arXiv subjects

C. Gieser

Publications and source records attributed to C. Gieser.

At least 37 records · Page 2Linked to original sources

arXiv2025

PRODIGE - envelope to disk with NOEMA: V. Low 12C/13C ratios for CH3OH and CH3CN in hot corinos

The 12C/13C isotope ratio has been derived towards numerous cold clouds (20-50 K) and a couple protoplanetary disks and exoplanet atmospheres. However, direct measurements of this ratio in the warm gas (>100 K) around young low-mass protostars remain scarce, but are required to study its evolution during star and planet formation. We derived 12C/13C ratios from the isotopologues of the complex organic molecules (COMs) CH3OH and CH3CN in the warm gas towards seven Class 0/I protostellar systems to improve our understanding of the evolution of the 12C/13C ratios during star and planet formation. We used the data that were taken as part of the PRODIGE large program with the NOEMA at 1mm. The emission of CH3OH and CH3CN is spatially unresolved in the PRODIGE data (300au scale). Derived rotational temperatures exceed 100K, telling us that they trace the gas of the hot corino, where CH3CN probes hotter regions than CH3OH on average (290 K versus 180 K). The column density ratios between the 12C and 13C isotopologues, derived from LTE analysis, range from 4 to 30, thus, are significantly lower than the expected local ISM isotope ratio of about 68. Assuming that CH3CN and CH3OH may inherit the 12C/13C ratio from their precursor species, astrochemical models were conducted for the latter and compared with our observational results. We conclude that an enrichment in 13C in COMs at the earliest protostellar stages is likely inherited from the COMs' precursor species, whose 12C/13C ratios are set during the prestellar stage via isotopic exchange reactions. This also implies that low 12C/13C ratios observed at later evolutionary stages could at least partially be inherited. A final conclusion on 12C/13C ratios in protostellar environments requires improved observations to tackle current observational limitations and additional modelling efforts.

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arXiv2025

Resolved Gas Temperatures and 12C/13C ratios in SVS13A from ALMA Observations of CH3CN and CH3-13-CN

Context. Multiple systems are common in field stars, and the frequency is found to be higher in early evolutionary stages. Thus, the study of young multiple systems during the embedded stages is key to have a comprehensive understanding of star formation. In particular, how material accretes from the large-scale envelope into the inner region and how this flow interacts with the system physically and chemically has not yet been well characterized observationally. Aims. We aim to provide a snapshot of the forming protobinary system SVS13A, consisting of VLA4A and VLA4B. This includes clear pictures of its kinematic structures, physical conditions, and chemical properties. Methods. We conducted ALMA observations toward SVS13A targeting CH3CN and CH3-13CN J=12-11 K-ladder line emission with a high spatial resolution of ~30 au at a spectral resolution of ~0.08 km s-1 Results. We perform LTE radiative transfer models to fit the spectral features of the line emission. We find the two-layer LTE radiative model including dust absorption is essential to interpret the CH3CN and CH3-13-CN line emission. We identify two major and four small kinematic components, and derive their physical and chemical properties. Conclusions. We find a possible infalling signature toward the bursting secondary source VLA4A, which may be fed by an infalling streamer from the large-scale envelope. The mechanical heating in the binary system, as well as the infalling shocked gas, likely play a role in the thermal structure of the protobinary system. By accumulating mass from the streamer, the system might have experienced a gravitationally unstable phase before the accretion outburst. Finally, the derived CH3CN/CH3-13-CN ratio is lower than the canonical ratio in the ISM and is different between VLA4A and VLA4B.

