Search

Aims. We aim to investigate the chemistry of internal photon-dominated regions (PDRs) surrounding deeply embedded hypercompact (HC) and ultracompact (UC) HII regions. We search for specific tracers of this evolutionary stage of massive star formation that can be detected with current astronomical facilities. Methods. We modeled hot cores with embedded HC/UCHII regions (called HII region models in the article despite the fact that we do not model the HII region itself), by coupling the astrochemical code Saptarsy to a radiative transfer framework obtaining the spatio-temporal evolution of abundances as well as time-dependent synthetic spectra. In these models where we focused on the internal PDR surrounding the HII region, the gas temperature is set to the dust temperature and we do not include dynamics thus the density structure is fixed. We compared this to hot molecular core (HMC) models and studied the effect on the chemistry of the radiation field which is included in the HII region models only during the computation of abundances. In addition, we investigated the chemical evolution of the gas surrounding HII regions with models of different densities at the ionization front, different sizes of the ionized cavity and different initial abundances. Results. We obtain the time evolution of synthetic spectra for a dozen of selected species as well as ratios of their integrated intensities. We find that some molecules such as C, N2H+, CN, and HCO do not trace the inner core and so are not good tracers to distinguish the HII/PDR regions to the HMCs phase. On the contrary, C+ and O trace the internal PDRs, in the two models starting with different initial abundances, but are unfortunately currently unobservable with the current achievable spatial resolution because of the very thin internal PDR (Δ rPDR < 100 AU). The emission of these two tracers is very dependent on the size of the HII region and on the density in the PDR. In addition, we find that the abundance profiles are highly affected by the choice of the initial abundances, hence the importance to properly define them. [ABSTRACT FROM AUTHOR]

Context. The two hot molecular cores Sgr B2(M) and Sgr B2(N), which are located at the center of the giant molecular cloud complex Sagittarius B2, have been the targets of numerous spectral line surveys, revealing a rich and complex chemistry. Aims. We seek to characterize the physical and chemical structure of the two high-mass star-forming sites SgrB2(M) and SgrB2(N) using high-angular resolution observations at millimeter wavelengths, reaching spatial scales of about 4000 au. Methods. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to perform an unbiased spectral line survey of both regions in the ALMA band 6 with a frequency coverage from 211 GHz to 275 GHz. The achieved angular resolution is 0'.'4, which probes spatial scales of about 4000 au, i.e., able to resolve different cores and fragments. In order to determine the continuum emission in these line-rich sources, we used a new statistical method, STATCONT, which has been applied successfully to this and other ALMA datasets and to synthetic observations. Results. We detect 27 continuum sources in SgrB2(M) and 20 sources in SgrB2(N). We study the continuum emission variation across the ALMA band 6 (i.e., spectral index) and compare the ALMA 1.3 mm continuum emission with previous SMA 345 GHz and VLA 40 GHz observations to study the nature of the sources detected. The brightest sources are dominated by (partially optically thick) dust emission, while there is an important degree of contamination from ionized gas free-free emission in weaker sources. While the total mass in SgrB2(M) is distributed in many fragments, most of the mass in SgrB2(N) arises from a single object, with filamentary-like structures converging toward the center. There seems to be a lack of low-mass dense cores in both regions. We determine H2 volume densities for the cores of about 107-109 cm-3 (or 105-107 Mʘ pc-3), i.e., one to two orders of magnitude higher than the stellar densities of super star clusters. We perform a statistical study of the chemical content of the identified sources. In general, SgrB2(N) is chemically richer than SgrB2(M). The chemically richest sources have about 100 lines per GHz and the fraction of luminosity contained in spectral lines at millimeter wavelengths with respect to the total luminosity is about 20%-40%. There seems to be a correlation between the chemical richness and the mass of the fragments, where more massive clumps are more chemically rich. Both SgrB2(N) and SgrB2(M) harbor a cluster of hot molecular cores. We compare the continuum images with predictions from a detailed 3D radiative transfer model that reproduces the structure of Sgr B2 from 45 pc down to 100 au. Conclusions. This ALMA dataset, together with other ongoing observational projects in the range 5 GHz to 200 GHz, better constrain the 3D structure of Sgr B2 and allow us to understand its physical and chemical structure. [ABSTRACT FROM AUTHOR]

