Search

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., Comment: 11 pages, 11 figures, accepted for publication in A&A

The expanding molecular ring (EMR) manifests itself as a parallelogram in the position-velocity diagram of spectral line emission from the Central Molecular Zone (CMZ) surrounding the Galacic centre (GC). Using multiwavelength data, we investigate the gas kinematics, star formation activity, and the presence of shocked gas in a 200 pc long high velocity gas stream (V~ +150 km/s) with a double helix morphology named the helix stream, that is located 15-55 pc above the CMZ and is kinematically associated with the EMR/parallelogram. We carried out molecular line observations using the IRAM 30m, Yebes 40m, and APEX 12m telescopes. The detection of four rotational transitions of the SiO molecule indicate the presence of shocks. We derived the SiO column densities and abundances in different regions of the helix stream. The presence of protostellar clumps and a candidate HII region signify the ongoing star formation activity within the helix stream. The cloud is massive (2.5x10^6 M_sun) and highly turbulent. We find evidence of cloud-cloud collisions towards the eastern edge (l~1.3{\deg}), suggesting a dynamic interaction with the CMZ. An expanding shell is detected within the cloud with radius of 6.7 pc and an expansion velocity of 35 km/s. The shell might be powered by several supernovae or a single hypernova. The SiO abundance within the helix stream implies extensive shock processes occurring on large scales. The helical or cork-screw velocity structure of the helix stream indicates twisting and turning motions within the cloud. We propose that the helix stream is the continuation of the near side bar lane, that is overshooting after brushing the CMZ. Our findings carry profound implications for understanding star formation in extreme conditions and elucidate the intricate properties of gas and dust associated with nuclear inflows in barred spiral galaxies., Comment: 20 pages, 20 figures, 4 tables, accepted for publication in A&A

To study the impact of the initial effects of metallicity (i.e., the abundance of elements heavier than helium) on star formation and the formation of different molecular species, we searched for hot molecular cores in the sub-solar metallicity environment of the Large Magellanic Cloud (LMC). We conducted an ALMA Band 6 observations of 20 fields centered on young stellar objects (YSOs) distributed over the LMC in order to search for hot molecular cores in this galaxy. We detected a total of 65 compact 1.2 mm continuum cores in the 20 ALMA fields and analyzed their spectra with XCLASS software. The main temperature tracers are CH3OH and SO2, with more than two transitions detected in the observed frequency ranges. Other molecular lines with high detection rates in our sample are CS , SO, H13CO+, H13CN, HC15 N, and SiO. More complex molecules, such as HNCO, HDCO, HC3N, CH3CN, and NH2CHO, and multiple transitions of SO and SO2 isotopologues showed tentative or definite detection toward a small subset of the cores. According to the chemical richness of the cores and high temperatures from the XCLASS fitting, we report the detection of four hot cores and one hot core candidate. With one new hot core detection in this study, the number of detected hot cores in the LMC increases to seven. Six out of seven hot cores detected in the LMC to date are located in the stellar bar region of this galaxy. These six hot cores show emission from complex organic molecules (COMs), such as CH3OH, CH3CN, CH3OCHO, and CH3OCH3. The only known hot core in the LMC with no detection of COMs is located outside the bar region. The metallicity in the LMC presents a shallow gradient increasing from outer regions toward the bar. We suggest that the formation of hot molecular cores containing COMs ensues from the new generation of stars forming in the more metal-rich environment of the LMC bar.

The Next Generation Very Large Array (ngVLA) is a planned radio interferometer providing unprecedented sensitivity at wavelengths between 21 cm and 3 mm. Its 263 antenna element array will be spatially distributed across North America to enable both superb low surface brightness recovery and sub-milliarcsecond angular resolution imaging. The project was developed by the international astronomy community under the lead of the National Radio Astronomy Observatory (NRAO), and is anticipated to be built between 2027 and 2037. Two workshops have been held in 2022 and 2023 with the goal to discuss and consolidate the scientific interests in the ngVLA within the German astronomical community. This community paper constitutes a collection of 48 science ideas which the German community aims to pursue with the ngVLA in the 2030s. This is not a complete list and the ideas are not developed at the level of a "Science Book", such that the present document is mainly meant provide a basis for further discussion within the community. As such, additional contributions are welcome, and will be considered for inclusion in future revisions., Comment: Version 2.0 (status June 18, 2024): 169 pages, comments and future contributions welcome [v2.0: 7 new science cases added, some minor revisions to other chapters]

The application of silicon monoxide (SiO) as a shock tracer arises from its propensity to occur in the gas phase as a result of shock-induced phenomena, including outflow activity and interactions between molecular clouds and expanding HII regions or supernova remnants. We searched for indications of shocks toward 366 massive star-forming regions by observing the ground rotational transition of SiO ($v=0$, $J=1-0$) at 43 GHz with the Korean VLBI Network (KVN) 21 m telescopes to extend our understanding on the origins of SiO in star-forming regions. We detected SiO emission toward 104 regions that consist of 57 IRDCs, 21 HMPOs, and 26 UCHIIs. The determined median SiO column density, $N$(SiO), and abundance, $X$(SiO), relative to $N$(H$_2$) are $8.12\times10^{12}$ cm$^{-2}$ and $1.28\times10^{-10}$, respectively. These values are similar to those obtained toward other star-forming regions and also consistent with predicted values from shock models with low-velocity shocks ($\lesssim$10 - 15 km s$^{-1}$). While the $X$(SiO) does not exhibit any strong correlation with the evolutionary stages of their host clumps, $L_{\rm SiO}$ is highly correlated with dust clump mass, and $L_{\rm SiO}/L_{\rm bol}$ also has a strong negative correlation with $T_{\rm dust}$. This shows that colder and younger clumps have high $L_{\rm SiO}/L_{\rm bol}$ suggestive of an evolutionary trend. This trend is not due to excess emission at higher velocities, such as SiO wing features, as the colder sources with high $L_{\rm SiO}/L_{\rm bol}$ ratios lack wing features. Comparing SiO emission with H$_2$O and Class I CH$_3$OH masers, we find a significant correlation between $L_{\rm SiO}$/$L_{\rm bol}$ and $L_{\rm CH_3OH}/L_{\rm bol}$ ratios, whereas no similar correlation is seen for the H$_2$O maser emission. This suggests a similar origin for the SiO and Class I CH$_3$OH emission in these sources., Comment: 23 pages, 16 figures, accepted for A&A for publication

