arXiv subjects

H. Beuther

Publications and source records attributed to H. Beuther.

At least 109 records · Page 6Linked to original sources

arXiv2020

Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster

We report the first map of large-scale (10 pc in length) emission of millimeter-wavelength hydrogen recombination lines (mm-RRLs) toward the giant H II region around the W43-Main young massive star cluster (YMC). Our mm-RRL data come from the IRAM 30 m telescope and are analyzed together with radio continuum and cm-RRL data from the Karl G. Jansky Very Large Array and HCO$^{+}$ 1-0 line emission data from the IRAM 30 m. The mm-RRLs reveal an expanding wind-blown ionized gas shell with an electron density ~70-1500 cm$^{-3}$ driven by the WR/OB cluster, which produces a total Ly$α$ photon flux of 1.5 x 10$^{50}$ s$^{-1}$. This shell is interacting with the dense neutral molecular gas in the W43-Main dense cloud. Combining the high spectral and angular resolution mm-RRL and cm-RRL cubes, we derive the two-dimensional relative distributions of dynamical and pressure broadening of the ionized gas emission and find that the RRL line shapes are dominated by pressure broadening (4-55 km s$^{-1}$) near the YMC and by dynamical broadening (8-36 km s$^{-1}$) near the shell's edge. Ionized gas clumps hosting ultra-compact H II regions found at the edge of the shell suggest that large-scale ionized gas motion triggers the formation of new star generation near the periphery of the shell.

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arXiv2020

Atomic and molecular gas properties during cloud formation

Molecular clouds, which harbor the birthplaces of stars, form out of the atomic phase of the interstellar medium (ISM). We aim to characterize the atomic and molecular phases of the ISM and set their physical properties into the context of cloud formation processes. We studied the cold neutral medium (CNM) by means of $\rm HI$ self-absorption (HISA) toward the giant molecular filament GMF20.0-17.9 and compared our results with molecular gas traced by $^{13}\rm CO$ emission. We fitted baselines of HISA features to $\rm HI$ emission spectra using first and second order polynomial functions. The CNM identified by this method spatially correlates with the morphology of the molecular gas toward the western region. However, no spatial correlation between HISA and $^{13}\rm CO$ is evident toward the eastern part of the filament. The distribution of HISA peak velocities and line widths agrees well with $^{13}\rm CO$ within the whole filament. The column density probability density functions (N-PDFs) of HISA (CNM) and $\rm HI$ emission (tracing both the CNM and the warm neutral medium, WNM) have a log-normal shape for all parts of the filament, indicative of turbulent motions as the main driver for these structures. The $\rm H_2$ N-PDFs show a broad log-normal distribution with a power-law tail suggesting the onset of gravitational contraction. The saturation of $\rm HI$ column density is observed at $\sim$25$\rm\,M_{\odot}\,pc^{-2}$. We conjecture that different evolutionary stages are evident within the filament. In the eastern region, we witness the onset of molecular cloud formation out of the atomic gas reservoir while the western part is more evolved, as it reveals pronounced $\rm H_2$ column density peaks and signs of active star formation.

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arXiv2020

Multi-wavelength modelling of the circumstellar environment of the massive proto-star AFGL 2591 VLA 3

We have studied the dust density, temperature and velocity distributions of the archetypal massive young stellar object (MYSO) AFGL 2591. Given its high luminosity ($L=2 \times 10^5$ L$_\odot$) and distance ($d=3.3$ kpc), AFGL 2591 has one of the highest $\sqrt{L}/d$ ratio, giving better resolved dust emission than any other MYSO. As such, this paper provides a template on how to use resolved multi-wavelength data and radiative transfer to obtain a well-constrained 2-D axi-symmetric analytic rotating infall model. We show for the first time that the resolved dust continuum emission from Herschel 70 $μ$m observations is extended along the outflow direction, whose origin is explained in part from warm dust in the outflow cavity walls. However, the model can only explain the kinematic features from CH$_3$CN observations with unrealistically low stellar masses ($<15$ M$_\odot$), indicating that additional physical processes may be playing a role in slowing down the envelope rotation. As part of our 3-step continuum and line fitting, we have identified model parameters that can be further constrained by specific observations. High-resolution mm visibilities were fitted to obtain the disc mass (6 M$_\odot$) and radius (2200 au). A combination of SED and near-IR observations were used to estimate the luminosity and envelope mass together with the outflow cavity inclination and opening angles.

