arXiv subjects

F. Wyrowski

Publications and source records attributed to F. Wyrowski.

At least 91 records · Page 5Linked to original sources

arXiv2021

Observations of multiple NH$_3$ transitions in W33

At a distance of 2.4kpc, W33 is an outstanding massive and luminous 10pc sized star forming complex containing quiescent infrared dark clouds as well as highly active infrared bright cloud cores heated by young massive stars. We report measurements of ammonia (NH$_3$) inversion lines in the frequency range 18--26GHz, obtained with the 40" resolution of the 100 m Effelsberg telescope. We have detected the ($J$, $K$)=(1,1), (2,2), (3,3), (4,4), (5,5), (6,6), (2,1) and (3,2) transitions. There is a maser line in the (3,3) transition towards W33 Main. Brightness temperature and line shape indicate no significant variation during the last $\sim$36yr. We have determined kinetic temperatures, column densities and other physical properties of NH$_3$ and the molecular clouds in W33. For the total-NH$_3$ column density, we find for 40"(0.5pc) sized regions 6.0($\pm$2.1)$\times$10$^{14}$, 3.5($\pm$0.1)$\times$10$^{15}$, 3.4($\pm$0.2)$\times$10$^{15}$, 3.1($\pm$0.2)$\times$10$^{15}$, 2.8($\pm$0.2)$\times$10$^{15}$ and 2.0($\pm$0.2)$\times$10$^{15}$cm$^{-2}$ at the peak positions of W33 Main, W33 A, W33 B, W33 Main1, W33 A1 and W33 B1, respectively. W33 Main has a total-NH$_3$ fractional abundance of 1.3($\pm$0.1)$\times$10$^{-9}$ at the peak position. High values of 1.4($\pm$0.3)$\times$10$^{-8}$, 1.6($\pm$0.3)$\times$10$^{-8}$, 3.4($\pm$0.5)$\times$10$^{-8}$, 1.6($\pm$0.5)$\times$10$^{-8}$ and 4.0($\pm$1.2)$\times$10$^{-8}$ are obtained at the central positions of W33 A, W33 B, W33 Main1, W33 A1, and W33 B1. From this, we confirm the already previously proposed different evolutionary stages of the six W33 clumps and find that there is no hot core in the region approaching the extreme conditions encountered in W51-IRS2 or Sgr B2. The ortho-to-para-NH$_3$ abundance ratios suggest that ammonia should have been formed in the gas phase or on dust grain mantles at kinetic temperatures of $\gtrsim$20K.

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arXiv2021

OGHReS: Large-scale filaments in the outer Galaxy

Filaments are a ubiquitous morphological feature of the molecular interstellar medium and are identified as sites of star formation. In recent years, more than 100 large-scale filaments (with a length $>10$\,pc) have been observed in the inner Milky Way. As they appear linked to Galactic dynamics, studying those structures represents an opportunity to link kiloparsec-scale phenomena to the physics of star formation, which operates on much smaller scales. In this letter, we use newly acquired Outer Galaxy High Resolution Survey (OGHReS) $^{12}$CO(2-1) data to demonstrate that a significant number of large-scale filaments are present in the outer Galaxy as well. The 37 filaments identified appear tightly associated with inter-arm regions. In addition, their masses and linear masses are, on average, one order of magnitude lower than similar-sized molecular filaments located in the inner Galaxy, showing that Milky Way dynamics is able to create very elongated features in spite of the lower gas supply in the Galactic outskirts.