We present 500 AU and 700 AU resolution 1 mm and 3 mm ALMA observations, respectively, of protostellar cores in protoclusters Sagittarius B2 (Sgr B2) North (N) and Main (M), parts of the most actively star-forming cloud in our Galaxy. Previous lower resolution (5000 AU) 3 mm observations of this region detected $\sim$150 sources inferred to be young stellar objects (YSOs) with $M>8\mathrm{\,M}_\odot$. With a tenfold increase in resolution, we detect 371 sources at 3 mm and 218 sources in the smaller field of view at 1 mm. The sources seen at low resolution are observed to fragment into an average of two objects. About a third of the observed sources fragment. Most of the sources we report are marginally resolved and are at least partially optically thick. We determine that the observed sources are most consistent with Stage 0/I YSOs, i.e., rotationally supported disks with an active protostar and an envelope, that are warmer than those observed in the solar neighborhood. We report source-counting-based inferred stellar mass and the star formation rate of the cloud: 2800$\mathrm{\,M}_\odot$, 0.0038$\mathrm{\,M}_\odot$ yr$^{-1}$ for Sgr B2 N and 6900$\mathrm{\,M}_\odot$, 0.0093$\mathrm{\,M}_\odot$ yr$^{-1}$ for Sgr B2 M respectively., Comment: 31 pages, 18 figures. Accepted for publication in ApJ (September 15, 2023)

The role of massive ($\geq$ 8M$_{\odot}$) stars in defining the energy budget and chemical enrichment of the interstellar medium in their host galaxy is significant. In this first paper from the Tracing Evolution in Massive Protostellar Objects (TEMPO) project we introduce a colour-luminosity selected (L$_*$ $\sim$ 3$\times10^3$ to 1$\times10^5$ L$_{\odot}$) sample of 38 massive star forming regions observed with ALMA at 1.3mm and explore the fragmentation, clustering and flux density properties of the sample. The TEMPO sample fields are each found to contain multiple fragments (between 2-15 per field). The flux density budget is split evenly (53%-47%) between fields where emission is dominated by a single high flux density fragment and those in which the combined flux density of fainter objects dominates. The fragmentation scales observed in most fields are not comparable with the thermal Jeans length, $\lambda_J$, being larger in the majority of cases, suggestive of some non-thermal mechanism. A tentative evolutionary trend is seen between luminosity of the clump and the `spectral line richness' of the TEMPO fields; with 6.7GHz maser associated fields found to be lower luminosity and more line rich. This work also describes a method of line-free continuum channel selection within ALMA data and a generalised approach used to distinguishing sources which are potentially star-forming from those which are not, utilising interferometric visibility properties., Comment: 42 pages, 17 figures, 4 Tables including 3 Appendices (with additional tables and figures). Accepted for publication in MNRAS

We report the first extragalactic detection of the higher-order millimeter hydrogen recombination lines ($\Delta n>2$). The $\gamma$-, $\epsilon$-, and $\eta$-transitions have been detected toward the millimeter continuum source N105-1A in the star-forming region N105 in the Large Magellanic Cloud (LMC) with the Atacama Large Millimeter/submillimeter Array (ALMA). We use the H40$\alpha$ line, the brightest of the detected recombination lines (H40$\alpha$, H36$\beta$, H50$\beta$, H41$\gamma$, H57$\gamma$, H49$\epsilon$, H53$\eta$, and H54$\eta$), and/or the 3 mm free-free continuum emission to determine the physical parameters of N105-1A (the electron temperature, emission measure, electron density, and size) and study ionized gas kinematics. We compare the physical properties of N105-1A to a large sample of Galactic compact and ultracompact (UC) H II regions and conclude that N105-1A is similar to the most luminous ($L>10^5$ $L_{\odot}$) UC H II regions in the Galaxy. N105-1A is ionized by an O5.5 V star, it is deeply embedded in its natal molecular clump, and likely associated with a (proto)cluster. We incorporate high-resolution molecular line data including CS, SO, SO$_2$, and CH$_3$OH ($\sim$0.12 pc), and HCO$^{+}$ and CO ($\sim$0.087 pc) to explore the molecular environment of N105-1A. Based on the CO data, we find evidence for a cloud-cloud collision that likely triggered star formation in the region. We find no clear outflow signatures, but the presence of filaments and streamers indicates on-going accretion onto the clump hosting the UC H II region. Sulfur chemistry in N105-1A is consistent with the accretion shock model predictions., Comment: 51 pages, 30 figures, 2 tables (including appendices); accepted for publication in The Astrophysical Journal (ApJ)

Sagittarius B2 (Sgr B2) is a giant molecular cloud complex in the central molecular zone of our Galaxy hosting several sites of high-mass star formation. The two main centers of activity are Sgr B2(M) and Sgr B2(N), which contain 27 and 20 continuum sources, respectively. Our analysis aims to be a comprehensive modeling of each core spectrum, where we take the complex interaction between molecular lines, dust attenuation, and free-free emission arising from HII regions into account. In this work, we determine the dust and, if HII regions are contained, the parameters of the free-free thermal emission of the ionized gas for each core, and derive a self-consistent description of the continuum levels of each core. Using the high sensitivity of ALMA, we characterize the physical and chemical structure of these continuum sources and gain better insight into the star formation process within the cores. We used ALMA to perform an unbiased spectral line survey of all 47 sources in ALMA band 6 with a frequency coverage from 211 GHz to 275 GHz. In order to model the free-free continuum contribution of a specific core, we fit the contained recombination lines (RRLs) to obtain the electron temperatures and the emission measures, where we use an extended XCLASS program to describe RRLs and free-free continuum simultaneously. In contrast to previous analyses, we derived the corresponding parameters here not only for each core, but also for their local surrounding envelope, and determined their physical properties. The distribution of RRLs we found in the core spectra closely fits the distribution of HII regions described in previous analyses. For the cores we determine average dust temperatures of around 236 K (Sgr B2(M)) and 225 K (Sgr B2(N)), while the electronic temperatures are located in a range between 3800 K and 23800 K.

The G31.41+0.31 Unbiased ALMA sPectral Observational Survey (GUAPOS) project targets the hot molecular core (HMC) G31.41+0.31 (G31), to unveil the complex chemistry of one of the most chemically rich high-mass star-forming regions outside the Galactic Center (GC). In the third paper of the project, we present a study of nine O-bearing (CH$_3$OH, $^{13}$CH$_3$OH, CH$_3^{18}$OH, CH$_3$CHO, CH$_3$OCH$_3$, CH$_3$COCH$_3$ , C$_2$H$_5$OH, aGg'-(CH$_2$OH)$_2$, and gGg'-(CH$_2$OH)$_2$) and six N-bearing (CH$_3$CN, $^{13}$CH$_3$CN, CH$_3^{13}$CN, C$_2$H$_3$CN, C$_2$H$_5$CN, and C$_2$H$_5^{13}$CN) complex organic molecules toward G31. The aim of this work is to characterize the abundances in one of the most chemically-rich hot molecular cores outside the GC and to search for a possible chemical segregation between O-bearing and N-bearing species in G31, which hosts four compact sources as seen with higher angular resolution data. Observations were carried out with the interferometer ALMA and covered the entire Band 3 from 84 to 116 GHz ($\sim 32$ GHz bandwidth) with an angular resolution of $1.2''$ ($\sim4400\,\mathrm{au}$). The spectrum has been analyzed with the tool SLIM of MADCUBA to determine the physical parameters of the emitting gas. Moreover, we have analyzed the morphology of the emission of the molecular species. We have compared the abundances w.r.t methanol of COMs in G31 with other twenty-seven sources, including other hot molecular cores inside and outside the Galactic Center, hot corinos, shocked regions, envelopes around young stellar objects, and quiescent molecular clouds, and with chemical models. Different species peak at slightly different positions, and this, together with the different central velocities of the lines obtained from the spectral fitting, point to chemical differentiation of selected O-bearing species., Comment: accepted for publication in A&A, 39 pages