The formation of high-mass stars is one of the major topics of astrophysical research, in particular the process of accretion from largescale clouds down to small-scale cores. We have selected the nearby, filamentary, high-mass star forming complex NGC6334 to study the gas velocity at different scales and probe the infall rates onto the protostellar cores embedded in the NGC6334-I and I(N) clusters. This study makes use of single-dish and interferometric submillimeter observations, complemented with 3D numerical non-LTE radiative transfer modeling. We measure a mass accretion rate of 10-5Mʘ yr-1 throughout the filament increasing up to 10-3Mʘ yr-1 towards the densest regions where high-mass stars are forming. At smaller scales, our 3D model is consistent with accretion rates of 10-3Mʘ yr-1 towards the clusters, and 10-4Mʘ yr-1 onto the protostars. [ABSTRACT FROM AUTHOR]

A review on current theories and observations of high-mass star formation is given. Particularly the influence of magnetic fields and feedback mechanisms, and of varying initial conditions on theories are discussed. The, in my biased view, most important observations to put strong constraints on models of high-mass star formation are presented, in particular bearing on the existence and properties of highmass starless cores, the role of filaments in the mass transport to highmass cores, and the properties of disks around high-mass stars. [ABSTRACT FROM AUTHOR]

Interstellar filaments pervade molecular clouds on all scales providing a bridge between the gas with relatively low densities and the dense clumps. In this work, we characterize various physical properties of filaments in the Orion A molecular cloud using preliminary datasets from the CARMA Orion project. We use an automated filament finding algorithm, DisPerSE, on 3D datacubes, and custom characterization algorithms. [ABSTRACT FROM AUTHOR]

We present results from radiative transfer modeling of the continuum emission towards Sagittarius B2 (hereafter Sgr B2). We have developed a radiative transfer framework - Pandora - that employs RADMC-3D (Dullemond 2012) for a self-consistent determination of the dust temperature. With this pipeline, we have set-up a single model that consistently reproduces the thermal dust and freefree continuum emission of Sgr B2 spanning four orders of magnitude in spatial scales (0.02-45 pc) and two orders of magnitude in frequency (20-4000 GHz). [ABSTRACT FROM AUTHOR]

Context. Hot molecular cores (HMCs) are intermediate stages of high-mass star formation and are also known for their rich chemical reservoirs and emission line spectra at (sub-)mm wavebands. Complex organic molecules (COMs) such as methanol (CH3OH), ethanol (C2H5OH), dimethyl ether (CH3OCH3), and methyl formate (HCOOCH3) produce most of these observed lines. The observed spectral feature of HMCs such as total number of emission lines and associated line intensities are also found to vary with evolutionary stages. Aims. We aim to investigate the spectral evolution of these COMs to explore the initial evolutionary stages of high-mass star formation including HMCs. Methods. We developed various 3D models for HMCs guided by the evolutionary scenarios proposed by recent empirical and modeling studies. We then investigated the spatio-temporal variation of temperature and molecular abundances in HMCs by consistently coupling gas-grain chemical evolution with radiative transfer calculations. We explored the effects of varying physical conditions on molecular abundances including density distribution and luminosity evolution of the central protostar(s) among other parameters. Finally, we simulated the synthetic spectra for these models at different evolutionary timescales to compare with observations. Results. Temperature has a profound effect on the formation of COMs through the depletion and diffusion on grain surface to desorption and further gas-phase processing. The time-dependent temperature structure of the hot core models provides a realistic framework for investigating the spatial variation of ice mantle evaporation as a function of evolutionary timescales. We find that a slightly higher value (15 K) than the canonical dark cloud temperature (10 K) provides a more productive environment for COM formation on grain surface. With increasing protostellar luminosity, the water ice evaporation font (~100 K) expands and the spatial distribution of gas phase abundances of these COMs also spreads out. We calculated the temporal variation of the radial profiles of these COMs for different hot core models. These profiles resemble the so-called jump profiles with relative abundances higher than 10-9 within the evaporation font will furthermore be useful to model the observed spectra of hot cores. We present the simulated spectra of these COMs for different hot core models at various evolutionary timescales. A qualitative comparison of the simulated and observed spectra suggests that these self-consistent hot core models can reproduce the notable trends in hot core spectral variation within the typical hot core timescales of 105 year. These models predict that the spatial distribution of various emission line maps will also expand with evolutionary time; this feature can be used to constrain the relative desorption energies of the molecules that mainly form on the grain surface and return to the gas phase via thermal desorption. The detailed modeling of the thermal structure of hot cores with similar masses along with the characterization of the desorption energies of different molecules can be used to constrain the luminosity evolution of the central protostars. The model predictions can be compared with high resolution observation that can probe scales of a few thousand AU in high-mass star forming regions such as from Atacama Large Millimeter/submillimeter Array (ALMA). We used a spectral fitting method to analyze the simulated spectra and find that it significantly underestimates some of the physical parameters such as temperature. The coupling of chemical evolution with radiative transfer models will be particularly useful to decipher the physical structure of hot cores and also to constrain the initial evolutionary stages of high-mass star formation. [ABSTRACT FROM AUTHOR]