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arXiv2021

Establishing the evolutionary timescales of the massive star formation process through chemistry

(Abridged) Understanding the details of the formation process of massive (i.e. M<8-10M$_\odot$) stars is a long-standing problem in astrophysics. [...] We present a method to derive accurate timescales of the different evolutionary phases of the high-mass star formation process. We model a representative number of massive clumps of the ATLASGAL-TOP100 sample which cover all the evolutionary stages. The models describe an isothermal collapse and the subsequent warm-up phase, for which we follow their chemical evolution. The timescale of each phase is derived by comparing the results of the models with the properties of the sources of the ATLASGAL-TOP100 sample, taking into account the mass and luminosity of the clumps, and the column densities of methyl acetylene (CH$_3$CCH), acetonitrile (CH$_3$CN), formaldehyde (H$_2$CO) and methanol (CH$_3$OH). We find that the chosen molecular tracers are affected by the thermal evolution of the clumps, showing steep ice evaporation gradients from 10$^3$ to 10$^5$ AU during the warm-up phase. We succeed in reproducing the observed column densities of CH$_3$CCH and CH$_3$CN, while H$_2$CO and CH$_3$OH show a poorer agreement with the observed values. The total (massive) star formation time is found to be $\sim5.2\times10^5$ yr, which is defined by the timescales of the individual evolutionary phases of the ATLASGAL-TOP100 sample: $\sim5\times10^4$ yr for 70-$μ$m weak, $\sim1.2\times10^5$ yr for mid-IR weak, $\sim2.4\times10^5$ yr for mid-IR bright and $\sim1.1\times10^5$ yr for HII-regions phases. Our models, with an appropriate selection of molecular tracers that can act as chemical clocks, allow to get robust estimates of the duration of the individual phases of the high-mass star formation process, with the advantage of being capable to include additional tracers aimed at increasing the accuracy of the estimated timescales.

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arXiv2021

The SEDIGISM survey: The influence of spiral arms on the molecular gas distribution of the inner Milky Way

The morphology of the Milky Way is still a matter of debate. In order to shed light on uncertainties surrounding the structure of the Galaxy, in this paper, we study the imprint of spiral arms on the distribution and properties of its molecular gas. To do so, we take full advantage of the SEDIGISM survey that observed a large area of the inner Galaxy in the $^{13}$CO(2-1) line at an angular resolution of 28". We analyse the influences of the spiral arms by considering the features of the molecular gas emission as a whole across the longitude-velocity map built from the full survey. Additionally, we examine the properties of the molecular clouds in the spiral arms compared to the properties of their counterparts in the inter-arm regions. Through flux and luminosity probability distribution functions, we find that the molecular gas emission associated with the spiral arms does not differ significantly from the emission between the arms. On average, spiral arms show masses per unit length of $\sim10^5-10^6$ M$_{\odot} $kpc$^{-1}$. This is similar to values inferred from data sets in which emission distributions were segmented into molecular clouds. By examining the cloud distribution across the Galactic plane, we infer that the molecular mass in the spiral arms is a factor of 1.5 higher than that of the inter-arm medium, similar to what is found for other spiral galaxies in the local Universe. We observe that only the distributions of cloud mass surface densities and aspect ratio in the spiral arms show significant differences compared to those of the inter-arm medium; other observed differences appear instead to be driven by a distance bias. By comparing our results with simulations and observations of nearby galaxies, we conclude that the measured quantities would classify the Milky Way as a flocculent spiral galaxy, rather than as a grand-design one.

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arXiv2021

High resolution LAsMA $^{12}$CO and $^{13}$CO observation of the G305 giant molecular cloud complex : II. Effect of feedback on clump properties