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arXiv2025

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE. IV. Unveiling the hidden structures in DR18

The Cygnus-X complex is a massive, nearby (1.4 kpc) star-forming region with several OB associations. As part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program, we carried out 3.6 millimeter (mm) continuum and spectral line high-resolution observations ($\sim$ 3 - 4$''$) toward DR18, covering several molecular species with the Northern Extended Millimeter Array (NOEMA) and the Institut de Radioastronomie Millimétrique (IRAM) 30m telescope. In addition, multi-wavelength archival datasets were used to provide a comprehensive analysis of the region. A comparison of the 3.6mm and 6 cm continuum emission confirms that a B2 star (DR18-05) shapes the cometary HII region in the DR18 cavity, with ionized gas escaping toward the OB2 association. On the other hand, the extended 3.6mm and 6 cm continuum emission are likely to trace photoevaporating ionized gas from ultraviolet radiation from the Cyg OB2 association, not from DR18-05. The shell structure around DR18-05 indicates photodissociation regions (PDRs) formed by the expanding HII region and photo-erosion from DR18-05 and OB2 stars. We also identified 18 compact cores with N$_2$H$^+$ emission, half of which are gravitationally bound and mostly located in colder regions behind the PDRs. The SiO emission is found only in PDRs, with narrow-line widths ( 0.8 - 2.0 km s$^{-1}$) and lower abundances (X(SiO) $\sim$ 5$\times$10$^{-11}$ - 1$\times$10$^{-10}$). Comparing with the UV irradiated shock models, we suggest that the SiO emission partially encompassing the HII region arises from the molecular gas region, marginally compressed by low-velocity shocks with $\sim$ 5 km s$^{-1}$, irradiated by external UV radiation (G$_{\rm 0} \sim 10^{2} - 10^{3}$), as they traverse through a medium with $n_{\rm H} \sim 10^{4}$ to 10$^5$ cm$^{-3}$.

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arXiv2025

JOYS: The [D/H] abundance derived from protostellar outflows across the Galactic disk measured with JWST

The total deuterium abundance [D/H] in the universe is set by just two processes: the creation of deuterium in Big Bang Nucleosynthesis at an abundance of [D/H]$=2.58\pm0.13\times10^{-5}$, and its destruction within stellar interiors. Measurements of the total [D/H] abundance can potentially provide a probe of Galactic chemical evolution, however, most measurements of [D/H] are only sensitive to the gas-phase deuterium, and the amount of deuterium sequestered in carbonaceous dust grains is debated. With the launch of JWST, it is now possible to measure the gas-phase [D/H] at unprecedented sensitivity and distances through observation of mid-IR lines of H$_2$ and HD. We employ data from the JWST Observations of Young protoStars (JOYS) program to measure the gas-phase [D/H] abundance with a rotation diagram analysis towards 5 nearby low-mass and 5 distant high-mass protostellar outflows. The gas-phase [D/H] varies between low-mass sources by up to a factor of $\sim4$, despite these sources likely having formed in a region of the Galactic disk that would be expected to have nearly constant total [D/H]. Most measurements of gas-phase [D/H] from our work or previous studies produce [D/H] $\lesssim 1.0\times10^{-5}$, a factor of $2-4$ lower than found from local UV absorption lines and as expected from Galactic chemical evolution models. The variations in [D/H] between our low-mass sources and the low [D/H] with respect to Galactic chemical evolution models suggest that our observations are not sensitive to the total [D/H]. Significant depletion of deuterium onto carbonaceous dust grains is a possible explanation, and tentative evidence of enhanced [D/H] towards shock positions with higher gas-phase Fe abundance is seen in the HH 211 outflow. Deeper observations of HD and H$_2$ in shocked environments and modelling of dust-grain destruction are warranted to test for the effects of depletion.

astro-ph.GA↗

arXiv2024

PRODIGE -- envelope to disk with NOEMA. IV. An infalling gas bridge surrounding two Class 0/I systems in L1448N