Aims. We describe the assignment of a previously unidentified interstellar absorption line to ArH+ and discuss its relevance in the context of hydride absorption in diffuse gas with a low H2 fraction. The confidence of the assignment to ArH+ is discussed, and the column densities are determined toward several lines of sight. The results are then discussed in the framework of chemical models, with the aim of explaining the observed column densities. Methods. We fitted the spectral lines with multiple velocity components, and determined column densities from the line-to-continuum ratio. The column densities of ArH+ were compared to those of other species, tracing interstellar medium (ISM) components with different H2 abundances. We constructed chemical models that take UV radiation and cosmic ray ionization into account. Results. Thanks to the detection of two isotopologues, 36ArH+ and 38ArH+, we are confident about the carrier assignment to ArH+. NeH+ is not detected with a limit of [NeH+]/[ArH+] = 0.1. The derived column densities agree well with the predictions of chemical models. ArH+ is a unique tracer of gas with a fractional H2 abundance of 10-4 - 10-3 and shows little correlation to H2O+, which traces gas with a fractional H2 abundance of ˜0.1. Conclusions. A careful analysis of variations in the ArH+, OH+, H2O+, and HF column densities promises to be a faithful tracer of the distribution of the H2 fractional abundance by providing unique information on a poorly known phase in the cycle of interstellar matter and on its transition from atomic diffuse gas to dense molecular gas traced by CO emission. Abundances of these species put strong observational constraints upon magnetohydrodynamical (MHD)simulations of the interstellar medium, and potentially could evolve into a tool characterizing the ISM. Paradoxically, the ArH+ molecule is a better tracer of almost purely atomic hydrogen gas than Hi itself, since Hi can also be present in gas with a significant molecular content, but ArH+singles out gas that is >99.9% atomic. [ABSTRACT FROM AUTHOR]

We present new Herschel observations of the (6,6) and (9,9) inversion transitions of the hydronium ion toward Sagittarius B2(N) and W31C. Sensitive observations toward Sagittarius B2(N) show that the high, ∼500 K, rotational temperatures characterizing the population of the highly excited metastable H3O+ rotational levels are present over a wide range of velocities corresponding to the Sagittarius B2 envelope, as well as the foreground gas clouds between the Sun and the source. Observations of the same lines toward W31C, a line of sight that does not intersect the Central Molecular Zone but instead traces quiescent gas in the Galactic disk, also imply a high rotational temperature of ∼380 K, well in excess of the kinetic temperature of the diffuse Galactic interstellar medium. While it is plausible that some fraction of the molecular gas may be heated to such high temperatures in the active environment of the Galactic center, characterized by high X-ray and cosmic-ray fluxes, shocks, and high degree of turbulence, this is unlikely in the largely quiescent environment of the Galactic disk clouds. We suggest instead that the highly excited states of the hydronium ion are populated mainly by exoergic chemical formation processes and the temperature describing the rotational level population does not represent the physical temperature of the medium. The same arguments may be applicable to other symmetric top rotors, such as ammonia. This offers a simple explanation of the long-standing puzzle of the presence of a pervasive, hot molecular gas component in the central region of the Milky Way. Moreover, our observations suggest that this is a universal process not limited to the active environments associated with galactic nuclei. [ABSTRACT FROM AUTHOR]