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arXiv2020

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

The density structure of the interstellar medium (ISM) determines where stars form and release energy, momentum, and heavy elements, driving galaxy evolution. Density variations are seeded and amplified by gas motion, but the exact nature of this motion is unknown across spatial scale and galactic environment. Although dense star-forming gas likely emerges from a combination of instabilities, convergent flows, and turbulence, establishing the precise origin is challenging because it requires quantifying gas motion over many orders of magnitude in spatial scale. Here we measure the motion of molecular gas in the Milky Way and in nearby galaxy NGC 4321, assembling observations that span an unprecedented spatial dynamic range ($10^{-1}{-}10^3$ pc). We detect ubiquitous velocity fluctuations across all spatial scales and galactic environments. Statistical analysis of these fluctuations indicates how star-forming gas is assembled. We discover oscillatory gas flows with wavelengths ranging from $0.3{-}400$ pc. These flows are coupled to regularly-spaced density enhancements that likely form via gravitational instabilities. We also identify stochastic and scale-free velocity and density fluctuations, consistent with the structure generated in turbulent flows. Our results demonstrate that ISM structure cannot be considered in isolation. Instead, its formation and evolution is controlled by nested, interdependent flows of matter covering many orders of magnitude in spatial scale.

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arXiv2020

Dense Gas in a Giant Molecular Filament

Recent surveys of the Galactic plane in the dust continuum and CO emission lines reveal that large ($\gtrsim 50$~pc) and massive ($\gtrsim 10^5$~$M_\odot$) filaments, know as giant molecular filaments (GMFs), may be linked to galactic dynamics and trace the mid-plane of the gravitational potential in the Milky Way. We have imaged one entire GMF located at $l\sim$52--54$^\circ$ longitude, GMF54 ($\sim$68~pc long), in the empirical dense gas tracers using the HCN(1--0), HNC(1--0), HCO$^+$(1--0) lines, and their $^{13}$C isotopologue transitions, as well as the N$_2$H$^+$(1--0) line. We study the dense gas distribution, the column density probability density functions (N-PDFs) and the line ratios within the GMF. The dense gas molecular transitions follow the extended structure of the filament with area filling factors between 0.06 and 0.28 with respect to $^{13}$CO(1--0). We constructed the N-PDFs of H$_2$ for each of the dense gas tracers based on their column densities and assumed uniform abundance. The N-PDFs of the dense gas tracers appear curved in log-log representation, and the HCO$^+$ N-PDF has the largest log-normal width and flattest power-law slope index. Studying the N-PDFs for sub-regions of GMF54, we found an evolutionary trend in the N-PDFs that high-mass star forming and Photon-Dominate Regions (PDRs) have flatter power-law indices. The integrated intensity ratios of the molecular lines in GMF54 are comparable to those in nearby galaxies. In particular, the N$_2$H$^+$/$^{13}$CO ratio, which traces the dense gas fraction, has similar values in GMF54 and all nearby galaxies except ULIRGs.

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arXiv2020

Autonomous Gaussian decomposition of the Galactic Ring Survey. II. The Galactic distribution of 13CO

Knowledge about the distribution of CO emission in the Milky Way is essential to understand the impact of Galactic environment on the formation and evolution of structures in the interstellar medium. However, currently our insight about the fraction of CO in spiral arm and interarm regions is still limited by large uncertainties in assumed rotation curve models or distance determination techniques. In this work we use a Bayesian approach to obtain the current best assessment of the distribution of 13CO from the Galactic Ring Survey. We performed two different distance estimates that either included or excluded a model for Galactic features. We also include a prior for the solution of the kinematic distance ambiguity that was determined from a compilation of literature distances and an assumed size-linewidth relationship. We find that the fraction of 13CO emission associated with spiral arm features varies from 76% to 84% between the two distance runs. The vertical distribution of the gas is concentrated around the Galactic midplane showing FWHM values of ~75 pc. We do not find any significant difference between gas emission properties associated with spiral arm and interarm features. In particular the distribution of velocity dispersion values of gas emission in spurs and spiral arms is very similar. We detect a trend of higher velocity dispersion values with increasing heliocentric distance, which we attribute to beam averaging effects caused by differences in spatial resolution. We argue that the true distribution of the gas emission is likely more similar to a combination of our two distance results, and highlight the importance of using complementary distance estimations to safeguard against the pitfalls of any single approach. We conclude that the methodology presented in this work is a promising way to determine distances to gas emission features in Galactic plane surveys.

