaxies, and (iii) how gas drives and inhibits AGN activity.

astro-ph.GA↗

arXiv2025

Mass Assembly and Chemical Complexity in the Milky Way

(Sub-)millimeter spectral lines can be used not only to understand the chemical complexity and enrichment history of an observed portion of our Galaxy, but with spectrally resolved lines, they reveal the physical conditions, dynamics, and even the ionisation state and magnetic field strengths of the gas component of our Galaxy. They are prime tracers of mass assembly and structure formation across scales.

astro-ph.GA↗

arXiv2025

Observations of Carbon Radio Recombination Lines with the NenuFAR telescope. I. Cassiopeia A and Cygnus A

Carbon Radio Recombination Lines (CRRLs) at decametre wavelengths trace the diffuse phase of the interstellar medium (ISM) of the Galaxy. Their observation allows to measure physical parameters of this phase. We observed CRRLs with the recently commissioned New Extension in Nançay Upgrading LOFAR (NenuFAR) telescope towards two of the brightest sources at low-frequency (10-85 MHz): Cassiopeia A and Cygnus A (hereafter Cas A and Cyg A respectively), to measure the density n_e and temperature T_e of electrons in line-of-sight clouds. We used NenuFAR's beamforming mode, and we integrated several tens of hours on each source. The nominal spectral resolution was 95.4 Hz. We developed a pipeline to remove radio frequency interference (RFI) contamination and correct the baselines. We then fitted the spectral lines observed in absorption, associated to line-of-sight clouds. Cas A is the brightest source in the sky at low frequencies and represents an appropriate test bench for this new telescope. On this source, we detected 398 Cαlines between principal quantum numbers n=426 and n=826. Cαlines towards Cyg A were fainter. We stacked the signal by groups of a few tens of lines to improve the quality of our fitting process. On both sources we reached significantly higher S/N and spectral resolution than the most recent detections by the LOw Frequency ARray (LOFAR). The variation of line shape with n provides constraints on the physical properties of the clouds: T_e, n_e, the temperature T_0 of the radiation field, the mean turbulent velocity v_t and the typical size of the cloud. The NenuFAR observations sample a larger space volume than LOFAR's towards the same sources due to the differences in instrumental beamsizes, and the discrepancies highlight the sensitivity of low-frequency CRRLs as probes of the diffuse ISM, paving the way towards large area surveys of CRRLs in our Galaxy.

astro-ph.GA↗

arXiv2025

Comparing the morphology of molecular clouds without supervision

Molecular clouds show complex structures reflecting their non-linear dynamics. Many studies investigating the bridge between their morphology and physical properties have shown the value of non-Gaussian higher-order statistics in capturing physical information. Yet, as this bridge is usually characterized in the supervised world of simulations, transferring it to observations can be hazardous, especially when the discrepancy between simulations and observations remains unknown. In this paper, we aim to identify relevant summary statistics, directly from the observation data. To do so, we developed a test to compare the informative power of two sets of summary statistics for a given unlabeled dataset. Contrary to supervised approaches, this test does not require knowledge of any class label or parameter associated with the data. Instead, it evaluates and compares the degeneracy levels of the summary statistics based on a notion of statistical compatibility. We applied this test to column density maps of 14 nearby molecular clouds observed by Herschel and iteratively compared different sets of typical summary statistics. We show that a standard Gaussian description of these clouds is highly degenerate but can be substantially improved when being estimated on the logarithm of the maps. This illustrates that low-order statistics, when properly used, remain very powerful. We further show that such descriptions still exhibit a small quantity of degeneracies, some of which are lifted by the higher-order statistics provided by reduced wavelet scattering transforms. These degeneracies quantitatively differ between observations and state-of-the-art simulations of dense cloud collapse, and they are not present for logFBM models. Finally, we show how to cooperatively use the summary statistics identified to build a morphological distance, which is evaluated visually and gives convincing results.

astro-ph.GA↗

arXiv2025

Unveiling two deeply embedded young protostars in the S68N Class 0 protostellar core with JWST/NIRSpec