Context. The formation of stars has been subject to extensive studies in the past decades from molecular cloud to protoplanetary disk scales. It is still not fully understood how the surrounding material in a protostellar system, that often shows asymmetric structures with complex kinematic properties, feeds the central protostar(s) and their disk(s). Aims. We study the spatial morphology and kinematic properties of the molecular gas surrounding the IRS3A and IRS3B protostellar systems in the L1448N region located in the Perseus molecular cloud. Methods. We present 1 mm NOEMA observations of the PRODIGE large program and analyze the kinematic properties of molecular lines. Given the complexity of the spectral profiles, the lines are fitted with up to three Gaussian velocity components. The clustering algorithm DBSCAN is used to disentangle the velocity components into the underlying physical structure. Results. We discover an extended gas bridge (~3000 au) surrounding both the IRS3A and IRS3B systems in six molecular line tracers (C18O, SO, DCN, H2CO, HC3N, and CH3OH). This gas bridge is oriented along the northeast-southwest direction and shows clear velocity gradients on the order of 100 km/s/pc towards the IRS3A system. We find that the observed velocity profile is consistent with analytical streamline models of gravitational infall towards IRS3A. The high-velocity C18O (2-1) emission towards IRS3A indicates a protostellar mass of ~1.2 Msun. Conclusions. While high angular resolution continuum data often show IRS3A and IRS3B in isolation, molecular gas observations reveal that these systems are still embedded within a large-scale mass reservoir with a complex spatial morphology as well as velocity profiles. The kinematic properties of the extended gas bridge are consistent with gravitational infall toward the IRS3A protostar.

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arXiv2024

JWST Observations of Young protoStars (JOYS). Overview of gaseous molecular emission and absorption in low-mass protostars

The MIRI-MRS instrument onboard JWST allows for probing the molecular gas composition at mid-IR wavelengths at unprecedented resolution and sensitivity. It is important to study these features in low-mass embedded protostellar systems since the formation of planets is thought to start in this phase. We present JWST/MIRI-MRS data of 18 low-mass protostellar systems in the JOYS program, focusing on gas-phase molecular lines in spectra extracted from the central protostellar positions. Besides H2, the most commonly detected molecules are H2O, CO2, CO, and OH. Other molecules such as 13CO2, C2H2, 13CCH, HCN, C4H2, CH4, and SO2 are detected only toward at most three of the sources. The JOYS data also yield the surprising detection of SiO gas toward two sources (BHR71-IRS1, L1448-mm) and for the first time CS and NH3 at mid-IR wavelengths toward a low-mass protostar (B1-c). The temperatures derived for the majority of the molecules are 100-300 K, much lower than what is typically derived toward more evolved Class II sources (>500 K). Toward three sources (e.g., TMC1-W), hot (~1000 K) H2O is detected, indicative of the presence of hot molecular gas in the embedded disks, but such warm emission from other molecules is absent. The agreement in abundance ratios with respect to H2O between ice and gas point toward ice sublimation in a hot core for a few sources (e.g., B1-c) whereas their disagreement and velocity offsets hint at high-temperature (shocked) conditions toward other sources (e.g., L1448-mm, BHR71-IRS1). The typical temperatures of the gas-phase molecules of 100-300 K are consistent with both ice sublimation in hot cores as well as high-temperature gas phase chemistry. Molecular features originating from the inner embedded disks are not commonly detected, likely because they are too extincted even at mid-IR wavelengths by small not-settled dust grains in upper layers of the disk.

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arXiv2024

JWST Observations of Young protoStars (JOYS). HH 211: the textbook case of a protostellar jet and outflow

We use the James Webb Space Telescope (JWST) and its Mid-Infrared Instrument (MIRI) (5-28 um), to study the embedded HH 211 flow. We map a 0.95'x0.22' region, covering the full extent of the blue-shifted lobe, the central protostellar region, and a small portion of the red-shifted lobe. The jet driving source is not detected even at the longest mid-IR wavelengths. The overall morphology of the flow consists of a highly collimated jet, mostly molecular (H2, HD) with an inner atomic ([FeI], [FeII], [SI], [NiII]) structure. The jet shocks the ambient medium, producing several large bow-shocks, rich in forbidden atomic and molecular lines, and is driving an H2 molecular outflow, mostly traced by low-J, v=0 transitions. Moreover, 0-0 S(1) uncollimated emission is also detected down to 2"-3" (~650-1000 au) from the source, tracing a cold (T=200-400 K), less dense and poorly collimated molecular wind. The atomic jet ([FeII] at 26 um) is detected down to ~130 au from source, whereas the lack of H2 emission close to the source is likely due to the large visual extinction. Dust continuum-emission is detected at the terminal bow-shocks, and in the blue- and red-shifted jet, being likely dust lifted from the disk. The jet shows an onion-like structure, with layers of different size, velocity, temperature, and chemical composition. Moreover, moving from the inner jet to the outer bow-shocks, different physical, kinematic and excitation conditions for both molecular and atomic gas are observed. The jet mass-flux rate, momentum, and momentum flux of the warm H2 component are up to one order of magnitude higher than those inferred from the atomic jet component. Our findings indicate that the warm H2 component is the primary mover of the outflow, namely it is the most significant dynamical component of the jet, in contrast to jets from more evolved YSOs, where the atomic component is dominant.