We report the discovery of a velocity coherent, funnel shaped ^13CO emission feature in the Galactic centre (GC) using data from the SEDIGISM survey. The molecular cloud appears as a low velocity structure (V_LSR=[-3.5, +3.5] km/s) with an angular extent of 0.95{\deg} x 1{\deg}, extending toward positive Galactic latitudes. The structure is offset from Sgr A* toward negative Galactic longitudes and spatially and morphologically correlates well with the northern lobe of the 430 pc radio bubble, believed to be the radio counterpart of the multiwavelength GC chimney. Spectral line observations in the frequency range of 85-116 GHz have been carried out using the IRAM 30 metre telescope toward 12 positions along the funnel-shaped emission. We examine the ^12C/^13C isotopic ratios using various molecules and their isotopologues. The mean ^12C/^13C isotope ratio (30.6+-2.9) is consistent with the structure located within inner 3 kpc of the Galaxy and possibly in the GC. The velocity of the molecular funnel is consistent with previous radio recombination line measurements of the northern lobe of radio bubble. Our multiwavelength analysis suggests that the funnel shaped structure extending over 100 pc above the Galactic plane is the molecular counterpart of the northern GC chimney., Comment: Accepted for publication in A&A Letters

A substantial fraction of oxygen in diffuse clouds is unaccounted for by observations and is postulated to be in an unknown refractory form, referred to as unidentified depleted oxygen (UDO), which, depending on the local gas density, may contribute up to 50% of the total oxygen content. Previous Infrared Space Observatory (ISO) observations suggest that a significant fraction of oxygen in even denser, translucent clouds may be in atomic form. We have analyzed velocity-resolved archival SOFIA observations of the 63 $\mu$m fine-structure [O I] transition toward the high-mass star-forming region Sgr B2(M) in the Central Molecular Zone. The foreground spiral-arm clouds as well as the extended Sgr B2 envelope between the Sun and the background dust continuum source produce multiple [O i] absorption components, spectrally separated in velocity space. The gas-phase atomic oxygen column density in foreground clouds toward Sgr B2 is well correlated with the total hydrogen column density, with an average atomic oxygen abundance of $(2.51 \pm 0.69) \times 10^{-4}$ with respect to hydrogen nuclei. This value is in good agreement with the earlier ISO measurements on the same line of sight, and is about 35% lower than the total interstellar medium oxygen abundance in the low-density warm gas, as measured in the UV. We find no evidence that a significant fraction of the oxygen on the line of sight toward Sagittarius B2 is in the form of UDO., Comment: 7 pages, 7 figures, and 2 appendices. Astronomy & Astrophysics Letters, in press

As a complement to the HyGAL Stratospheric Observatory for Infrared Astronomy Legacy Program, we report the results of a ground-based absorption line survey of simple molecules in diffuse and translucent Galactic clouds. Using the Institut de Radioastronomie Millim\'etrique (IRAM) 30 m telescope, we surveyed molecular lines in the 2 mm and 3 mm wavelength ranges toward 15 millimeter continuum sources. These sources, which are all massive star-forming regions located mainly in the first and second quadrants of the Milky Way, form the subset of the HyGAL sample that can be observed by the IRAM 30 m telescope. We detected HCO$^+$ absorption lines toward 14 sightlines, toward which we identified 78 foreground cloud components, as well as lines from HCN, HNC, C$_2$H, and c-C$_3$H$_2$ toward most sightlines. In addition, CS and H$_2$S absorption lines are found toward at least half of the continuum sources. Static Meudon photodissociation region (PDR) isobaric models that consider ultraviolet-dominated chemistry were unable to reproduce the column densities of all seven molecular species by just a factor of a few, except for H$_2$S. The inclusion of other formation routes driven by turbulent dissipation could possibly explain the observed high column densities of these species in diffuse clouds. There is a tentative trend for H$_2$S and CS abundances relative to H$_2$ to be larger in diffuse clouds ($X$(H$_2$S) and $X$(CS) $\sim 10^{-8} - 10^{-7}$) than in translucent clouds ($X$(H$_2$S) and $X$(CS) $\sim 10^{-9} - 10^{-8}$) toward a small sample; however, a larger sample is required in order to confirm this trend. The derived H$_2$S column densities are higher than the values predicted from the isobaric PDR models, suggesting that chemical desorption of H$_2$S from sulfur-containing ice mantles may play a role in increasing the H$_2$S abundance., Comment: 41 pages, 25 figures, 10 tables, and 5 appendices. Accepted for publication in A&A

No statistical study of COMs toward a large sample of high-mass protostars with ALMA has been carried out so far. We aim to study six N-bearing species: CH$_3$CN, HNCO, NH$_2$CHO, C$_2$H$_5$CN, C$_2$H$_3$CN and CH$_3$NH$_2$ in a large sample of high-mass protostars. From the ALMAGAL survey, 37 of the most line-rich hot molecular cores are selected. Next, we fit their spectra and find column densities and excitation temperatures of the above N-bearing species, in addition to CH$_3$OH. We (tentatively) detect CH$_3$NH$_2$ in $\sim32%$ of the sources. We find three groups of species when comparing their excitation temperatures: hot (NH$_2$CHO; Tex > 250 K), warm (C$_2$H$_3$CN, HN$^{13}$CO and CH$_{3}^{13}$CN; 100 K < Tex < 250 K) and cold species (CH$_3$OH and CH$_3$NH$_2$; Tex < 100 K). This temperature segregation reflects the trend seen in their sublimation temperatures and validates the idea of onion-like structure of COMs around protostars. Moreover, the molecules studied here show constant column density ratios across low- and high-mass protostars with scatter less than a factor $\sim3$ around the mean. The constant column density ratios point to a common formation environment of COMs or their precursors, most likely in the pre-stellar ices. The scatter around the mean of the ratios, although small, varies depending on the species considered. This spread can either have a physical origin (source structure, line or dust optical depth) or a chemical one. Formamide is most prone to the physical effects as it is tracing the closest regions to the protostars, whereas such effects are small for other species. Assuming that all molecules form in the pre-stellar ices, the scatter variations could be explained by differences in lifetimes or physical conditions of the pre-stellar clouds. If the pre-stellar lifetimes are the main factor, they should be similar for low- and high-mass protostars., Comment: 49 pages, 46 figures, Accepted for publication in A&A