G305 star-forming complex was observed in the 3-2 lines of 12 & 13CO to investigate the effect of feedback from the central OB stars on the complex. The region was decomposed into clumps using dendrogram analysis. A catalog of the clump properties was created. The surface mass densities of the clumps were plotted as a function of the incident 8um flux. A mask of the region with 8um flux >100 MJy/sr was created and clumps were categorized based on the extent of overlap with the mask into "mostly inside" , "partly inside'", & "outside". The surface mass density distribution of each of these populations were plotted. This was followed by comparing the G305 clumps with the Galactic average taken from the ATLASGAL and CHIMPS clumps. Finally, the cumulative distribution functions (CDF) of the clump masses in G305 and their L/M ratios were compared to that of the Galactic sample. The surface mass densities of clumps showed a positive correlation with the incident 8um flux. The data did not have sufficient velocity resolution to discern the effects of feedback on the linewidths of the clumps. The sub-sample of clumps named "mostly inside" had the highest surface mass densities followed by "partly inside" and "outside" sub-samples. These differences between the three sub-samples were shown to be statistically significant using the KS test. The "mostly inside" sample also showed the highest level of fragmentation compared to the other two. These prove that the clumps inside the G305 region are triggered. The G305 clump population is also statistically different from the Galactic average population rejecting redistribution as a likely consequence of feedback. The CDFs of clump masses and their L/M ratios are both flatter than the Galactic average, indicating that feedback in G305 has triggered star formation. The collect and collapse method is the dominant mechanism at play in G305.

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arXiv2021

Disk fragmentation in high-mass star formation. High-resolution observations towards AFGL 2591-VLA 3

Increasing evidence suggests that, similar to their low-mass counterparts, high-mass stars form through a disk-mediated accretion process. At the same time, formation of high-mass stars still necessitates high accretion rates, and hence, high gas densities, which in turn can cause disks to become unstable against gravitational fragmentation. We study the kinematics and fragmentation of the disk around the high-mass star forming region AFGL 2591-VLA 3 which was hypothesized to be fragmenting based on the observations that show multiple outflow directions. We use a new set of high-resolution (0.19 arcsec) IRAM/NOEMA observations at 843 micron towards VLA 3 which allow us to resolve its disk, characterize the fragmentation, and study its kinematics. In addition to the 843 micron continuum emission, our spectral setup targets warm dense gas and outflow tracers such as HCN, HC$_3$N and SO$_2$, as well as vibrationally excited HCN lines. The high resolution continuum and line emission maps reveal multiple fragments with subsolar masses within the inner 1000 AU of VLA 3. Furthermore, the velocity field of the inner disk observed at 843 micron shows a similar behavior to that of the larger scale velocity field studied in the CORE project at 1.37 mm. We present the first observational evidence for disk fragmentation towards AFGL 2591-VLA 3, a source that was thought to be a single high-mass core. While the fragments themselves are low-mass, the rotation of the disk is dominated by the protostar with a mass of 10.3$\pm 1.8~M_{\odot}$. These data also show that NOEMA Band 4 can obtain the highest currently achievable spatial resolution at (sub-)mm wavelengths in observations of strong northern sources.

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arXiv2021

The ionization fraction in OMC-2 and OMC-3

The electron density ($n_{e^{-}}$) plays an important role in setting the chemistry and physics of the interstellar medium. However, measurements of $n_{e^{-}}$ in neutral clouds have been directly obtained only toward a few lines of sight or they rely on indirect determinations. We use carbon radio recombination lines and the far-infrared lines of C$^{+}$ to directly measure $n_{e^{-}}$ and the gas temperature in the envelope of the integral shaped filament (ISF) in the Orion A molecular cloud. We observed the C$102α$ and C$109α$ carbon radio recombination lines (CRRLs) using the Effelsberg 100m telescope at ~2' resolution toward five positions in OMC-2 and OMC-3. Since the CRRLs have similar line properties, we averaged them to increase the signal-to-noise ratio of the spectra. We compared the intensities of the averaged CRRLs, and the 158 μm-[CII] and [$^{13}$CII] lines to the predictions of a homogeneous model for the C$^{+}$/C interface in the envelope of a molecular cloud and from this comparison we determined the electron density, temperature and C$^{+}$ column density of the gas. We detect the CRRLs toward four positions, where their velocity and widths (FWHM 2.3 km s$^{-1}$) confirms that they trace the envelope of the ISF. Toward two positions we detect the CRRLs, and the [CII] and [$^{13}$CII] lines with a signal-to-noise ratio >5, and we find $n_{e^{-}}=0.65\pm0.12$ cm$^{-3}$ and $0.95\pm0.02$ cm$^{-3}$, which corresponds to a gas density $n_{H}\approx5\times10^{3}$ cm$^{-3}$ and a thermal pressure of $p_{th}\approx4\times10^{5}$ K cm$^{-3}$. We also constrained the ionization fraction in the denser portions of the molecular cloud using the HCN(1-0) and C$_{2}$H(1-0) lines to $x(e^{-})<3\times10^{-6}$. The derived electron densities and ionization fraction imply that $x(e^{-})$ drops by a factor >100 between the C$^{+}$ layer and the regions probed by HCN(1-0).