The near-infrared (NIR) emission of the youngest protostars still needs to be characterized to better understand the evolution of their accretion and ejection activity. We analyze James Webb Space Telescope NIRSpec 1.7 -- 5.3 $μ$m observations of two deeply embedded sources in the S68N protostellar core in Serpens. The North Central (NC) source exhibits a highly obscured spectrum (A_K ~ 4.8 mag) that is modeled with a pre-main-sequence photosphere and a hot disk component. The photospheric parameters are consistent with a young, low-mass photosphere, as suggested by the low surface gravity, log g of 1.95 $\pm$ 0.15 cm s$^{-2}$. The hot disk suggests that accretion onto the central protostellar embryo is ongoing, although prototypical accretion-tracing emission lines HI are not detected. The South Central (SC) source, which is even more embedded (A_K ~ 8 mag; no continuum is detected shortward of 3.6 $μ$m) appears to be driving the large-scale S68N protostellar outflow, and launches a collimated hot molecular jet detected in \Ht and CO ro-vibrational lines. Shock modeling of the \Ht (ro)vibrational lines establishes that fast $C$-type shocks ($\geq$ 30 km s$^{-1}$), with high pre-shock density ($\geq$ $10^7$ cm$^{-3}$), and strong magnetic field (b ~ 3--10, where $B = b\,\times\,\sqrt{\textrm{n}_{\textrm{H}} (\textrm{cm}^{-3})}\,μ\textrm{G}$) best match the data. The bright CO fundamental line forest suggests energetic excitation, with the contribution of non-LTE effects, ie irradiation pumping. Detected OH and CH$^{+}$ ro-vibrational lines support this hypothesis. These two Class 0 protostars seem to be in very young evolutionary stages and still have to acquire the bulk of their final stellar masses. These results demonstrate that JWST enables unprecedented diagnostics of these first stages of the protostellar evolutionary phase.

astro-ph.SR↗

arXiv2024

Supernova Shocks in Molecular Clouds: Shocks Driven into Dense Cores in IC 443 and 3C 391

Supernova shocks into dense molecular cores in IC 443 (clumps B, C, and G) and 3C 391 were observed using the Stratospheric Observatory for Infrared Astronomy and complemented by archival data from the Herschel Space Observatory. The pure rotational transitions 0-0 S(1) and S(5) of H2, and the ground-state 110-101 transition of H2O, are all broadened, arising from molecules that survive the passage of the shock front. Theoretical models from the Paris-Durham shock code were analyzed to generate synthetic profiles that approximately match the observations. The observations can be fit with two shock conditions, which approximate the range of densities in the pre-shock molecular cloud. The width and brightness of the S(5) lines require shocks into gas with a density of order 2,000 cm-3, into which the IC 443 blast wave drives shocks with speed 60 km/s. The brightness and narrower width of the S(1) lines requires different shocks, into gas with density of order 10^5 cm-3, with shock speeds of 10 km/s. The H2O velocity distribution is also consistent with these shocks. The existence of shocks into dense gas shows that the bright shocked clumps in IC~443 were prestellar cores. It is unlikely that they will form stars soon after the passage of the shock front, given the input of kinetic and thermal energy from the shocks.

astro-ph.GA↗

arXiv2024

Physical conditions in Centaurus A's northern filaments II: Does the HCO$^+$ emission highlight the presence of shocks?