The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. Two ultra-compact HII (UCHII) regions were identified in SgrB2's central hot cores, SgrB2(M) and SgrB2(N). Our aim is to characterize the properties of the HII regions in the entire SgrB2 cloud. Comparing the HII regions and the dust cores, we aim to depict the evolutionary stages of different parts of SgrB2. We use the Very Large Array in its A, CnB, and D configurations, and in the frequency band C (~6 GHz) to observe the whole SgrB2 complex. Using ancillary VLA data at 22.4 GHz and ALMA data at 96 GHz, we calculated the physical parameters of the UCHII regions and their dense gas environment. We identify 54 UCHII regions in the 6 GHz image, 39 of which are also detected at 22.4 GHz. Eight of the 54 UCHII regions are newly discovered. The UCHII regions have radii between $0.006 {\rm pc}$ and $0.04 {\rm pc}$, and have emission measure between $10^{6} {\rm pc\,cm^{-6}}$ and $10^{9} {\rm pc\,cm^{-6}}$. The UCHII regions are ionized by stars of types from B0.5 to O6. We found a typical gas density of $\sim10^6-10^9 {\rm cm^{-3}}$ around the UCHII regions. The pressure of the UCHII regions and the dense gas surrounding them are comparable. The expansion timescale of these UCHII regions is determined to be $\sim10^4-10^5 {\rm yr}$. The percentage of the dust cores that are associated with HII regions are 33%, 73%, 4%, and 1% for SgrB2(N), SgrB2(M), SgrB2(S), and SgrB2(DS), respectively. Two-thirds of the dust cores in SgrB2(DS) are associated with outflows. The electron densities of the UCHII regions we identified are in agreement with that of typical UCHII regions, while the radii are smaller than those of the typical UCHII regions. The dust cores in SgrB2(N) are more evolved than in SgrB2(DS) but younger than in SgrB2(M)., Comment: 17 pages, 15 figure, accepted to A&A

The deuteration of molecules forming in the ices such as methanol (CH$_3$OH) is sensitive to the physical conditions during their formation in dense cold clouds and can be probed through observations of deuterated methanol in hot cores. Observations with ALMA containing transitions of CH$_3$OH, CH$_2$DOH, CHD$_2$OH, $^{13}$CH$_3$OH, and CH$_3^{18}$OH are investigated. The column densities of CH$_2$DOH, CHD$_2$OH, and CH$_3$OH are determined for all sources, where the column density of CH$_3$OH is derived from optically thin $^{13}$C and $^{18}$O isotopologues. Consequently, the D/H ratio of methanol is derived taking statistical effects into account. Singly deuterated methanol (CH$_2$DOH) is detected toward 25 of the 99 sources in our sample of the high-mass protostars. Including upper limits, the $\rm (D/H)_{CH_3OH}$ ratio inferred from $N_\mathrm{CH_2DOH}/N_\mathrm{CH_3OH}$ was derived for 38 of the 99 sources and varies between $\sim10^{-3}-10^{-2}$. Including other high-mass hot cores from the literature, the mean methanol D/H ratio is $1.1\pm0.7\times10^{-3}$. This is more than one order of magnitude lower than what is seen for low-mass protostellar systems ($2.2\pm1.2\times10^{-2}$). Doubly deuterated methanol (CHD$_2$OH) is detected toward 11 of the 99 sources. Including upper limits for 15 sources, the $\rm (D/H)_{CH_2DOH}$ ratios derived from $N_\mathrm{CHD_2OH}/N_\mathrm{CH_2DOH}$ are more than two orders of magnitude higher than $\rm (D/H)_{CH_3OH}$ with an average of $2.0\pm0.8\times10^{-1}$ which is similar to what is found for low-mass sources. Comparison with literature GRAINOBLE models suggests that the high-mass prestellar phases are either warm ($>20$ K) or live shorter than the free-fall timescale. In contrast, for low-mass protostars, both a low temperature of $<15$ K and a prestellar phase timescale longer than the free-fall timescale are necessary., Comment: 17 pages, 9 figures, accepted to A&A

We report the first detection of deuterated water (HDO) toward an extragalactic hot core. The HDO 2$_{11}$-2$_{12}$ line has been detected toward hot cores N105-2A and 2B in the N105 star-forming region in the low-metallicity Large Magellanic Cloud (LMC) dwarf galaxy with the Atacama Large Millimeter/submillimeter Array (ALMA). We have compared the HDO line luminosity ($L_{\rm HDO}$) measured toward the LMC hot cores to those observed toward a sample of seventeen Galactic hot cores covering three orders of magnitude in $L_{\rm HDO}$, four orders of magnitude in bolometric luminosity ($L_{\rm bol}$), and a wide range of Galactocentric distances (thus metallicities). The observed values of $L_{\rm HDO}$ for the LMC hot cores fit very well into the $L_{\rm HDO}$ trends with $L_{\rm bol}$ and metallicity observed toward the Galactic hot cores. We have found that $L_{\rm HDO}$ seems to be largely dependent on the source luminosity, but metallicity also plays a role. We provide a rough estimate of the H$_2$O column density and abundance ranges toward the LMC hot cores by assuming that HDO/H$_2$O toward the LMC hot cores is the same as that observed in the Milky Way; the estimated ranges are systematically lower than Galactic values. The spatial distribution and velocity structure of the HDO emission in N105-2A is consistent with HDO being the product of the low-temperature dust grain chemistry. Our results are in agreement with the astrochemical model predictions that HDO is abundant regardless of the extragalactic environment and should be detectable with ALMA in external galaxies., Comment: 21 pages, 2 tables, 9 figures (including appendices); Accepted for publication in the Astrophysical Journal

The HyGAL SOFIA legacy program surveys six hydride molecules -- ArH+, OH+, H2O+, SH, OH, and CH -- and two atomic constituents -- C+ and O -- within the diffuse interstellar medium (ISM) by means of absorption-line spectroscopy toward 25 bright Galactic background continuum sources. This detailed spectroscopic study is designed to exploit the unique value of specific hydrides as tracers and probes of different phases of the ISM, as demonstrated by recent studies with the Herschel Space Observatory. The observations performed under the HyGAL program will allow us to address several questions related to the lifecycle of molecular material in the ISM and the physical processes that impact its phase transition, such as: (1) What is the distribution function of the H2 fraction in the ISM? (2) How does the ionization rate due to low-energy cosmic-rays vary within the Galaxy? (3) What is the nature of interstellar turbulence, and what mechanisms lead to its dissipation? This overview discusses the observing strategy, synergies with ancillary and archival observations, the data reduction and analysis schemes adopted; and presents the first results obtained toward three of the survey targets, W3(OH), W3IRS5 and NGC7538IRS1. Robust measurements of the column densities of these hydrides -- obtained through widespread observations of absorption lines-- help address the questions raised, and there is a timely synergy between these observations and the development of theoretical models, particularly pertaining to the formation of H2 within the turbulent ISM. The provision of enhanced HyGAL data products will therefore serve as a legacy for future ISM studies., Comment: 33 pages, 17 figures, 7 tables. Accepted for publication in the Astrophysical Journal