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arXiv2021

A global view on star formation: The GLOSTAR Galactic plane survey. II. Supernova Remnants in the first quadrant of the Milky Way

Context. The properties of the population of Galactic supernova remnants (SNRs) are essential to our understanding of the dynamics of the interstellar medium (ISM) in the Milky Way. However, the completeness of the catalog of Galactic SNRs is expected to be only ${\sim}30\%$, with on order 700 SNRs yet to be detected. Deep interferometric radio continuum surveys of the Galactic plane help in rectifying this apparent deficiency by identifying low surface brightness SNRs and compact SNRs that have not been detected in previous surveys. However, SNRs are routinely confused with H II regions, which can have similar radio morphologies. Radio spectral index, polarization, and emission at mid-infrared (MIR) wavelengths can help distinguish between SNRs and H II regions. Aims. We aim to identify SNR candidates using continuum images from the Karl G. Jansky Very Large Array GLObal view of the STAR formation in the Milky Way (GLOSTAR) survey. Methods. GLOSTAR is a C-band (4--8 GHz) radio wavelength survey of the Galactic plane covering $358^{\circ} \leq l \leq 60^{\circ}, |b| \leq 1^{\circ}$. The continuum images from this survey, which resulted from observations with the most compact configuration of the array, have an angular resolution of $18''$. We searched for SNRs in these images to identify known SNRs, previously identified SNR candidates, and new SNR candidates. We study these objects in MIR surveys and the GLOSTAR polarization data to classify their emission as thermal or nonthermal. Results. We identify 157 SNR candidates, of which 80 are new. Polarization measurements provide evidence of nonthermal emission from 9 of these candidates. We find that two previously identified candidates are filaments. We also detect emission from 91 of the 94 known SNRs in the survey region. Four of these are reclassified as H II regions following detection in MIR surveys. (Abridged)

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arXiv2021

A global view on star formation: The GLOSTAR Galactic Plane Survey. I. Overview and first results for the Galactic longitude range 28° < l < 36°

Surveys of the Milky Way at various wavelengths have changed our view of star formation in our Galaxy considerably in recent years. In this paper we give an overview of the GLOSTAR survey, a new survey covering large parts (145 square degrees) of the northern Galactic plane using the Karl G. Jansky Very Large Array (JVLA) in the frequency range 4-8 GHz and the Effelsberg 100-m telescope. This provides for the first time a radio survey covering all angular scales down to 1.5 arcsecond, similar to complementary near-IR and mid-IR galactic plane surveys. We outline the main goals of the survey and give a detailed description of the observations and the data reduction strategy. In our observations we covered the radio continuum in full polarization, as well as the 6.7 GHz methanol maser line, the 4.8~GHz formaldehyde line, and seven radio recombination lines. The observations were conducted in the most compact D configuration of the VLA and in the more extended B configuration. This yielded spatial resolutions of 18" and 1.5" for the two configurations, respectively. We also combined the D configuration images with the Effelsberg 100-m data to provide zero spacing information, and we jointly imaged the D- and B-configuration data for optimal sensitivity of the intermediate spatial ranges. Here we show selected results for the first part of the survey, covering the range of 28 deg <l<36 deg and |b|< 1 deg, including the full low-resolution continuum image, examples of high-resolution images of selected sources, and the first results from the spectral line data.