Abridged: We present the first observation of the HCO+(1-0) and HCN(1-0) emission in the northern filaments of Centaurus A with ALMA. HCO+(1-0) is detected in 9 clumps of the Horseshoe complex, with similar velocities as the CO(1-0) emission. Conversely, the HCN(1-0) is not detected and we derive upper limits on the flux. At a resolution of ~40 pc, the line ratio of the velocity-integrated intensities I_HCO+/I_CO varies between 0.03 and 0.08, while I_HCO+/I_HCN is higher than unity with an average lower limit of 1.51. These ratios are significantly higher than what is observed in nearby star-forming galaxies. Moreover, the ratio I_HCO+/I_CO decreases with increasing CO integrated intensity, contrary to what is observed in the star-forming galaxies. This indicates that the HCO+ emission is enhanced and may not arise from dense gas within the Horseshoe complex. This hypothesis is strengthened by the average line ratio I_HCN/I_CO<0.03 which suggests that the gas density is rather low. Using non-LTE, large velocity gradient modelling with RADEX, we explored two possible phases of the gas, that we call "diffuse" and "dense", and are characterised by a significant difference in the HCO+ relative abundance to CO, respectively N_HCO+/N_CO=10^-3 and 3x10^-5. The average CO(1-0) and HCO+(1-0) integrated intensities and the upper limit on HCN(1-0) are compatible with both "diffuse" and "dense" gas. The spectral setup of the present observations also covers the SiO(2-1). While undetected, the upper limit on SiO(2-1) is not compatible with the RADEX predictions for the "dense" gas. We conclude that the 9 molecular clouds detected in HCO+(1-0) are likely dominated by diffuse molecular gas. While the exact origin of the HCO+(1-0) emission remains to be investigated, it is likely related to the energy injection within the molecular gas that prevents gravitational collapse and star formation.

astro-ph.GA↗

arXiv2024

SOFIA/EXES observations of warm H2 at high spectral resolution: II. IC443C, NGC2071, and 3C391

Using the EXES instrument on SOFIA, we have obtained velocity-resolved spectra of several pure rotational lines of H2 toward shocked molecular gas within three Galactic sources: the supernova remnant (SNR) IC443 (Clump C), a protostellar outflow in the intermediate-mass star-forming region NGC 2071, and the SNR 3C391. These observations had the goal of searching for expected velocity shifts between ortho- and para-H2 transitions emitted by C-type shocks. In contrast in our previous similar study of HH7, the result of our search was negative: no velocity shifts were reliably detected. Several possible explanations for the absence of such shifts are discussed: these include a preshock ortho-to-para ratio that is already close to the high-temperature equilibrium value of 3 (in the case of IC443C), the more complex shock structures evident in all these sources, and the larger projected aperture sizes relative to those in the observations of HH7.

astro-ph.GA↗

arXiv2024

ALMA-IMF XIV: Free-Free Templates Derived from H$41α$ and Ionized Gas Content in Fifteen Massive Protoclusters

We use the H$41α$ recombination line to create templates of the millimeter free-free emission in the ALMA-IMF continuum maps, which allows to separate it from dust emission. This method complements spectral-index information and extrapolation from centimeter wavelength maps. We use the derived maps to estimate the properties of up to 34 HII regions across the ALMA-IMF protoclusters. The hydrogen ionizing-photon rate $Q_0$ and spectral types follow the evolutionary trend proposed by Motte et al. The youngest protoclusters lack detectable ionized gas, followed by protoclusters with increasing numbers of OB stars. The total $Q_0$ increases from $\sim 10^{45}$ s$^{-1}$ to $> 10^{49}$ s$^{-1}$. We used the adjacent He$41α$ line to measure the relative number abundances of helium, finding values consistent with the Galactic interstellar medium, although a few outliers are discussed. A search for sites of maser amplification of the H$41α$ line returned negative results. We looked for possible correlations between the electron densities ($n_e$), emission measures (EM), and $Q_0$ with HII region size $D$. The latter are the better correlated, with $Q_0 \propto D^{2.49\pm0.18}$. This favors interpretations where smaller ultracompact HII regions are not necessarily the less dynamically evolved versions of larger ones, but rather are ionized by less massive stars. Moderate correlations were found between dynamical width $ΔV_\mathrm{dyn}$ with $D$ and $Q_0$. $ΔV_\mathrm{dyn}$ increases from about one to two times the ionized-gas sound speed. Finally, an outlier HII region south of W43-MM2 is discussed. We suggest that this source could harbor an embedded stellar or disk wind.