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arXiv2020

A Detailed View of the Circumstellar Environment and Disk of the Forming O-star AFGL 4176

We present a detailed analysis of the disk and circumstellar environment of the forming O-type star AFGL 4176 mm1, placing results from the Atacama Large Millimeter/submillimeter Array (ALMA) into context with multiwavelength data. With ALMA, we detect seventeen 1.2 mm continuum sources within 5$''$ (21,000 au) of AFGL 4176 mm1. We find that mm1 has a spectral index of 3.4$\pm$0.2 across the ALMA band, with $>$87% of its 1.2 mm continuum emission from dust. The source mm2, projected 4200 au from mm1, may be a companion or a blueshifted knot in a jet. We also explore the morphological differences between the molecular lines detected with ALMA, finding 203 lines from 25 molecules, which we categorize into several morphological types. Our results show that AFGL 4176 mm1 provides an example of a forming O-star with a large and chemically complex disk, which is mainly traced by nitrogen-bearing molecules. Lines that show strong emission on the blueshifted side of the disk are predominantly oxygen-bearing, which we suggest are tracing a disk accretion shock. The molecules C$^{34}$S, H$_2$CS and CH$_{3}$CCN trace a slow wide-angle wind or dense structures in the outflow cavity walls. With the Australia Telescope Compact Array (ATCA), we detect a compact continuum source ($<$2000 $\times$ 760 au) at 1.2 cm, associated with mm1, of which $>$96% is from ionized gas. The ATCA NH$_3$(1,1) and (2,2) emission traces a large-scale (r$\sim$0.5 pc) rotating toroid with the disk source mm1 in the blueshifted part of this structure offset to the northwest.

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arXiv2020

Complex organic molecules in low-mass protostars on solar system scales -- I. Oxygen-bearing species

Complex organic molecules (COMs) are thought to form on icy dust grains in the earliest phase of star formation. The evolution of these COMs from the youngest Class 0/I protostellar phases toward the more evolved Class II phase is still not fully understood. Since planet formation seems to start early, and mature disks are too cold for characteristic COM emission lines, studying the inventory of COMs on solar system scales in the Class 0/I stage is relevant. ALMA Band 3 (3 mm) and Band 6 (1 mm) observations are obtained of seven Class 0 protostars in the Perseus and Serpens star-forming regions. By modeling the inner protostellar region using 'LTE' models, the excitation temperature and column densities are determined for several O-bearing COMs. B1-c, B1-bS, and Serpens S68N show COM emission, i.e, three out of the seven sources. No clear correlation seems to exist between the occurrence of COMs and source luminosity. The abundances of several COMs with respect to CH3OH are remarkably similar for the three COM-rich sources, and to IRAS 16293-2422B and HH 212. For other COMs the abundances differ by up to an order of magnitude, indicating that local source conditions are case determining. B1-c hosts a cold ($T_{ex}\approx60$ K), more extended component of COM emission with a column density of typically a few % of the warm/hot ($T_{ex}\sim 200$ K), central component. A D/H ratio of 1-3 % is derived based on the CH2DOH/CH3OH ratio suggesting a temperature of $\sim$15~K during the formation of methanol. This ratio is consistent with other low-mass protostars. Future mid-infrared facilities such as JWST/MIRI will be essential to directly observe COM ices. Combining this with a larger sample of COM-rich sources with ALMA will allow for directly linking ice and gas-phase abundances in order to constrain the routes that produce and maintain chemical complexity during the star formation process.