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arXiv2021

High Resolution LAsMA $^{12}$CO and $^{13}$CO Observation of the G305 Giant Molecular Cloud Complex : I. Feedback on the Molecular Gas

We observed the G305 star forming complex in the $J=3\text{-}2$ lines of $^{12}$CO and $^{13}$CO to investigate how molecular gas surrounding the central stellar clusters is being impacted by feedback. The APEX telescope's LAsMA multi-beam receiver was used to observe the region. Excitation temperatures and column density maps were produced. Combining our data with data from the SEDIGISM survey resulted in a $^{13}$CO $J=3\text{-}2/2\text{-}1$ excitation map. To verify whether feedback from stellar clusters is responsible for exciting the gas, the distribution of CO excitation was compared with that of 8$\,μ\rm{m}$ emission imaged with Spitzer, which is dominated by UV-excited emission from PAHs. Line centroid velocities, as well as stacked line profiles were examined to investigate the effect of feedback on the gas dynamics. Line profiles along radially outward directions demonstrate that the excitation temperature and $^{13}$CO $J=3\text{-}2/2\text{-}1$ ratio increase steeply by factors of $\sim\,2-3$ at the edge of the denser gas traced by $^{13}$CO that faces the hot stars at the center of the complex and steadily decreases away from it. Column density also increases at the leading edge, but does not always decrease steadily outward. Regions with higher 8$\,μ\rm{m}$ flux have higher median excitation temperatures, column densities and $^{13}$CO $J=3\text{-}2/2\text{-}1$ ratio. The centroid velocity probability distribution function of the region shows exponential wings, indicative of turbulence driven by strong stellar winds. Stacked spectra in regions with stronger feedback have higher skewness and narrower peaks with pronounced wings compared to regions with weaker feedback. Feedback from the stellar cluster in G305 has demonstrable effects on the excitation as well as on the dynamics of the giant molecular cloud.

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arXiv2021

A global view on star formation: The GLOSTAR Galactic plane survey IV. Radio continuum detections of young stellar objects in the Galactic Centre region

The Central Molecular Zone (CMZ), a $\sim$200 pc sized region around the Galactic Centre, is peculiar in that it shows a star formation rate (SFR) that is suppressed with respect to the available dense gas. To study the SFR in the CMZ, young stellar objects (YSOs) can be investigated. Here we present radio observations of 334 2.2 $μ$m infrared sources that have been identified as YSO candidates. Our goal is to investigate the presence of centimetre wavelength radio continuum counterparts to this sample of YSO candidates which we use to constrain the current SFR in the CMZ. As part of the GLOSTAR survey, D-configuration VLA data was obtained for the Galactic Centre, covering -2$^{\circ}<l<$2$^{\circ}$ and -1$^{\circ}<b<$1$^{\circ}$, with a frequency coverage of 4-8 GHz. We matched YSOs with radio continuum sources based on selection criteria and classified these radio sources as potential HII regions and determined their physical properties. Of the 334 YSO candidates, we found 35 with radio continuum counterparts. We find that 94 YSOs are associated with dense dust condensations identified in the 870 $μ$m ATLASGAL survey, of which 14 have a GLOSTAR counterpart. Of the 35 YSOs with radio counterparts, 11 are confirmed as HII regions, based on their spectral indices and the literature. We estimated their Lyman continuum photon flux in order to estimate the mass of the ionising star. Combining these with known sources, the present-day SFR in the CMZ is calculated to be $\sim$0.068 M$_{\odot}$ yr$^{-1}$, which is $\sim$6.8$\%$ of the Galactic SFR. Candidate YSOs that lack radio counterparts may not have yet evolved to the stage of exhibiting an HII region or, conversely, are older and have dispersed their natal clouds. Since many lack dust emission, the latter is more likely. Our SFR estimate in the CMZ is in agreement with previous estimates in the literature.