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arXiv2024

Dynamical Accretion Flows -- ALMAGAL: Flows along filamentary structures in high-mass star-forming clusters

We use data from the ALMA Evolutionary Study of High Mass Protocluster Formation in the Galaxy (ALMAGAL) survey to study 100 ALMAGAL regions at $\sim$ 1 arsecond resolution located between $\sim$ 2 and 6 kpc distance. Using ALMAGAL $\sim$ 1.3mm line and continuum data we estimate flow rates onto individual cores. We focus specifically on flow rates along filamentary structures associated with these cores. Our primary analysis is centered around position velocity cuts in H$_2$CO (3$_{0,3}$ - 2$_{0,2}$) which allow us to measure the velocity fields, surrounding these cores. Combining this work with column density estimates we derive the flow rates along the extended filamentary structures associated with cores in these regions. We select a sample of 100 ALMAGAL regions covering four evolutionary stages from quiescent to protostellar, Young Stellar Objects (YSOs), and HII regions (25 each). Using dendrogram and line analysis, we identify a final sample of 182 cores in 87 regions. In this paper, we present 728 flow rates for our sample (4 per core), analysed in the context of evolutionary stage, distance from the core, and core mass. On average, for the whole sample, we derive flow rates on the order of $\sim$10$^{-4}$ M$_{sun}$yr$^{-1}$ with estimated uncertainties of $\pm$50%. We see increasing differences in the values among evolutionary stages, most notably between the less evolved (quiescent/protostellar) and more evolved (YSO/HII region) sources. We also see an increasing trend as we move further away from the centre of these cores. We also find a clear relationship between the flow rates and core masses $\sim$M$^{2/3}$ which is in line with the result expected from the tidal-lobe accretion mechanism. Overall, we see increasing trends in the relationships between the flow rate and the three investigated parameters; evolutionary stage, distance from the core, and core mass.

astro-ph.GA↗

arXiv2024

JOYS+: link between ice and gas of complex organic molecules. Comparing JWST and ALMA data of two low-mass protostars

A rich inventory of complex organic molecules (COMs) has been observed in high abundances in the gas phase toward Class 0 protostars. These molecules are suggested to be formed in ices and sublimate in the warm inner envelope close to the protostar. However, only the most abundant COM, methanol (CH3OH), has been firmly detected in ices before the era of James Webb Space Telescope (JWST). Now it is possible to detect the interstellar ices of other COMs and constrain their ice column densities quantitatively. We aim to determine the column densities of several oxygen-bearing COMs (O-COMs) in both gas and ice for two low-mass protostellar sources, NGC 1333 IRAS 2A and B1-c, as case studies in our JWST Observations of Young protoStars (JOYS+) program. By comparing the column density ratios w.r.t. CH3OH between both phases measured in the same sources, we can probe into the evolution of COMs from ice to gas in the early stages of star formation. We are able to fit the fingerprints range of COM ices between 6.8 and 8.8 um in the JWST/MIRI-MRS spectra of B1-c using similar components as recently used for IRAS 2A. We claim detection of CH4, OCN-, HCOO-, HCOOH, CH3CHO, C2H5OH, CH3OCH3, CH3OCHO, and CH3COCH3 in B1-c, and upper limits are estimated for SO2, CH3COOH, and CH3CN. The comparison of O-COM ratios w.r.t CH3OH between ice and gas shows two different cases. 1) the column density ratios of CH3OCHO and CH3OCH3 match well between the two phases, which may be attributed to a direct inheritance from ice to gas or strong chemical links with CH3OH. 2) the ice ratios of CH3CHO and C2H5OH w.r.t. CH3OH are higher than the gas ratios by 1-2 orders of magnitudes. This difference can be explained by the gas-phase reprocessing following sublimation, or different spatial distributions of COMs in the envelope.