Complex organic molecules (COMs) are often observed toward embedded Class 0 and I protostars. However, not all Class 0 and I protostars exhibit COMs emission. In this work, variations in methanol (CH$_3$OH) emission are studied to test if absence of CH$_3$OH emission can be linked to source properties. Combining both new and archival observations with ALMA and sources from the literature, a sample of 184 low-mass and high-mass protostars is investigated. The warm (T > 100 K) gaseous CH$_3$OH mass, $M_{\rm CH_3OH}$, is determined for each source using primarily optically thin isotopologues. On average, Class I protostellar systems seem to have less warm $M_{\rm CH_3OH}$ ($<10^{-10}$ M$_\odot$) than younger Class 0 sources ($\sim10^{-7}$ M$_\odot$). High-mass sources in our sample show higher warm $M_{\rm CH_3OH}$ up to $10^{-7}-10^{-3}$ M$_\odot$. To take into account the effect of the source's overall mass on $M_{\rm CH_3OH}$, a normalized CH$_3$OH mass is defined as $M_{\rm CH_3OH}/M_{\rm dust,0}$, where $M_{\rm dust,0}$ is the cold + warm dust mass within a fixed radius. Excluding upper limits, a simple power-law fit to the normalized warm CH$_3$OH masses results in $M_{\rm CH_3OH}/M_{\rm dust,0}\propto L_{\rm bol}^{0.70\pm0.05}$. This is in good agreement with a simple hot core toy model which predicts that the normalized $M_{\rm CH_3OH}$ increases with $L_{\rm bol}^{0.75}$ due to the snowline moving outward. Sources for which the size of the disk is equivalent or smaller than the estimated 100 K radius agree well with the best-fit power-law model, whereas sources with significantly larger disks show up to two orders of magnitude lower normalized warm CH$_3$OH masses. Based on the latter results, we suggest that source structure such as a disk can result in colder gas and thus fewer COMs in the gas phase. Additionally, optically thick dust can hide the emission of COMs., Comment: 22 pages, 6 figures, accepted for publication in A&A

Context. To better understand the formation of high-mass stars, it is fundamental to investigate how matter accretes onto young massive stars, how it is ejected, and how all this differs from the low-mass case. The massive protocluster G31.41+0.31 is the ideal target to study all these processes because observations at millimeter and centimeter wavelengths have resolved the emission of the Main core into at least four massive dust continuum sources, named A, B, C, and D, within 1" or 0.018 pc, and have identified signatures of infall and several outflows associated with the core. Aims. We study the interplay between infall and outflow in G31.41+0.31 by investigating at a spatial resolution of a few 100 au their properties and their possible impact on the core. Methods. We carried out molecular line observations of typical high-density tracers, such as CH3CN or H2CO, and shock and outflow tracers, such as SiO, with ALMA at 1.4 mm that achieved an angular resolution of 0.09" (340 au). Results. The observations have revealed inverse P-Cygni profiles in CH3CN and H2CO toward the four sources embedded in the Main core, suggesting that all of them are undergoing collapse. The infall rates, estimated from the red-shifted absorption are on the order of 1E-2 Msun/yr. The individual infall rates imply that the accretion timescale of the Main core is an order of magnitude smaller than its rotation timescale. This confirms that rotating toroids such as the G31 Main core are non-equilibrium, transient collapsing structures that need to be constantly replenished with fresh material from a large-scale reservoir. For sources B, C, and D, the infall could be accelerating inside the sources, while for source A, the presence of a second emission component complicates the interpretation. The SiO observations have revealed the presence of at least six outflows in the G31.41+0.31 star-forming region, ..., Comment: 17 pages, 9 figures, 2 tables. Accepted by A&A

The Large Magellanic Cloud (LMC) is the nearest laboratory for detailed studies on the formation and survival of complex organic molecules (COMs), including biologically important ones, in low-metallicity environments--typical for earlier cosmological epochs. We report the results of 1.2 mm continuum and molecular line observations of three fields in the star-forming region N105 with the Atacama Large Millimeter/submillimeter Array (ALMA). N105 lies at the western edge of the LMC bar with on-going star formation traced by H$_2$O, OH, and CH$_3$OH masers, ultracompact H II regions, and young stellar objects. Based on the spectral line modeling, we estimated rotational temperatures, column densities, and fractional molecular abundances for twelve 1.2 mm continuum sources. We identified sources with a range of chemical make-ups, including two bona fide hot cores and four hot core candidates. The CH$_3$OH emission is widespread and associated with all the continuum sources. COMs CH$_3$CN and CH$_3$OCH$_3$ are detected toward two hot cores in N105 together with smaller molecules typically found in Galactic hot cores (e.g., SO$_2$, SO, and HNCO) with the molecular abundances roughly scaling with metallicity. We report a tentative detection of the astrobiologically relevant formamide molecule (NH$_2$CHO) toward one of the hot cores; if confirmed, this would be the first detection of NH$_2$CHO in an extragalactic sub-solar metallicity environment. We suggest that metallicity inhomogeneities resulting from the tidal interactions between the LMC and the Small Magellanic Cloud (SMC) might have led to the observed large variations in COM abundances in LMC hot cores., Comment: 75 pages, 48 figures, 7 tables (including appendices); Accepted for publication in the Astrophysical Journal

[Abridged] The interstellar medium is observed to be organised in filamentary structures, as well as neutral (HI) and ionized (HII) bubbles. The expanding nature of these bubbles makes them shape their surroundings and possibly play a role in the formation and evolution of interstellar filaments. We present APEX $^{13}$CO and C$^{18}$O(2-1) observations of the NGC 6334 molecular cloud. We investigate the gas velocity structure along and across the 50 pc-long cloud and towards 75 identified velocity-coherent-filaments (VCFs). We measure a wealth of velocity gradients along the VCFs. We derive the column density and velocity power spectra of the VCFs. These power spectra are well represented with power laws showing similar slopes for both quantities (with a mean of about -2), albeit some differ by up to a factor of two. The position velocity diagrams perpendicular to three VCFs show the V-shaped velocity pattern, corresponding to a bent structure in velocity space with the filament at the tip of the V surrounded by an extended structure connected to it with a velocity gradient. This velocity structure is qualitatively similar to that resulting from numerical simulations of filament formation from large-scale compression from propagating shock fronts. In addition, the radial profiles perpendicular to these VCFs hint to small-scale internal impacts from neighbouring HII bubbles. The observed opposite curvature in velocity space towards the VCFs points to various origins of large-scale external compressions from propagating HI bubbles. This suggests the plausible importance of multiple HI compressions, separated in space and time, in the formation and evolution of molecular clouds and their star formation history. These latter atomic compressions due to past and distant star formation events are complemented by the impact of HII bubbles from present time and local star formation activity., Comment: Accepted for publication in Astronomy & Astrophysics

We report the discovery of a velocity coherent, kpc-scale molecular structure towards the Galactic center region with an angular extent of 30deg and an aspect ratio of 60:1. The kinematic distance of the CO structure ranges between 4.4 to 6.5 kpc. Analysis of the velocity data and comparison with the existing spiral arm models support that a major portion of this structure is either a sub-branch of the Norma arm or an inter-arm giant molecular filament, likely to be a kpc-scale feather (or spur) of the Milky Way, similar to those observed in nearby spiral galaxies. The filamentary cloud is at least 2.0 kpc in extent, considering the uncertainties in the kinematic distances, and it could be as long as 4 kpc. The vertical distribution of this highly elongated structure reveals a pattern similar to that of a sinusoidal wave. The exact mechanisms responsible for the origin of such a kpc-scale filament and its wavy morphology remains unclear. The distinct wave-like shape and its peculiar orientation makes this cloud, named as the Gangotri wave, one of the largest and most intriguing structures identified in the Milky Way., Comment: 10 pages, 7 figures, accepted for publication in ApJ Letters