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arXiv2021

Identification of prestellar cores in high-mass star forming clumps via $\rm H_2D^+$ observations with ALMA

Context. The different theoretical models concerning the formation of high-mass stars make distinct predictions regarding their progenitors, i.e. the high-mass prestellar cores. However, so far no conclusive observation of such objects has been made. Aims. We aim to study the very early stages of high-mass star formation in two infrared-dark, massive clumps, to identify the core population that they harbour. Methods. We obtained ALMA observations of continuum emission at 0.8mm and of the ortho-$\rm H_2D^+$ transition at 372GHz towards the two clumps. We use the SCIMES algorithm to identify cores in the position-position-velocity space, finding 16 cores. We model their observed spectra in the LTE approximation, deriving the centroid velocity, linewidth, and column density maps. We also study the correlation between the continuum and molecular data, which in general do not present the same structure. Results. We report for the first time the detection of ortho-$\rm H_2D^+$ in high-mass star-forming regions performed with an interferometer. The molecular emission shows narrow and subsonic lines, suggesting that locally the temperature of the gas is less than 10K. From the continuum emission we estimate the cores' total masses, and compare them with the respective virial masses. We also compute the volume density values, which are found to be higher than $10^{6}\, \rm cm^{-3}$. Conclusions. Our data confirm that ortho-$\rm H_2D^+$ is an ideal tracer of cold and dense gas. Interestingly, almost all the $\rm H_2D^+$-identified cores are less massive than 13M_sun , with the exception of one core in AG354. Furthermore, most of them are subvirial and larger than their Jeans masses. These results are difficult to explain in the context of the turbulent accretion models, which predict massive and virialised prestellar cores.

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arXiv2021

Fragmentation and kinematics in high-mass star formation: CORE-extension targeting two very young high-mass star-forming regions

Context: The formation of high-mass star-forming regions from their parental gas cloud and the subsequent fragmentation processes lie at the heart of star formation research. Aims: We aim to study the dynamical and fragmentation properties at very early evolutionary stages of high-mass star formation. Methods: Employing the NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30m telescope, we observed two young high-mass star-forming regions, ISOSS22478 and ISOSS23053, in the 1.3mm continuum and spectral line emission at a high angular resolution (~0.8''). Results: We resolved 29 cores that are mostly located along filament-like structures. Depending on the temperature assumption, these cores follow a mass-size relation of approximately M~r^2.0, corresponding to constant mean column densities. However, with different temperature assumptions, a steeper mass-size relation up to M~r^3.0, which would be more likely to correspond to constant mean volume densities, cannot be ruled out. The correlation of the core masses with their nearest neighbor separations is consistent with thermal Jeans fragmentation. We found hardly any core separations at the spatial resolution limit, indicating that the data resolve the large-scale fragmentation well. Although the kinematics of the two regions appear very different at first sight - multiple velocity components along filaments in ISOSS22478 versus a steep velocity gradient of more than 50km/s/pc in ISOSS23053 - the findings can be explained within the framework of a dynamical cloud collapse scenario. Conclusions: While our data are consistent with a dynamical cloud collapse scenario and subsequent thermal Jeans fragmentation, the importance of additional environmental properties, such as the magnetization of the gas or external shocks triggering converging gas flows, is nonetheless not as well constrained and would require future investigation.

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arXiv2021

The physical and chemical structure of high-mass star-forming regions. Unraveling chemical complexity with the NOEMA large program "CORE"