astro-ph.GA↗

arXiv2024

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE III. The large scale distribution of DCO+, DNC and DCN in the DR21 filament

Deuterated molecules and their molecular D/H-ratios (RD(D)) are important diagnostic tools to study the physical conditions of star-forming regions. The degree of deuteration, RD(D), can be significantly enhanced over the elemental D/H-ratio depending on physical parameters. Within the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE), we aim to explore the large-scale distribution of deuterated molecules in the nearby Cygnus-X region. We focus on the analysis of large-scale structures of deuterated molecules in the filamentary region hosting the prominent Hii region DR21 and DR21(OH). Here we discuss the HCO+, HNC and HCN molecules and their deuterated isotopologues DCO+, DNC and DCN. The spatial distributions of integrated line emissions from DCO+, DNC, and DCN reveal morphological differences. DCO+ displays the most extended emission, characterized by several prominent peaks. Likewise, DNC exhibits multiple peaks, although its emission appears less extended compared to DCO+. In contrast to the extended emission of DCO+ and DNC, DCN appears the least extended, with distinct peaks. Focusing only on the regions where all three molecules are observed, the mean deuteration ratios for each species are 0.01 for both DNC and DCN, and = 0.005 for DCO+. Anti-correlations are found with deuterated molecules and dust temperature or N(H2). The strongest anti-correlation is found with RD(DCO+) and N(H2). The anti-correlation of RD(DCO+) and N(H2) is suggested to be a result of a combination of an increased photodissociation degree and shocks. A strong positive correlation between the ratio of integrated intensities of DCN and DNC with their 13C-isotopologues, are found in high column density regions. The positive relationship between the ratios implies that the D-isotopologue of the isomers could potentially serve as a tracer for the kinetic gas temperature.

astro-ph.GA↗

arXiv2024

PRODIGE -- Envelope to Disk with NOEMA III. The origin of complex organic molecule emission in SVS13A

Complex Organic Molecules (COMs) have been found toward low-mass protostars but the origins of the COM emission are still unclear. It can be associated with, for example, hot corinos, outflows, and/or accretion shock/disk atmosphere. We have conducted NOEMA observations toward SVS13A from the PROtostars & DIsks: Global Evolution (PRODIGE) program. Our previous \ce{DCN} observations reveal a possible infalling streamer, which may affect the chemistry of the central protobinary by inducing accretion outbursts and/or shocked gas. Here, we further analyze six O-bearing COMs: CH3OH, aGg'-(CH2OH)2, C2H5OH, CH2(OH)CHO, CH3CHO, and CH3OCHO. Although the COM emission is not spatially resolved, we constrain the source sizes to $\lesssim0.3-0.4$ arcsec (90$-$120 au) by conducting uv-domain Gaussian fitting. Interestingly, the high-spectral resolution data reveal complex line profiles with multiple peaks showing differences between these six O-bearing COMs. The LTE fitting unveils differences in excitation temperatures and emitting areas among these COMs. We further conduct multiple-velocity-component LTE fitting to decompose the line emission into different kinematic components. Up to 6 velocity components are found from the LTE modeling. The temperature, column density, and source size of these components from each COM are obtained. We find a variety in excitation temperatures ($100-500$ K) and source sizes (D$\sim10-70$ au) from these kinematic components from different COMs. The emission of each COM can trace several components and different COMs most likely trace different regions. Given this complex structure, we suggest that the central region is inhomogeneous and unlikely to be heated by only protostellar radiation. We conclude that accretion shocks induced by the large-scale infalling streamer likely exist and contribute to the complexity of the COM emission.