astro-ph.GA↗

arXiv2024

PDRs4All VIII: Mid-IR emission line inventory of the Orion Bar

Mid-infrared emission features probe the properties of ionized gas, and hot or warm molecular gas. The Orion Bar is a frequently studied photodissociation region (PDR) containing large amounts of gas under these conditions, and was observed with the MIRI IFU aboard JWST as part of the "PDRs4All" program. The resulting IR spectroscopic images of high angular resolution (0.2") reveal a rich observational inventory of mid-IR emission lines, and spatially resolve the substructure of the PDR, with a mosaic cutting perpendicularly across the ionization front and three dissociation fronts. We extracted five spectra that represent the ionized, atomic, and molecular gas layers, and measured the most prominent gas emission lines. An initial analysis summarizes the physical conditions of the gas and the potential of these data. We identified around 100 lines, report an additional 18 lines that remain unidentified, and measured the line intensities and central wavelengths. The H I recombination lines originating from the ionized gas layer bordering the PDR, have intensity ratios that are well matched by emissivity coefficients from H recombination theory, but deviate up to 10% due contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni, and show how certain line ratios vary between the five regions. We observe the pure-rotational H$_2$ lines in the vibrational ground state from 0-0 S(1) to 0-0 S(8), and in the first vibrationally excited state from 1-1 S(5) to 1-1 S(9). We derive H$_2$ excitation diagrams, and approximate the excitation with one thermal (~700 K) component representative of an average gas temperature, and one non-thermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model for the Orion Bar PDR and highlight the differences with the observations.

astro-ph.GA↗

arXiv2024

A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk

Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photo-dissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, impacting planet formation within the disks. We report JWST and Atacama Large Millimetere Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modelling their kinematics and excitation allows us to constrain the physical conditions within the gas. We quantify the mass-loss rate induced by the FUV irradiation, finding it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk.

astro-ph.GA↗

arXiv2024

Cosmic-ray induced ionization rates and non-thermal emissions from nuclei of starburst galaxies

Cosmic rays are the only agent capable of ionizing the interior of dense molecular clouds and, thus, they are believed to play an essential role in determining the physical and chemical evolution of star-forming regions. In this work, we aim to study cosmic-ray induced ionization rates in starburst environments using non-thermal emissions of cosmic rays from starburst nuclei. To this end, we first revisit cosmic-ray models which could explain data of non-thermal emissions from radio to X-ray and gamma-ray from nuclei of three prototypical starburst galaxies NGC 253, M82, and Arp 220. These models are then applied to predict ionization rates in starburst environments which gives values around $10^{-14}$ s$^{-1}$. Such a high value of the ionization rate, which is 2 to 3 orders of magnitude higher than the typical values found in the Milky Way, is probably due to relatively high rates of supernova explosions occurring within the nuclei of these starburst galaxies. We also discuss in more details the case of NGC 253 where our predicted ionization rate is found to be, in most cases, a few times smaller than the values inferred from molecular line observations of clouds in the starburst nucleus. The general framework provided in this work illustrates how the use of non-thermal emission data could help to provide more insights into ionization rates or, more generally, cosmic-ray impact in starburst environments.

astro-ph.HE↗

arXiv2023

ALMA-IMF VIII -- Combination of Interferometric Continuum Images with Single-Dish Surveys and Structural Analysis of Six Protoclusters