We use sub-arcsecond resolution ($\sim$0.4$''$) observations with NOEMA at 1.37 mm to study the dust emission and molecular gas of 18 high-mass star-forming regions. We combine the derived physical and chemical properties of individual cores in these regions to estimate their ages. The temperature structure of these regions are determined by fitting H2CO and CH3CN line emission. The density profiles are inferred from the 1.37 mm continuum visibilities. The column densities of 11 different species are determined by fitting the emission lines with XCLASS. Within the 18 observed regions, we identify 22 individual cores with associated 1.37 mm continuum emission and with a radially decreasing temperature profile. We find an average temperature power-law index of q = 0.4$\pm$0.1 and an average density power-law index of p = 2.0$\pm$0.2 on scales on the order of several 1 000 au. Comparing these results with values of p derived in the literature suggest that the density profiles remain unchanged from clump to core scales. The column densities relative to N(C18O) between pairs of dense gas tracers show tight correlations. We apply the physical-chemical model MUSCLE to the derived column densities of each core and find a mean chemical age of $\sim$60 000 yrs and an age spread of 20 000-100 000 yrs. With this paper we release all data products of the CORE project available at https://www.mpia.de/core. The CORE sample reveals well constrained density and temperature power-law distributions. Furthermore, we characterize a large variety in molecular richness that can be explained by an age spread confirmed by our physical-chemical modeling. The hot molecular cores show the most emission lines, but we also find evolved cores at an evolutionary stage, in which most molecules are destroyed and thus the spectra appear line-poor again.

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arXiv2021

The distribution of ionized, atomic and PDR gas around S1 in Rho Ophiuchus

The early B star S1 in the Rho Ophiuchus cloud excites an HII region and illuminates a large egg-shaped photodissociation (PDR) cavity. The PDR is restricted to the west and south-west by the dense molecular Rho Oph A ridge, expanding more freely into the diffuse low density cloud to the north-east. We analyze new SOFIA GREAT, GMRT and APEX data together with archival data from Herschel/PACS, JCMT/HARPS to study the properties of the photo-irradiated ionized and neutral gas in this region. The tracers include [C II] at 158 micron, [O I] at 63 and 145 micron, J=6-5 transitions of CO and 13CO, HCO+ (4-3), radio continuum at 610 and 1420 MHz and HI at 21 cm. The PDR emission is strongly red-shifted to the south-east of the nebula, and primarily blue-shifted on the north western side. The [C II] and and [O I]63 spectra are strongly self-absorbed over most of the PDR. By using the optically thin counterparts, [13C II] and [O I]145 respectively, we conclude that the self-absorption is dominated by the warm (>80 K) foreground PDR gas and not by the surrounding cold molecular cloud. We estimate the column densities of C+ and O of the PDR to be 3e18 and 2e19 cm^-2, respectively. Comparison of stellar far-ultraviolet flux and reprocessed infrared radiation suggest enhanced clumpiness of the gas to the north-west. Analysis of the emission from the PDR gas suggests the presence of at least three density components consisting of high density (10^6 cm^-3) clumps, medium density (10^4 cm^-3) and diffuse (10^3 cm^-3) interclump medium. The medium density component primarily contributes to the thermal pressure of the PDR gas which is in pressure equilibrium with the molecular cloud to the west. We find that the PDR is tilted and warped with the south-eastern side of the cavity being denser on the front and the north-western side being denser on the rear.

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arXiv2021

ATLASGAL -- selected massive clumps in the inner Galaxy. IX. Deuteration of ammonia

Deuteration has been used as a tracer of the evolutionary phases of low- and high-mass star formation. The APEX Telescope Large Area Survey (ATLASGAL) provides an important repository for a detailed statistical study of massive star-forming clumps in the inner Galactic disc at different evolutionary phases. We study the amount of deuteration using NH2D in a representative sample of high-mass clumps discovered by the ATLASGAL survey covering various evolutionary phases of massive star formation. Unbiased spectral line surveys at 3 mm were thus conducted towards ATLASGAL clumps between 85 and 93 GHz with the Mopra telescope and from 84 to 115 GHz using the IRAM 30m telescope. A subsample was followed up in the NH2D transition at 74 GHz with the IRAM 30m telescope. We determined the deuterium fractionation from the column density ratio of NH2D and NH3 and measured the NH2D excitation temperature for the first time from the simultaneous modelling of the 74 and 110 GHz line using MCWeeds. We find a large range of the NH2D to NH3 column density ratio up to 1.6+/-0.7 indicating a high degree of NH3 deuteration in a subsample of the clumps. Our analysis yields a clear difference between NH3 and NH2D rotational temperatures for a fraction of the sources. We therefore advocate observation of the NH2D transitions at 74 and 110 GHz simultaneously to determine the NH2D temperature directly. We determine a median ortho-to-para column density ratio of 3.7+/-1.2. The high detection rate of NH2D confirms a high deuteration previously found in massive star-forming clumps. Using the excitation temperature of NH2D instead of NH3 is needed to avoid an overestimation of deuteration. We measure a higher detection rate of NH2D in sources at early evolutionary stages. The deuterium fractionation shows no correlation with evolutionary tracers such as the NH3 (1,1) line width, or rotational temperature.