Context. One of the big questions in astrochemistry is whether complex organic molecules are formed in the gas phase after evaporation of the icy mantles of interstellar dust grains or at intermediate temperatures within these icy mantles. Dimethyl ether (CH3OCH3) is one of these species that may form through either of these mechanisms, but it is yet unclear which is dominant. Aims. The goal of this paper is to determine the respective importance of solid state vs. gas phase reactions for the formation of dimethyl ether. This is done by a detailed analysis of the excitation properties of the ground state and the torsionally excited states, v11 = 1 and v15 = 1, toward the high-mass star-forming region G327.3-0.6. Methods. With the Atacama Pathfinder EXperiment 12 m submillimeter telescope, we performed a spectral line survey toward G327.3-0.6 around 1.3, 1.0, and 0.9 mm as well as at 0.43 and 0.37 mm. The observed CH3OCH3 spectrum is modeled assuming local thermal equilibrium. Results. CH3OCH3 has been detected in the ground state, v= 0, and in the torsionally excited states v11 = 1 and v15 = 1, for which lines have been detected here for the first time. The emission is modeled with an isothermal source structure as well as with a non-uniform spherical structure. In the isothermal case two components at 80 and 100 K are needed to reproduce the dimethyl ether emission, whereas an abundance jump at 85 K or a model with two abundance jumps at 70 and 100 K fit the emission equally well for the non-uniform source model. The emission from the torsionally excited states, v11 = 1 and v15 = 1, is very well fit by the same model as the ground state. Conclusions. For non-uniform source models one abundance jump for dimethyl ether is sufficient to fit the emission, but two components are needed for the isothermal models. This suggests that dimethyl ether is present in an extended region of the envelope and traces a non-uniform density and temperature structure. Both types of models furthermore suggest that most dimethyl ether is present in gas that is warmer than 100 K, but a smaller fraction of 5%-28% is present at temperatures between 70 and 100 K. The dimethyl ether present in this cooler gas is likely formed in the solid state, while gas phase formation probably is dominant above 100 K. Finally, the v11 = 1 and v15 = 1 torsionally excited states are easily excited under the density and temperature conditions in G327.3-0.6 and will thus very likely be detectable in other hot cores as well. [ABSTRACT FROM AUTHOR]

Context. One of the big questions in astrochemistry is whether complex organic molecules are formed in the gas phase after evaporation of the icy mantles of interstellar dust grains or at intermediate temperatures within these icy mantles. Dimethyl ether (CH3OCH3) is one of these species that may form through either of these mechanisms, but it is yet unclear which is dominant. Aims. The goal of this paper is to determine the respective importance of solid state vs. gas phase reactions for the formation of dimethyl ether. This is done by a detailed analysis of the excitation properties of the ground state and the torsionally excited states, ν11 = 1 and ν15 = 1, toward the high-mass star-forming region G327.3-0.6. Methods. With the Atacama Pathfinder EXperiment 12 m submillimeter telescope, we performed a spectral line survey toward G327.3-0.6 around 1.3, 1.0, and 0.9 mm as well as at 0.43 and 0.37 mm. The observed CH3OCH3 spectrum is modeled assuming local thermal equilibrium. Results. CH3OCH3 has been detected in the ground state, 3 = 0, and in the torsionally excited states ν11 = 1 and ν15 = 1, for which lines have been detected here for the first time. The emission is modeled with an isothermal source structure as well as with a non-uniform spherical structure. In the isothermal case two components at 80 and 100 K are needed to reproduce the dimethyl ether emission, whereas an abundance jump at 85 K or a model with two abundance jumps at 70 and 100 K fit the emission equally well for the non-uniform source model. The emission from the torsionally excited states, ν11 = 1 and ν15 = 1, is very well fit by the same model as the ground state. Conclusions. For non-uniform source models one abundance jump for dimethyl ether is sufficient to fit the emission, but two components are needed for the isothermal models. This suggests that dimethyl ether is present in an extended region of the envelope and traces a non-uniform density and temperature structure. Both types of models furthermore suggest that most dimethyl ether is present in gas that is warmer than 100 K, but a smaller fraction of 5%-28% is present at temperatures between 70 and 100 K. The dimethyl ether present in this cooler gas is likely formed in the solid state, while gas phase formation probably is dominant above 100 K. Finally, the ν11 = 1 and ν15 = 1 torsionally excited states are easily excited under the density and temperature conditions in G327.3-0.6 and will thus very likely be detectable in other hot cores as well. [ABSTRACT FROM AUTHOR]