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., Comment: 16 pages, 11 figures, Accepted for publication in A&A

Peptide-like bond molecules, which can take part to the formation of proteins in a primitive Earth environment, have been detected up to now only towards a few sources. We present a study of HNCO, HC(O)NH$_{2}$, CH$_{3}$NCO, CH$_{3}$C(O)NH$_{2}$, CH$_{3}$NHCHO, CH$_{3}$CH$_{2}$NCO, NH$_{2}$C(O)NH$_{2}$, NH$_{2}$C(O)CN, and HOCH$_{2}$C(O)NH$_{2}$ towards the hot core G31.41+0.31. We have used the spectrum obtained from the ALMA 3mm spectral survey GUAPOS, with an angular resolution of 1.2"$\times$1.2" ($\sim$4500 au), to derive column densities of all the molecular species, together with other 0.2"$\times$0.2" ($\sim$750 au) ALMA observations to study the morphology of HNCO, HC(O)NH$_{2}$ and CH$_{3}$C(O)NH$_{2}$. We have detected HNCO, HC(O)NH$_{2}$, CH$_{3}$NCO, CH$_{3}$C(O)NH$_{2}$, and CH$_{3}$NHCHO, for the first time all together outside the Galactic center. We have obtained molecular fractional abundances with respect to H$_{2}$ from 10$^{-7}$ down to a few 10$^{-9}$ and with respect to CH$_{3}$OH from 10$^{-3}$ to $\sim$4$\times$10$^{-2}$. From the comparison with other sources, we find that regions in an earlier stage of evolution, such as pre-stellar cores, show abundances at least two orders of magnitude lower than those in hot cores, hot corinos or shocked regions. Moreover, molecular abundance ratios towards different sources are found to be consistent between them within $\sim$1 order of magnitude, regardless of the physical properties (e.g. different masses and luminosities), or the source position throughout the Galaxy. New correlations between pairs of molecular abundances have also been found. These results suggest that all these species are formed on grain surfaces in early evolutionary stages of molecular clouds, and that they are subsequently released back to the gas-phase through thermal desorption or shock-triggered desorption., Comment: 51 pages, 24 figures, 5 tables, 5 appendix - Accepted for publication in A&A

We present a detailed overview of the science goals and predictions for the Prime-Cam direct detection camera/spectrometer being constructed by the CCAT-prime collaboration for dedicated use on the Fred Young Submillimeter Telescope (FYST). The FYST is a wide-field, 6-m aperture submillimeter telescope being built (first light in mid-2024) by an international consortium of institutions led by Cornell University and sited at more than 5600 meters on Cerro Chajnantor in northern Chile. Prime-Cam is one of two instruments planned for FYST and will provide unprecedented spectroscopic and broadband measurement capabilities to address important astrophysical questions ranging from Big Bang cosmology through reionization and the formation of the first galaxies to star formation within our own Milky Way galaxy. Prime-Cam on the FYST will have a mapping speed that is over ten times greater than existing and near-term facilities for high-redshift science and broadband polarimetric imaging at frequencies above 300 GHz. We describe details of the science program enabled by this system and our preliminary survey strategies., Comment: 61 pages, 16 figures. Resubmitted to ApJSS July 11, 2022

We have revisited the chemistry of chlorine-bearing species in the diffuse interstellar medium with new observations of the HCl$^+$ molecular ion and new astrochemical models. Using the GREAT instrument on board SOFIA, we observed the $^2\Pi_{3/2}\, J = 5/2 - 3/2$ transition of HCl$^+$ near 1444 GHz toward the bright THz continuum source W49N. We detected absorption by diffuse foreground gas unassociated with the background source, and were able to thereby measure the distribution of HCl$^+$ along the sight-line. We interpreted the observational data using an updated version of an astrochemical model used previously in a theoretical study of Cl-bearing interstellar molecules. The abundance of HCl$^+$ was found to be almost constant relative to the related H$_2$Cl$^+$ ion, but the observed $n({\rm H_2Cl^+})/n({\rm HCl^+})$ abundance ratio exceeds the predictions of our astrochemical model by an order-of-magnitude. This discrepancy suggests that the rate of the primary destruction process for ${\rm H_2Cl^+}$, dissociative recombination, has been significantly overestimated. For HCl$^+$, the model predictions can provide a satisfactory fit to the observed column densities along the W49N sight-line while simultaneously accounting for the ${\rm OH^+}$ and ${\rm H_2O^+}$ column densities., Comment: 34 pages. 8 figures. Accepted for publication in the Astrophysical Journal

We present a full analysis of a broadband spectral line survey of Sagittarius B2 (Main), one of the most chemically rich regions in the Galaxy located within the giant molecular cloud complex Sgr B2 in the Central Molecular Zone. Our goal is to derive the molecular abundances and temperatures of the high-mass star-forming region Sgr B2(M) and thus its physical and astrochemical conditions. Sgr B2(M) was observed using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory in a spectral line survey from 480 to 1907 GHz at a spectral resolution of 1.1 MHz, which provides one of the largest spectral coverages ever obtained toward this high-mass star-forming region in the submillimeter with high spectral resolution and includes frequencies > 1 THz unobservable from the ground. We model the molecular emission from the submillimeter to the far-IR using the XCLASS program. For each molecule, a quantitative description was determined taking all emission and absorption features of that species across the entire spectral range into account. Additionally, we derive velocity resolved ortho / para ratios for those molecules for which ortho and para resolved molecular parameters are available. Finally, the temperature and velocity distributions are analyzed and the derived abundances are compared with those obtained for Sgr B2(N) from a similar HIFI survey. A total of 92 isotopologues were identified, arising from 49 different molecules, ranging from free ions to complex organic compounds and originating from a variety of environments from the cold envelope to hot and dense gas within the cores. Sulfur dioxide, methanol, and water are the dominant contributors. For the ortho / para ratios we find deviations from the high temperature values between 13 and 27 %. In total 14 % of all lines remain unidentified., Comment: 67 pages, 102 figures, submitted to A&A

We present the $360^\circ$ catalogue of physical properties of Hi-GAL compact sources, detected between 70 and 500 $\mu$m. This release not only completes the analogous catalogue previously produced by the Hi-GAL collaboration for $-71^\circ \lesssim \ell \lesssim 67^\circ$, but also meaningfully improves it thanks to a new set of heliocentric distances, 120808 in total. About a third of the 150223 entries are located in the newly added portion of the Galactic plane. A first classification based on detection at 70 $\mu$m as a signature of ongoing star-forming activity distinguishes between protostellar sources (23~per cent of the total) and starless sources, with the latter further classified as gravitationally bound (pre-stellar) or unbound. The integral of the spectral energy distribution, including ancillary photometry from $\lambda=21$ to 1100 $\mu$m, gives the source luminosity and other bolometric quantities, while a modified black body fitted to data for $\lambda \geq 160\, \mu$m yields mass and temperature. All tabulated clump properties are then derived using photometry and heliocentric distance, where possible. Statistics of these quantities are discussed with respect to both source Galactic location and evolutionary stage. No strong differences in the distributions of evolutionary indicators are found between the inner and outer Galaxy. However, masses and densities in the inner Galaxy are on average significantly larger, resulting in a higher number of clumps that are candidates to host massive star formation. Median behaviour of distance-independent parameters tracing source evolutionary status is examined as a function of the Galactocentric radius, showing no clear evidence of correlation with spiral arm positions., Comment: accepted by MNRAS, april 2021