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arXiv2021

Physical and chemical structure of the Serpens filament -- fast formation and gravity-driven accretion

The Serpens filament, a prominent elongated structure in a relatively nearby molecular cloud, is believed to be at an early evolutionary stage, so studying its physical and chemical properties can shed light on filament formation and early evolution. The main goal is to address the physical and chemical properties as well as the dynamical state of the Serpens filament at a spatial resolution of $\sim$0.07 pc and a spectral resolution of $\lesssim$0.1~km~s$^{-1}$. We performed $^{13}$CO (1--0), C$^{18}$O (1--0), C$^{17}$O (1--0), $^{13}$CO (2--1), C$^{18}$O (2--1), and C$^{17}$O (2--1) imaging observations toward the Serpens filament with the Institut de Radioastronomie Millim{é}trique 30-m (IRAM-30 m) and Atacama Pathfinder EXperiment (APEX) telescopes. Widespread narrow $^{13}$CO (2--1) self-absorption is observed in this filament, causing the $^{13}$CO morphology to be different from the filamentary structure traced by C$^{18}$O and C$^{17}$O. Our excitation analysis suggests that the opacities of C$^{18}$O transitions become higher than unity in most regions, and this analysis confirms the presence of widespread CO depletion. Further we show that the local velocity gradients have a tendency to be perpendicular to the filament's long axis in the outskirts and parallel to the large-scale magnetic field direction. The magnitudes of the local velocity gradients decrease toward the filament's crest. The observed velocity structure can be a result of gravity-driven accretion flows. The isochronic evolutionary track of the C$^{18}$O freeze-out process indicates the filament is young with an age of $\lesssim$2 Myr. We propose that the Serpens filament is a newly-formed slightly-supercritical structure which appears to be actively accreting material from its ambient gas.

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arXiv2020

The SEDIGISM survey: first data release and overview of the Galactic structure

The SEDIGISM (Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium) survey used the APEX telescope to map 84 deg^2 of the Galactic plane between l = -60 deg and l = +31 deg in several molecular transitions, including 13CO(2-1) and C18O(2-1), thus probing the moderately dense (~10^3 cm^-3) component of the interstellar medium. With an angular resolution of 30'' and a typical 1-sigma sensitivity of 0.8-1.0 K at 0.25 km/s velocity resolution, it gives access to a wide range of structures, from individual star-forming clumps to giant molecular clouds and complexes. The coverage includes a good fraction of the first and fourth Galactic quadrants, allowing us to constrain the large scale distribution of cold molecular gas in the inner Galaxy. In this paper we provide an updated overview of the full survey and the data reduction procedures used. We also assess the quality of these data and describe the data products that are being made publicly available as part of this first data release (DR1). We present integrated maps and position-velocity maps of the molecular gas and use these to investigate the correlation between the molecular gas and the large scale structural features of the Milky Way such as the spiral arms, Galactic bar and Galactic centre. We find that approximately 60 per cent of the molecular gas is associated with the spiral arms and these appear as strong intensity peaks in the derived Galactocentric distribution. We also find strong peaks in intensity at specific longitudes that correspond to the Galactic centre and well known star forming complexes, revealing that the 13CO emission is concentrated in a small number of complexes rather than evenly distributed along spiral arms.

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