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arXiv2024

PRODIGE -- Planet-forming disks in Taurus with NOEMA. I. Overview and first results for 12CO, 13CO, and C18O

We are performing a line survey of 8 planet-forming Class II disks in Taurus with the IRAM NOrthern Extended Millimeter Array (NOEMA), as a part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution; PIs: P. Caselli and Th. Henning). Compact and extended disks around T Tauri stars CI, CY, DG, DL, DM, DN, IQ Tau, and UZ Tau E are observed in ~80 lines from >20 C-, O,- N-, and S-bearing species. The observations in four spectral settings at 210-280 GHz with $1σ$ rms sensitivity of ~ 8-12 mJy/beam at 0.9" and 0.3 km/s resolution will be completed in 2024. The uv-visibilities are fitted with the DiskFit model to obtain key stellar and disk properties. In this paper, the combined $^{12}$CO, $^{13}$CO and C$^{18}$O $J = 2-1$ data are presented. We find that the CO fluxes and disk masses inferred from dust continuum tentatively correlate with the CO emission sizes. We constrain dynamical stellar masses, geometries, temperatures, the CO column densities and gas masses for each disk. The best-fit temperatures at 100 au are ~ 17-37 K, and decrease radially with the power-law exponent q ~ 0.05-0.76. The inferred CO column densities decrease radially with the power-law exponent p ~ 0.2-3.1. The gas masses estimated from $^{13}$CO (2-1) are ~ $0.001-0.2 M_\textrm{Sun}$. The best-fit CO column densities point to severe CO freeze-out in the disks. The DL Tau disk is an outlier, and has either stronger CO depletion or lower gas mass than the rest of the sample. The CO isotopologue ratios are roughly consistent with the observed values in disks and the low-mass star-forming regions.

astro-ph.GA↗

arXiv2024

JOYS: MIRI/MRS spectroscopy of gas-phase molecules from the high-mass star-forming region IRAS 23385+6053

Space-based mid-IR spectroscopy provides tracers of warm gas in star-forming regions that are inaccessible from the ground. Past mid-IR spectra of bright high-mass protostars in the hot-core phase typically showed strong absorption features from molecules such as CO$_2$, C$_2$H$_2$, and HCN. However, little is known about their fainter counterparts at earlier stages. We thus aim to characterize the gas-phase molecular features in JWST MIRI/MRS observations of the young high-mass star-forming region IRAS 23385+6053. Spectra were extracted from two mid-IR sources and three H$_2$ bright outflow knots in the MIRI/MRS field of view. Rich molecular spectra with emission from CO, H$_2$, HD, H$_2$O, C$_2$H$_2$, HCN, CO$_2$, and OH are detected towards the two mid-IR sources. However, only CO and OH are seen towards the brightest H$_2$ knots, suggesting that the majority of the observed species are associated with disks or hot core regions rather than outflows. Simple Local thermodynamic equilibrium (LTE) slab models were used to fit the observed molecular features. The LTE model fits to $^{12}$CO$_{2}$, C$_{2}$H$_{2}$, and HCN emission suggest warm $120-200$ K emission arising from a disk surface around one or both protostars. Weak $\sim500$ K H$_2$O emission at $\sim$ 6-7 $μ$m is detected towards one mid-IR source, whereas $250-1050$ K H$_2$O absorption is found in the other. The H$_2$O absorption may occur in the disk atmosphere due to strong accretion-heating of the midplane, or in a disk wind viewed at an ideal angle for absorption. CO emission may originate in the hot inner disk or outflow shocks. OH emission is likely excited in a non-LTE manner through water photodissociation or chemical formation. The observations are consistent with disks having already formed in the young IRAS 23385+6053 system, but further observations are needed to disentangle the effects of geometry and evolution.

astro-ph.GA↗

arXiv2023

JWST Observations of Young protoStars (JOYS+): Detection of icy complex organic molecules and ions. I. CH$_4$, SO$_2$, HCOO$^-$, OCN$^-$, H$_2$CO, HCOOH, CH$_3$CH$_2$OH, CH$_3$CHO, CH$_3$OCHO, CH$_3$COOH