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., Comment: 16 pages, 16 figures, accepted for Astronomy and Astrophysics, a higher-resolution version can also be found at https://www.mpia.de/homes/beuther/papers.html

Context. ALMA observations at 1.4 mm and 0.2'' (750au) angular resolution of the Main core in the high-mass star forming region G31.41+0.31 have revealed a puzzling scenario: on the one hand, the continuum emission looks very homogeneous and the core appears to undergo solid-body rotation, suggesting a monolithic core stabilized by the magnetic field; on the other hand, rotation and infall speed up toward the core center, where two massive embedded free-free continuum sources have been detected, pointing to an unstable core having undergone fragmentation. Aims. To establish whether the Main core is indeed monolithic or its homogeneous appearance is due to a combination of large dust opacity and low angular resolution, we carried out millimeter observations at higher angular resolution and different wavelengths. Methods. We carried out ALMA observations at 1.4 mm and 3.5 mm that achieved angular resolutions of 0.1''(375 au) and 0.075'' (280 au), respectively. VLA observations at 7 mm and 1.3 cm at even higher angular resolution, 0.05'' (190 au) and 0.07'' (260 au), respectively, were also carried out to better study the nature of the free-free continuum sources detected in the core. Results. The millimeter continuum emission of the Main core has been clearly resolved into at least four sources, A, B, C, and D, within 1'', indicating that the core is not monolithic. The deconvolved radii of the dust emission of the sources, estimated at 3.5 mm, are 400-500au, their masses range from 15 to 26 Msun, and their number densities are several 1E9 cm-3. Sources A and B, located closer to the center of the core and separated by 750 au, are clearly associated with two free-free continuum sources, likely thermal radio jets, and are the brightest in the core. The spectral energy distribution of these two sources and their masses and sizes are similar and suggest a common origin., Comment: 18 pages,9 figures, 5 tables. Accepted by A&A

Applying dendrogram analysis to the CARMA-NRO C$^{18}$O ($J$=1--0) data having an angular resolution of $\sim$ 8", we identified 692 dense cores in the Orion Nebula Cluster (ONC) region. Using this core sample, we compare the core and initial stellar mass functions in the same area to quantify the step from cores to stars. About 22 \% of the identified cores are gravitationally bound. The derived core mass function (CMF) for starless cores has a slope similar to Salpeter's stellar initial mass function (IMF) for the mass range above 1 $M_\odot$, consistent with previous studies. Our CMF has a peak at a subsolar mass of $\sim$ 0.1 $M_\odot$, which is comparable to the peak mass of the IMF derived in the same area. We also find that the current star formation rate is consistent with the picture in which stars are born only from self-gravitating starless cores. However, the cores must gain additional gas from the surroundings to reproduce the current IMF (e.g., its slope and peak mass), because the core mass cannot be accreted onto the star with a 100\% efficiency. Thus, the mass accretion from the surroundings may play a crucial role in determining the final stellar masses of stars., Comment: 13 pages, 5 figures, accepted by ApJL

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., Comment: 29 pages, 14 figures, accepted for publication in A&A

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., Comment: MNRAS, in press

We use the 13CO(2-1) emission from the SEDIGISM high-resolution spectral-line survey of the inner Galaxy, to extract the molecular cloud population with a large dynamic range in spatial scales, using the SCIMES algorithm. This work compiles a cloud catalogue with a total of 10663 molecular clouds, 10300 of which we were able to assign distances and compute physical properties. We study some of the global properties of clouds using a science sample, consisting of 6664 well resolved sources and for which the distance estimates are reliable. In particular, we compare the scaling relations retrieved from SEDIGISM to those of other surveys, and we explore the properties of clouds with and without high-mass star formation. Our results suggest that there is no single global property of a cloud that determines its ability to form massive stars, although we find combined trends of increasing mass, size, surface density and velocity dispersion for the sub-sample of clouds with ongoing high-mass star formation. We then isolate the most extreme clouds in the SEDIGISM sample (i.e. clouds in the tails of the distributions) to look at their overall Galactic distribution, in search for hints of environmental effects. We find that, for most properties, the Galactic distribution of the most extreme clouds is only marginally different to that of the global cloud population. The Galactic distribution of the largest clouds, the turbulent clouds and the high-mass star-forming clouds are those that deviate most significantly from the global cloud population. We also find that the least dynamically active clouds (with low velocity dispersion or low virial parameter) are situated further afield, mostly in the least populated areas. However, we suspect that part of these trends may be affected by some observational biases, and thus require further follow up work in order to be confirmed., Comment: 25 pages (+ appendices, 15 pages), 26 figures, MNRAS

By combining two surveys covering a large fraction of the molecular material in the Galactic disk we investigate the role the spiral arms play in the star formation process. We have matched clumps identified by ATLASGAL with their parental GMCs as identified by SEDIGISM, and use these giant molecular cloud (GMC) masses, the bolometric luminosities, and integrated clump masses obtained in a concurrent paper to estimate the dense gas fractions (DGF$_{\rm gmc}=\sum M_{\rm clump}/M_{\rm gmc}$) and the instantaneous star forming efficiencies (i.e., SFE$_{\rm gmc} = \sum L_{\rm clump}/M_{\rm gmc}$). We find that the molecular material associated with ATLASGAL clumps is concentrated in the spiral arms ($\sim$60% found within $\pm$10 km s$^{-1}$ of an arm). We have searched for variations in the values of these physical parameters with respect to their proximity to the spiral arms, but find no evidence for any enhancement that might be attributable to the spiral arms. The combined results from a number of similar studies based on different surveys indicate that, while spiral-arm location plays a role in cloud formation and HI to H$_2$ conversion, the subsequent star formation processes appear to depend more on local environment effects. This leads us to conclude that the enhanced star formation activity seen towards the spiral arms is the result of source crowding rather than the consequence of a any physical process., Comment: 15 pages, 12 figures. Full list of affiliations can be found at the end of the paper