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arXiv2020

Dynamical cloud formation traced by atomic and molecular gas

Context: Atomic and molecular cloud formation is a dynamical process. However, kinematic signatures of these processes are still observationally poorly constrained. Methods: Targeting the cloud-scale environment of the prototypical infrared dark cloud G28.3, we employ spectral line imaging observations of the two atomic lines HI and [CI] as well as molecular lines observations in 13CO in the 1--0 and 3--2 transitions. The analysis comprises investigations of the kinematic properties of the different tracers, estimates of the mass flow rates, velocity structure functions, a Histogram of Oriented Gradients (HOG) study as well as comparisons to simulations. Results: The central IRDC is embedded in a more diffuse envelope of cold neutral medium (CNM) traced by HI self-absorption (HISA) and molecular gas. The spectral line data as well as the HOG and structure function analysis indicate a possible kinematic decoupling of the HI from the other gas compounds. Spectral analysis and position-velocity diagrams reveal two velocity components that converge at the position of the IRDC. Estimated mass flow rates appear rather constant from the cloud edge toward the center. The velocity structure function analysis is consistent with gas flows being dominated by the formation of hierarchical structures. Conclusions: The observations and analysis are consistent with a picture where the IRDC G28 is formed at the center of two converging gas flows. While the approximately constant mass flow rates are consistent with a self-similar, gravitationally driven collapse of the cloud, external compression by, e.g., spiral arm shocks or supernovae explosions cannot be excluded yet. Future investigations should aim at differentiating the origin of such converging gas flows.

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arXiv2020

[CII] 158 μm self-absorption and optical depth effects

Context. The [CII] 158 μm 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

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arXiv2020

Spiral arms and instability within the AFGL 4176 mm1 disc

We present high-resolution (30 mas or 130 au at 4.2 kpc) Atacama Large Millimeter/submillimeter Array observations at 1.2 mm of the disc around the forming O-type star AFGL 4176 mm1. The disc (AFGL 4176 mm1-main) has a radius of ~1000 au and contains significant structure, most notably a spiral arm on its redshifted side. We fitted the observed spiral with logarithmic and Archimedean spiral models. We find that both models can describe its structure, but the Archimedean spiral with a varying pitch angle fits its morphology marginally better. As well as signatures of rotation across the disc, we observe gas arcs in CH$_3$CN that connect to other millimetre continuum sources in the field, supporting the picture of interactions within a small cluster around AFGL 4176 mm1-main. Using local thermodynamic equilibrium modelling of the CH$_3$CN K-ladder, we determine the temperature and velocity field across the disc, and thus produce a map of the Toomre stability parameter. Our results indicate that the outer disc is gravitationally unstable and has already fragmented or is likely to fragment in the future, possibly producing further companions. These observations provide evidence that disc fragmentation is one possible pathway towards explaining the high fraction of multiple systems around high-mass stars.

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arXiv2020

Characterization of unresolved and unclassified sources detected in radio continuum surveys of the Galactic plane

The continuum emission from 1 to 2 GHz of The HI/OH/Recombination line survey of the inner Milky Way (THOR) at $\lesssim$18" resolution covers $\sim 132$ square degrees of the Galactic plane and detects 10387 sources. Similarly, the first data release of the Global View of Star Formation in the Milky Way (GLOSTAR) surveys covers $\sim 16$ square degrees of the Galactic plane from 4-8 GHz at 18" resolution and detects 1575 sources. However, a large fraction of the unresolved discrete sources detected in these radio continuum surveys of the Galactic plane remain unclassified. Here, we study the Euclidean-normalized differential source counts of unclassified and unresolved sources detected in these surveys and compare them with simulated extragalactic radio source populations as well as previously established source counts. We find that the differential source counts for THOR and GLOSTAR surveys are in excellent agreement with both simulation and previous observations. We also estimate the angular two-point correlation function of unclassified and unresolved sources detected in THOR survey. We find a higher clustering amplitude in comparison with the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey up to the angular separation of $5^{\circ}$. The decrease in angular correlation with increasing flux cut and the excellent agreement of clustering pattern of sources above 1 mJy with high $z$ samples ($z >0.5$) of the FIRST survey indicates that these sources might be high $z$ extragalactic compact objects. The similar pattern of one-point and two-point statistics of unclassified and compact sources with extragalactic surveys and simulations confirms the extragalactic origin of these sources.

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arXiv2020

Cloud formation in the atomic and molecular phase: HI self absorption (HISA) towards a Giant Molecular Filament