Complex organic molecules (COMs) detected in the gas phase are thought to be mostly formed on icy grains, but no unambiguous detection of icy COMs larger than CH3OH has been reported so far. Exploring this matter in more detail has become possible with the JWST the critical 5-10 $μ$m range. In the JOYS+ program, more than 30 protostars are being observed with the MIRI/MRS. This study explores the COMs ice signatures in the low and high-mass protostar, IRAS 2A and IRAS 23385, respectively. We fit continuum and silicate subtracted observational data with IR laboratory ice spectra. We use the ENIIGMA fitting tool to find the best fit between the lab data and the observations and to performs statistical analysis of the solutions. We report the best fits for the spectral ranges between 6.8 and 8.6 $μ$m in IRAS 2A and IRAS 23385, originating from simple molecules, COMs, and negative ions. The strongest feature in this range (7.7 $μ$m) is dominated by CH4 and has contributions of SO2 and OCN-. Our results indicate that the 7.2 and 7.4 $μ$m bands are mostly dominated by HCOO-. We find statistically robust detections of COMs based on multiple bands, most notably CH3CHO, CH3CH2OH, and CH3OCHO. The likely detection of CH3COOH is also reported. The ice column density ratios between CH3CH2OH and CH3CHO of IRAS 2A and IRAS 23385, suggests that these COMs are formed on icy grains. Finally, the derived ice abundances for IRAS 2A correlate well with those in comet 67P/GC within a factor of 5. Based on the MIRI/MRS data, we conclude that COMs are present in interstellar ices, thus providing additional proof for a solid-state origin of these species in star-forming regions. The good correlation between the ice abundances in comet 67P and IRAS 2A is in line with the idea that cometary COMs can be inherited from the early protostellar phases.

astro-ph.SR↗

arXiv2023

JOYS+: mid-infrared detection of gas-phase SO$_2$ emission in a low-mass protostar. The case of NGC 1333 IRAS2A: hot core or accretion shock?

JWST/MIRI has sharpened our infrared eyes toward the star formation process. This paper presents the first mid-infrared detection of gaseous SO$_2$ emission in an embedded low-mass protostellar system. MIRI-MRS observations of the low-mass protostellar binary NGC 1333 IRAS2A are presented from the JWST Observations of Young protoStars (JOYS+) program, revealing emission from the SO$_2~ν_3$ asymmetric stretching mode at 7.35 micron. The results are compared to those derived from high-angular resolution SO$_2$ data obtained with ALMA. The SO$_2$ emission from the $ν_3$ band is predominantly located on $\sim50-100$ au scales around the main component of the binary, IRAS2A1. A rotational temperature of $92\pm8$ K is derived from the $ν_3$ lines. This is in good agreement with the rotational temperature derived from pure rotational lines in the vibrational ground state (i.e., $ν=0$) with ALMA ($104\pm5$ K). However, the emission of the $ν_3$ lines is not in LTE given that the total number of molecules predicted by a LTE model is found to be a factor $2\times10^4$ higher than what is derived for the $ν=0$ state. This difference can be explained by a vibrational temperature that is $\sim100$ K higher than the derived rotational temperature of the $ν=0$ state. The brightness temperature derived from the continuum around the $ν_3$ band of SO$_2$ is $\sim180$ K, which confirms that the $ν_3=1$ level is not collisionally populated but rather infrared pumped by scattered radiation. This is also consistent with the non-detection of the $ν_2$ bending mode at 18-20 micron. Given the rotational temperature, the extent of the emission ($\sim100$ au in radius), and the narrow line widths in the ALMA data (3.5 km/s), the SO$_2$ in IRAS2A likely originates from ice sublimation in the central hot core around the protostar rather than from an accretion shock at the disk-envelope boundary.

astro-ph.SR↗

arXiv2023

Density distributions, magnetic field structures and fragmentation in high-mass star formation

Methods: Observing the large pc-scale Stokes I mm dust continuum emission with the IRAM 30m telescope and the intermediate-scale (<0.1pc) polarized submm dust emission with the Submillimeter Array toward a sample of 20 high-mass star-forming regions allows us to quantify the dependence of the fragmentation behaviour of these regions depending on the density and magnetic field structures. Results: We infer density distributions n~r^{-p} of the regions with typical power-law slopes p around ~1.5. There is no obvious correlation between the power-law slopes of the density structures on larger clump scales (~1pc) and the number of fragments on smaller core scales (<0.1pc). Comparing the large-scale single-dish density profiles to those derived earlier from interferometric observations at smaller spatial scales, we find that the smaller-scale power-law slopes are steeper, typically around ~2.0. The flattening toward larger scales is consistent with the star-forming regions being embedded in larger cloud structures that do not decrease in density away from a particular core. Regarding the magnetic field, for several regions it appears aligned with filamentary structures leading toward the densest central cores. Furthermore, we find different polarization structures with some regions exhibiting central polarization holes whereas other regions show polarized emission also toward the central peak positions. Nevertheless, the polarized intensities are inversely related to the Stokes I intensities. We estimate magnetic field strengths between ~0.2 and ~4.5mG, and we find no clear correlation between magnetic field strength and the fragmentation level of the regions. Comparison of the turbulent to magnetic energies shows that they are of roughly equal importance in this sample. The mass-to-flux ratios range between ~2 and ~7, consistent with collapsing star-forming regions.