Reports on homicides of adolescents in Fulton County, Georgia from 1988 to 1992. Sources of data; Statistics; Demographic information about the decedents; Geographic location of the crimes; Focus of prevention and intervention programs; Limitations of the study.

The role of massive (≥ 8 |$\, {\rm M}_{\odot }$|⁠) 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* ∼ 3 × 103 to 1 × 105 L⊙) sample of 38 massive star-forming regions observed with ALMA at 1.3 mm 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 and 15 per field). The flux density budget is split evenly (53 per cent–47 per cent) 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, λ 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 6.7 GHz 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 generalized approach used to distinguishing sources which are potentially star-forming from those which are not, utilizing interferometric visibility properties. [ABSTRACT FROM AUTHOR]

Aims. We aim to characterise certain physical properties of high-mass star-forming sites in the NGC6334 molecular cloud, such as the core mass function (CMF), spatial distribution of cores, and mass segregation. Methods. We used the Atacama Large Millimeter/sub-millimeter Array (ALMA) to image the embedded clusters NGC6334-I and NGC6334-I(N) in the continuum emission at 87.6 GHz. We achieved a spatial resolution of 1300 au, enough to resolve different compact cores and fragments, and to study the properties of the clusters. Results. We detected 142 compact sources distributed over the whole surveyed area. The ALMA compact sources are clustered in different regions. We used different machine-learning algorithms to identify four main clusters: NGC6334-I, NGC6334-I(N), NGC6334-I(NW), and NGC6334-E. The typical separations between cluster members range from 4000 au to 12 000 au. These separations, together with the core masses (0.1-100 M), are in agreement with the fragmentation being controlled by turbulence at scales of 0.1 pc. We find that the CMFs show an apparent excess of high-mass cores compared to the stellar initial mass function. We evaluated the effects of temperature and unresolved multiplicity on the derived slope of the CMF. Based on this, we conclude that the excess of high-mass cores might be spurious and due to inaccurate temperature determinations and/or resolution limitations. We searched for evidence of mass segregation in the clusters and we find that clusters NGC6334-I and NGC6334-I(N) show hints of segregation with the most massive cores located in the centre of the clusters. Conclusions. We searched for correlations between the physical properties of the four embedded clusters and their evolutionary stage (based on the presence of H II regions and infrared sources). NGC6334-E appears as the most evolved cluster, already harbouring a well-developed H II region. NGC6334-I is the second-most evolved cluster with an ultra-compact H II region. NGC6334-I(N) contains the largest population of dust cores distributed in two filamentary structures and no dominant H II region. Finally, NGC6334-I(NW) is a cluster of mainly low-mass dust cores with no clear signs of massive cores or H II regions. We find a larger separation between cluster members in the more evolved clusters favouring the role of gas expulsion and stellar ejection with evolution. The mass segregation, seen in the NGC6334-I and NGC6334-I(N) clusters, suggests a primordial origin for NGC6334-I(N). In contrast, the segregation in NGC6334-I might be due to dynamical effects. Finally, the lack of massive cores in the most evolved cluster suggests that the gas reservoir is already exhausted, while the less evolved clusters still have a large gas reservoir along with the presence of massive cores. In general, the fragmentation process of NGC6334 at large scales (from filament to clump, i.e. at about 1 pc) is likely governed by turbulent pressure, while at smaller scales (scale of cores and sub-fragments, i.e. a few hundred au) thermal pressure starts to be more significant. [ABSTRACT FROM AUTHOR]