Molecular clouds form from the atomic phase of the interstellar medium. However, characterizing the transition between the atomic and the molecular interstellar medium (ISM) is a difficult observational task. Here we address cloud formation processes by combining HSIA with molecular line data. One scenario proposed by numerical simulations is that the column density probability density functions (N-PDF) evolves from a log-normal shape at early times to a power-law-like shape at later times. In this paper, we study the cold atomic component of the giant molecular filament GMF38a (d=3.4 kpc, length$\sim230$ pc). We identify an extended HISA feature, which is partly correlated with the 13CO emission. The peak velocities of the HISA and 13CO observations agree well on the eastern side of the filament, whereas a velocity offset of approximately 4 km s$^{-1}$ is found on the western side. The sonic Mach number we derive from the linewidth measurements shows that a large fraction of the HISA, which is ascribed to the cold neutral medium (CNM), is at subsonic and transonic velocities. The column density of the CNM is on the order of 10$^{20}$ to 10$^{21}$ cm$^{-2}$. The column density of molecular hydrogen is an order of magnitude higher. The N-PDFs from HISA (CNM), HI emission (WNM+CNM), and 13CO (molecular component) are well described by log-normal functions, which is in agreement with turbulent motions being the main driver of cloud dynamics. The N-PDF of the molecular component also shows a power law in the high column-density region, indicating self-gravity. We suggest that we are witnessing two different evolutionary stages within the filament. The eastern subregion seems to be forming a molecular cloud out of the atomic gas, whereas the western subregion already shows high column density peaks, active star formation and evidence of related feedback processes.

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arXiv2019

The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and HI overview

With the $Karl~G.~Jansky$ Very Large Array (VLA) in C-configuration, we observed a large portion of the first Galactic quadrant ($l=14.0-67.4^\circ $ and $\lvert b \rvert \leq 1.25^\circ $) achieving an angular resolution of $\leq 40^{\prime\prime}$. At $L$ Band, the WIDAR correlator at the VLA was set to cover the 21~cm HI line, four OH transitions, a series of H$nα$ radio recombination lines (RRLs; $n=151$ to 186), and eight 128~MHz wide continuum spectral windows (SPWs) simultaneously. The HI emission shows clear filamentary substructures at negative velocities with low velocity crowding. The emission at positive velocities is more smeared-out likely due to higher spatial and velocity crowding of structures at the positive velocities. Comparing to the spiral arm model of the Milky Way, the atomic gas follows the Sagittarius and Perseus Arm well but with significant material in the inter-arm regions. With the C-configuration-only HI+continuum data, we produced a HI optical depth map of the THOR areal coverage from 228 absorption spectra with the nearest-neighbor method. With this $τ$ map, we corrected the HI emission for optical depth and the derived column density is 38% higher than the column density with optically thin assumption. The total HI mass with optical depth correction in the survey region is 4.7$\times10^8~M_\odot$, 31% more than the mass derived assuming the emission is optically thin. If we apply this 31% correction to the whole Milky Way, the total atomic gas mass would be 9.4-10.5$\times 10^9~M_\odot$. Comparing the HI with existing CO data, we find a significant increase in the atomic-to-molecular gas ratio from the spiral arms to the inter-arm regions.

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arXiv2019

The young stellar content of the giant HII regions M8, G333.6-0.2, and NGC6357 with VLT/KMOS

Context: The identification and characterisation of populations of young massive stars in (giant) HII regions provides important constraints on i) the formation process of massive stars and their early feedback on the environment, and ii) the initial conditions for population synthesis models predicting the evolution of ensembles of stars. Aims: We identify and characterise the stellar populations of the following young giant HII regions: M8, G333.6-0.2, and NGC6357. Methods: We acquired H- and K-band spectra of around 200 stars using The K-band KMOS on the ESO Very Large Telescope. The targets for M8 and NGC6357 were selected from the MYStIX project, which combines X-ray observations with near-infrared and mid-infrared data. For G333.6-0.2, the sample selection is based on the near-infrared colours combined with X-ray data. We introduce an automatic spectral classification method in order to obtain temperatures and luminosities for the observed stars. We analyse the stellar populations using their photometric, astrometric, and spectroscopic properties and compared the position of the stars in the Hertzprung-Russell diagram with stellar evolution models to constrain their ages and mass ranges. Results: We confirm the presence of candidate ionising sources in the three regions and report new ones, including the first spectroscopically identified O stars in G333.6-0.2. In M8 and NGC6357, two populations are identified: i) OB main-sequence stars ($M > 5~\rm{M_{\odot}}$) and ii) pre-main sequence stars ($M\approx0.5-5~\rm{M_{\odot}}$). The ages of the clusters are $\sim$1-3~Myr, $< 3$~Myr, and $\sim$0.5-3~Myr for M8, G333.6-0.2, and NGC6357, respectively. We show that MYStIX selected targets have $>$ 90\% probability of being members of the HII region, whereas a selection based on near infrared (NIR) colours leads to a membership probability of only $\sim$70\%.