astro-ph.GA↗

arXiv2023

JOYS: Disentangling the warm and cold material in the high-mass IRAS 23385+6053 cluster

(abridged) We study and compare the warm (>100 K) and cold (<100 K) material toward the high-mass star-forming region IRAS 23385+6053 (IRAS 23385 hereafter) combining high angular resolution observations in the mid-infrared (MIR) with the JWST Observations of Young protoStars (JOYS) project and with the NOEMA at mm wavelengths at angular resolutions of 0.2"-1". The spatial morphology of atomic and molecular species is investigated by line integrated intensity maps. The temperature and column density of different gas components is estimated using H2 transitions (warm and hot component) and a series of CH3CN transitions as well as 3 mm continuum emission (cold component). Toward the central dense core in IRAS 23385 the material consists of relatively cold gas and dust (~50 K), while multiple outflows create heated and/or shocked H2 and show enhanced temperatures (~400 K) along the outflow structures. An energetic outflow with enhanced emission knots of [Fe II] and [Ni II] hints at J-type shocks, while two other outflows have enhanced emission of only H2 and [S I] caused by C-type shocks. The latter two outflows are also more prominent in molecular line emission at mm wavelengths (e.g., SiO, SO, H2CO, and CH3OH). Even higher angular resolution data are needed to unambiguously identify the outflow driving sources given the clustered nature of IRAS 23385. While most of the forbidden fine structure transitions are blueshifted, [Ne II] and [Ne III] peak at the source velocity toward the MIR source A/mmA2 suggesting that the emission is originating from closer to the protostar.

astro-ph.SR↗

arXiv2023

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE. II. A detailed kinematic analysis of the DR21 Main outflow

Molecular outflows are believed to be a key ingredient in the process of star formation. The molecular outflow associated with DR21 Main in Cygnus-X is one of the most extreme, in mass and size, molecular outflows in the Milky Way. The outflow is suggested to belong to a rare class of explosive outflows which are formed by the disintegration of protostellar systems.We aim to explore the morphology, kinematics,and energetics of the DR21 Main outflow, and compare those properties to confirmed explosive outflows to unravel the underlying driving mechanism behind DR21. Line and continuum emission are studied at a wavelength of 3.6\,mm with IRAM 30 m and NOEMA telescopes as part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program. The spectra include ($J= 1-0$) transitions of HCO$^+$, HCN, HNC, N$_2$H$^+$, H$_2$CO, CCH tracing different temperature and density regimes of the outflowing gas at high-velocity resolution ($\sim$ 0.8 km s$^{-1}$). The map encompasses the entire DR21 Main outflow and covers all spatial scales down to a resolution of ~3" ($\sim$ 0.02 pc). Integrated intensity maps of the HCO$^+$ emission reveal a strongly collimated bipolar outflow with significant overlap of the blue- and red-shifted emission. The opening angles of both outflow lobes decrease with velocity, from $\sim80$ to 20$^{\circ}$ for the velocity range from 5 to 45 km s$^{-1}$ relative to the source velocity. No evidence is found for the presence of elongated, "filament-like" structures expected in explosive outflows. N$_2$H$^+$ emission near the western outflow lobe reveals the presence of a dense molecular structure which appears to be interacting with the DR21 Main outflow. The overall morphology as well as the detailed kinematics of the DR21 Main outflow is more consistent with that of a typical bipolar outflow instead of an explosive counterpart.

astro-ph.GA↗