Context. The G31.41+0.31 Unbiased ALMA sPectral Observational Survey (GUAPOS) project targets the hot molecular core (HMC) G31.41+0.31 (G31) to reveal the complex chemistry of one of the most chemically rich high-mass star-forming regions outside the Galactic center (GC). Aims. In the third paper of the project we present a study of nine O-bearing (CH3OH, 13CH3OH, CH318OH , CH3CHO, CH3OCH3, CH3COCH3, C2H5OH, aGg′-(CH2OH)2, and gGg′-(CH2OH)2) and six N-bearing (CH3CN,13CH3CN, CH313CN, C2H3CN, C2H5CN, and C2H513CN) complex organic molecules toward G31. The aim of this work is to characterize the abundances in G31 and to compare them with the values estimated in other sources. Moreover, we searched 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. In the discussion we also include the three isomers of C2H4O2 and the O- and N-bearing molecular species NH2CHO, CH3NCO, CH3C(O)CH2, and CH3NHCHO, which were analyzed in previous GUAPOS papers. Methods. Observations were carried out with the interferometer ALMA and cover the entire Band 3 from 84 to 116 GHz (~32 GHz bandwidth) with an angular resolution of 1.2″ × 1.2″ (~4400 au × 4400 au) and a spectral resolution of ~0.488 MHz (~1.3–1.7 km s−1). The transitions of the 14 molecular species were analyzed with the tool SLIM of MADCUBA to determine the physical parameters of the emitting gas. Moreover, we analyzed the morphology of the emission of the molecular species. Results. The values of abundances with respect to H2 in G31 range from 10−6 to 10−10 for the different species. We compared the abundances with respect to methanol of O-bearing, N-bearing, and O- and N-bearing COMs in G31 with 27 other sources, including other hot molecular cores inside and outside the GC, hot corinos, shocked regions, envelopes around young stellar objects, and quiescent molecular clouds, and with chemical models. Conclusions. From the comparison with other sources there is not a unique template for the abundances in hot molecular cores, pointing toward the importance of the thermal history for the chemistry of the various sources. The abundances derived from the chemical models are in good agreement, within a factor of 10, with those of G31. From the analysis of the maps we derived the peak positions of all the molecular species toward G31. 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. [ABSTRACT FROM AUTHOR]

Abstract. Observations of HDO are an important complement for studies of water, because they give strong constraints on the formation processes -- grain surfaces versus energetic process in the gas phase, e.g. in shocks. The HIFI observations of multiple transitions of HDO in Sgr B2(M) presented here allow the determination of the HDO abundance throughout the envelope, which has not been possible before with ground-based observations only. For more details, see Comito et al. (2010). [ABSTRACT FROM AUTHOR]

Hot molecular cores are a short-lived phase of massive star formation: the massive stars have heated up the dense molecular gas in which they are deeply embedded, but have not yet ionized and disrupted it. Information on their structure (density, temperature, velocity, molecular abundances) is needed both for research on massive star formation and for astrochemistry. We constrain their structure by radiative transfer modeling of a variety of molecular lines, including from highly excited states, using APEX and Herschel/HIFI. To spatially resolve the hot molecular gas, we performed VLA and SMA observations. In this article, we summarize some to the results. [ABSTRACT FROM AUTHOR]

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 (VLSR = [ − 3.5,   + 3.5] km s−1) with an angular extent of 0.95° ×1°, extending towards positive Galactic latitudes. The structure is offset from Sgr A* towards negative Galactic longitudes; it 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-m telescope towards 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. [ABSTRACT FROM AUTHOR]