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arXiv2019

Strong excess Faraday rotation on the Inside of the Sagittarius spiral arm

We present first results for Faraday rotation of compact polarized sources (1 to 2 GHz continuum) in The HI/OH/Recombination line (THOR) survey of the inner Galaxy. In the Galactic longitude range 39 degr < l < 52 degr, we find rotation measures in the range -310 rad/m2 < RM < +4219 rad/m2, with the highest values concentrated within a degree of l = 48 degrees at the Sagittarius arm tangent. Most of the high RMs arise in diffuse plasma, along lines of sight that do not intersect HII regions. For l > 49 degr, RM drops off rapidly, while at l < 47 degr, the mean RM is higher with a larger standard deviation than at l > 49 degr. We attribute the RM structure to the compressed diffuse Warm Ionized Medium in the spiral arm, upstream of the major star formation regions. The Sagittarius arm acts as a significant Faraday screen inside the Galaxy. This has implications for models of the Galactic magnetic field and the expected amount of Faraday rotation of Fast Radio Bursts from their host galaxies. We emphasize the importance of sensitivity to high Faraday depth in future polarization surveys.

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arXiv2019

Autonomous Gaussian decomposition of the Galactic Ring Survey. I. Global statistics and properties of the 13CO emission data

The analysis of large molecular line surveys of the Galactic plane is essential for our understanding of the gas kinematics on Galactic scales, in particular its link with the formation and evolution of dense structures in the interstellar medium. An approximation of the emission peaks with Gaussian functions allows for an efficient and straightforward extraction of useful physical information contained in the shape and Doppler-shifted frequency of the emission lines contained in these enormous data sets. In this work we present an overview and first results of a Gaussian decomposition of the entire Galactic Ring Survey (GRS) 13CO (1-0) data that consists of about 2.3 million spectra. We performed the decomposition with the fully automated GaussPy+ algorithm and fitted about 4.6 million Gaussian components to the GRS spectra. We discuss the statistics of the fit components and relations between the fitted intensities, velocity centroids, and velocity dispersions. We find that the magnitude of the velocity dispersion values increase toward the inner Galaxy and around the Galactic midplane, which we speculate is partly due to the influence of the Galactic bar and regions with higher non-thermal motions located in the midplane, respectively. We also use our decomposition results to infer global properties of the gas emission and find that the number of fit components used per spectrum is indicative for the amount of structure along the line of sight. We find that the emission lines from regions located on the far side of the Galaxy show increased velocity dispersion values, likely due to beam averaging effects. We demonstrate how this trend has the potential to aid in characterising Galactic structure by disentangling emission that is belonging to the nearby Aquila Rift molecular cloud from emission that is more likely associated with the Perseus and Outer spiral arms.

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arXiv2019

Chemical complexity in high-mass star formation: An observational and modeling case study of the AFGL 2591 VLA 3 hot core

We present a detailed observational and modeling study of the hot core VLA 3 in the high-mass star-forming region AFGL 2591, which is a target region of the NOrthern Extended Millimeter Array (NOEMA) large program CORE. Using NOEMA observations at 1.37 mm with an angular resolution of ~0."42 (1 400 au at 3.33 kpc), we derived the physical and chemical structure of the source. We modeled the observed molecular abundances with the chemical evolution code MUSCLE (MUlti Stage ChemicaL codE). Results. With the kinetic temperature tracers CH3CN and H2CO we observe a temperature distribution with a power-law index of q = 0.41+-0.08. Using the visibilities of the continuum emission we derive a density structure with a power-law index of p = 1.7+-0.1. The hot core spectra reveal high molecular abundances and a rich diversity in complex molecules. The majority of the molecules have an asymmetric spatial distribution around the forming protostar(s), which indicates a complex physical structure on scales < 1 400 au. Using MUSCLE, we are able to explain the observed molecular abundance of 10 out of 14 modeled species at an estimated hot core chemical age of ~21 100 years. In contrast to the observational analysis, our chemical modeling predicts a lower density power-law index of p < 1.4. Reasons for this discrepancy are discussed. Conclusions. Combining high spatial resolution observations with detailed chemical modeling allows us to derive a concise picture of the physical and chemical structure of the famous AFGL 2591 hot core. The next steps are to conduct a similar analysis for the whole CORE sample, and then use this analysis to constrain the chemical diversity in high-mass star formation to a much greater depth.

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