We present the combination of ALMA-IMF and single-dish continuum images from the Mustang-2 Galactic Plane Survey (MGPS90) at 3 millimeters and the Bolocam Galactic Plane Survey (BGPS) at 1 millimeter. Six and ten out of the fiffteen ALMA-IMF fields are combined with MGPS90 and BGPS, respectively. The combination is made via the feathering technique. We used the dendrogram algorithm throughout the combined images, and performed further analysis in the six fields with combination in both bands (G012.80, W43-MM1, W43-MM2, W43-MM3, W51-E, W51-IRS2). In these fields, we calculated spectral index maps and used them to separate regions dominated by dust or free-free emission, and then performed further structural analysis. We report the basic physical parameters of the dust-dominated (column densities, masses) and ionized (emission measures, hydrogen ionization photon rates) structures. We also searched for multi-scale relations in the dust-dominated structures across the analyzed fields, finding that the fraction of mass in dendrogram leaves (which we label as "Leaf Mass Eficiency", LME) as a function of molecular gas column density follows a similar trend: a rapid, exponential-like growth, with maximum values approaching 100% in most cases. The observed behaviour of the LME with gas column is tentatively interpreted as an indicator of large star formation activity within the ALMA-IMF protoclusters. W51-E and G012.80 stand out as cases with comparatively large and reduced potential for further star formation, respectively.

astro-ph.GA↗

arXiv2023

PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar

(Abridged) We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the HII region to the atomic PDR (crossing the ionisation front (IF)), and the subsequent transition to the molecular PDR (crossing the dissociation front (DF)). We use high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science Program. The NIRSpec data reveal a forest of lines including, but not limited to, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescence lines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, and their CD counterparts), CO2 ice, pure rotational and ro-vibrational lines from H2, and ro-vibrational lines HD, CO, and CH+, most of them detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. We observe numerous smaller scale structures whose typical size decreases with distance from Ori C and IR lines from CI, if solely arising from radiative recombination and cascade, reveal very high gas temperatures consistent with the hot irradiated surface of small-scale dense clumps deep inside the PDR. The H2 lines reveal multiple, prominent filaments which exhibit different characteristics. This leaves the impression of a "terraced" transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star- and planet formation as well as galaxy evolution.

astro-ph.GA↗

arXiv2023

PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 $μ$m. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR, the atomic PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extract five template spectra to represent the morphology and environment of the Orion Bar PDR. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. While the spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 $μ$m, a wealth of weaker features and sub-components are present. We report trends in the widths and relative strengths of AIBs across the five template spectra. These trends yield valuable insight into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 $μ$m AIB emission from class B$_{11.2}$ in the molecular PDR to class A$_{11.2}$ in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a "weeding out" of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called 'grandPAHs'.

astro-ph.GA↗

arXiv2023

PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula

The JWST has captured the most detailed and sharpest infrared images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR). We investigate the fundamental interaction of far-ultraviolet photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of 0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. A complex, structured, and folded DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate.

astro-ph.GA↗

arXiv2023

Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance

Interstellar shocks, a key element of stellar feedback processes, shape the structure of the interstellar medium (ISM) and are essential for the chemistry, thermodynamics, and kinematics of interstellar gas. Powerful, high-velocity shocks are driven by stellar winds, young supernova explosions, more evolved supernova remnants, cloud-cloud collisions, and protostellar outflows, whereas the existence and origin of much-lower-velocity shocks ($\lesssim $ 10 km$~$s$^{-1}$) are not understood. Direct observational evidence for interstellar shocks in diffuse and translucent ISM environments have been especially lacking. We present the most sensitive survey to date of SiO -- often considered an unambiguous tracer of interstellar shocks -- in absorption, obtained with the Northern Extended Millimeter Array interferometer. We detect SiO in 5/8 directions probing diffuse and translucent environments without ongoing star formation. Our results demonstrate that SiO formation in the diffuse ISM (i.e., in the absence of significant star formation and stellar feedback) is more widespread and effective than previously reported. The observed SiO linewidths are all $\lesssim$ 4 km$~$s$^{-1}$, excluding high-velocity shocks as a formation mechanism. Yet, the SiO abundances we detect are mostly 1 to 2 orders of magnitude higher than typically assumed in quiescent environments and are often accompanied with other molecular transitions whose column densities cannot be explained with UV-dominated chemical models. Our results challenge the traditional view of SiO production via stellar-feedback sources and emphasize the need for observational constraints on the distribution of Si in the gas phase and grain mantles, which are crucial for understanding the physics of grain processing and diffuse interstellar chemistry.

astro-ph.GA↗