Recent theoretical and observational studies debate the similarities between the formation process of high-mass (>8 Msun) and low-mass stars. The formation of low-mass star formation is directly associated with the presence of disks and jets. According to this scenario, radio jets are expected to be common in high-mass star-forming regions. We aim to increase the number of known radio jets in high-mass star forming regions by searching for radio jet candidates at radio continuum wavelengths. We have used the Karl G. Jansky Very Large Array (VLA) to observe 18 high-mass star-forming regions in the C band (6 cm, ~1.0 arcsec resolution) and K band (1.3 cm, ~0.3 arcsec resolution). We have searched for radio jet candidates by studying the association of radio continuum sources with shock activity signposts. We have identified 7 as the most probable radio jets. The radio luminosity of the radio jet candidates is correlated with the bolometric luminosity and the outflow momentum rate. About 7-36% of the radio jet candidates are associated with non-thermal emission. The radio jet candidates associated with 6.7 GHz CH3OH maser emission are preferentially thermal winds and jets, while a considerable fraction of radio jet candidates associated with H2O masers show non-thermal emission, likely due to strong shocks. Our sample of 18 regions is divided in 8 less evolved, infrared-dark regions and 10 more evolved, infrared-bright regions. We have found that ~71% of the identified radio jet candidates are located in the more evolved regions. Similarly, 25% of the less evolved regions harbor one of the most probable radio jets, while up to 50% of the more evolved regions contain one of these radio jet candidates. This suggests that the detection of radio jets in high-mass star forming regions is larger in slightly more evolved regions., Comment: 40 pages, 165 figures, Accepted by A&A on November 27, 2020

A unique filament is identified in the {\it Herschel} maps of the Orion A giant molecular cloud. The filament, which, we name the Stick, is ruler-straight and at an early evolutionary stage. Transverse position-velocity diagrams show two velocity components closing in on the Stick. The filament shows consecutive rings/forks in C$^{18}$O(1-0) channel maps, which is reminiscent of structures generated by magnetic reconnection. We propose that the Stick formed via collision-induced magnetic reconnection (CMR). We use the magnetohydrodynamics (MHD) code Athena++ to simulate the collision between two diffuse molecular clumps, each carrying an anti-parallel magnetic field. The clump collision produces a narrow, straight, dense filament with a factor of $>$200 increase in density. The production of the dense gas is seven times faster than free-fall collapse. The dense filament shows ring/fork-like structures in radiative transfer maps. Cores in the filament are confined by surface magnetic pressure. CMR can be an important dense-gas-producing mechanism in the Galaxy and beyond., Comment: 39 pages, 31 figures, 2 tables, accepted by ApJ

Understanding the degree of chemical complexity that can be reached in star-forming regions, together with the identification of precursors of the building blocks of life in the interstellar medium, is one of the goals of astrochemistry. Unbiased spectral surveys with large bandwidth and high spectral resolution are thus needed, to resolve line blending in chemically rich sources and identify complex organic molecules. This kind of observations has been successfully carried out, mainly towards the Galactic Center, a region that shows peculiar environmental conditions. We present an unbiased spectral survey at 3mm of one of the most chemically rich hot molecular cores located outside the Galactic Center, in the high-mass star-forming region G31.41+0.31. In this first paper, we present the survey and discuss the detection of the 3 isomers of C$_{2}$H$_{4}$O$_{2}$: methyl formate, glycolaldehyde and acetic acid. Observations were carried out with ALMA and cover the entire Band 3 from 84 to 116 GHz with an angular resolution of $1.2^{''}$x$1.2^{''}$ and a spectral resolution of $\sim0.488$ MHz. The transitions of the 3 molecules have been analyzed with the software XCLASS. All three isomers were detected and methyl formate and acetic acid abundances in G31 are the highest detected up to now, if compared to sources in literature. The size of the emission varies among the three isomers with acetic acid showing the most compact emission while methyl formate the most extended. The comparison with chemical models suggests the necessity of grain-surface routes for the formation of methyl formate in G31, while for glycolaldehyde both scenarios could be feasible. Proposed grain-surface reaction for acetic acid is not able to reproduce the observed abundance in this work, while gas-phase scenario should be further tested due to large uncertainties., Comment: 49 pages, 29 figures, accepted for publication in A&A

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$\alpha$ 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., Comment: Published at https://iopscience.iop.org/article/10.3847/2041-8213/aa7d48/pdf

Io's atmosphere is predominately SO2 sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter's large magnetosphere. Previous studies attributed various transient phenomena in Io's environment and Jupiter's magnetosphere to a sudden change in the mass loss from the atmosphere supposedly triggered by a change in volcanic activity. Since the gas in volcanic plumes does not escape directly, such causal correlation would require a transient volcano-induced change in atmospheric abundance, which has never been observed so far. Here we report four observations of atmospheric SO2 and NaCl obtained with the IRAM NOEMA interferometer. These observations are compared to measurements of volcanic hot spots and Io's neutral and plasma environment. We find a stable NaCl column density in Io's atmosphere. The SO2 column density derived for December 2016 is about 30% lower compared to the period of March to April 2017. This increase in SO2 from December 2016 to March 2017 might be related to increasing volcanic activity observed at several sites in spring 2017, but the stability of the volcanic trace gas NaCl and resulting decrease in NaCl/SO2 ratio do not support this interpretation. Observed dimmings in both the sulfur ion torus and Na neutral cloud suggest rather a decrease in mass loading in the period of increasing SO2 abundance. The dimming Na brightness and stable atmospheric NaCl furthermore dispute an earlier suggested positive correlation of the sodium cloud and the hot spot activity at Loki Patara, which considerably increased in this period. The environment of Io overall appears to be in a quiescent state, preventing further conclusions. Only Jupiter's aurora morphology underwent several short-term changes, which are apparently unrelated to Io's quiescent environment or the relatively stable atmosphere., Comment: 19 pages, 3 figures. Paper published in Icarus. Abstract in arXiv slightly modified with respect to the published version

We have studied the high-mass star-forming complex NGC 6334 with ALMA in the continuum emission at a frequency of 87.6 GHz, achieving a spatial resolution of 1300 au. Detecting 142 compact sources distributed over the whole observed area, we then used machine learning algorithms to group the compact cores in different clusters. A total of four main clusters were identified: NGC 6334-E, NGC 6334-I, NGC 6334-I(N) and NGC 6334-I(NW). The typical separations between cluster members (4000-12000 au) together with the core masses (0.2-100 $M_{\odot}$) are in agreement with turbulent fragmentation at scales of 0.1 pc. We find that the CMFs (core mass functions) show an excess of massive cores compared to the IMF. Typical uncertainties in temperature or unresolved multiplicity may mimic the observed excess of massive cores. Evidence of mass segregation in NGC 6334-I and NGC 6334-I(N), with the most massive cores located closer to the center, was found. Correlations between the physical properties of the clusters and their evolutionary stage were searched for, and found to show a larger separation between cores in the more evolved clusters, favouring the role of gas expulsion and stellar ejection over time. From these results, we suggest that NGC 6334-I(N) was primordially segregated, while NGC 6334-I may have become mass-segregated over time due to dynamical effects. Finally, the lack of massive cores in the most evolved cluster suggests that the gas reservoir may be already exhausted, while the less evolved clusters still have access to a larger gas mass reservoir. In general, the fragmentation in NGC 6334 at large scales (about 1 pc) is governed by turbulent pressure, while at smaller scales (a few hundred au), thermal pressure regulates the fragmentation process., Comment: Accepted for publication in Astronomy & Astrophysics. 20 pages with 15 figures and 3 tables, plus Appendices with extra figures and tables. (Abstract modified)

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., Comment: 22 pages, 13 figures, accepted for publication in A&A