The eXtended CASA Line Analysis Software Suite (XCLASS) is a toolbox for the Common Astronomy Software Applications package (CASA) containing new functions for modeling interferometric and single dish data. Among the tools is the myXCLASS program which calculates synthetic spectra by solving the radiative transfer equation for an isothermal object in one dimension, whereas the finite source size and dust attenuation are considered as well. Molecular data required by the myXCLASS program are taken from an embedded SQLite3 database containing entries from the Cologne Database for Molecular Spectroscopy (CDMS) and JPL using the Virtual Atomic and Molecular Data Center (VAMDC) portal. Additionally, the toolbox provides an interface for the model optimizer package Modeling and Analysis Generic Interface for eXternal numerical codes (MAGIX), which helps to find the best description of observational data using myXCLASS (or another external model program), that is, finding the parameter set that most closely reproduces the data. [ABSTRACT FROM AUTHOR]

We aim to fully describe the distribution and location of dense molecular clouds in the giant molecular cloud complex W43. It was previously identified as one of the most massive star-forming regions in our Galaxy. To trace the moderately dense molecular clouds in the W43 region, we initiated W43-HERO, a large program using the IRAM 30 m telescope, which covers a wide dynamic range of scales from 0.3 to 140 pc.We obtained on-the-fly-maps in 13CO (2-1) and C18O (2-1) with a high spectral resolution of 0.1 km s-1 and a spatial resolution of 12" . These maps cover an area of ~1.5 square degrees and include the two main clouds of W43 and the lower density gas surrounding them. A comparison to Galactic models and previous distance calculations confirms the location ofW43 near the tangential point of the Scutum arm at approximately 6 kpc from the Sun. The resulting intensity cubes of the observed region are separated into subcubes, which are centered on single clouds and then analyzed in detail. The optical depth, excitation temperature, and H2 column density maps are derived out of the 13CO and C18O data. These results are then compared to those derived from Herschel dust maps. The mass of a typical cloud is several 104 M☉ while the total mass in the dense molecular gas (>102 cm13) in W43 is found to be ~1.9×106 M☉. Probability distribution functions obtained from column density maps derived from molecular line data and Herschel imaging show a log-normal distribution for low column densities and a power-law tail for high densities. A flatter slope for the molecular line data probability distribution function may imply that those selectively show the gravitationally collapsing gas. [ABSTRACT FROM AUTHOR]

The building of online atomic and molecular databases for astrophysics and for other research fields started with the beginning of the internet. These databases have encompassed different forms: databases of individual research groups exposing their own data, databases providing collected data from the refereed literature, databases providing evaluated compilations, databases providing repositories for individuals to deposit their data, and so on. They were, and are, the replacement for literature compilations with the goal of providing more complete and in particular easily accessible data services to the users communities. Such initiatives involve not only scientific work on the data, but also the characterization of data, which comes with the "standardization" of metadata and of the relations between metadata, as recently developed in different communities. This contribution aims at providing a representative overview of the atomic and molecular databases ecosystem, which is available to the astrophysical community and addresses different issues linked to the use and management of data and databases. The information provided in this paper is related to the keynote lecture "Atomic and Molecular Databases: Open Science for better science and a sustainable world" whose slides can be found at DOI : doi.org/10.5281/zenodo.6979352 on the Zenodo repository connected to the "cb5-labastro" Zenodo Community (https://zenodo.org/communities/cb5-labastro). [ABSTRACT FROM AUTHOR]

Context. The formation process of high-mass stars (>8 M⊙) is poorly constrained, particularly the effects of clump fragmentation creating multiple systems and the mechanism of mass accretion onto the cores. Aims. We study the fragmentation of dense gas clumps, and trace the circumstellar rotation and outflows by analyzing observations of the high-mass (~500 M⊙) star-forming region IRAS 23033+5951. Methods. Using the Northern Extended Millimeter Array (NOEMA) in three configurations and the IRAM 30 m single-dish telescope at 220 GHz, we probe the gas and dust emission at an angular resolution of ~0.45′′, corresponding to 1900 au. Results. In the millimeter (mm) continuum emission, we identify a protostellar cluster with at least four mm-sources, where three of them show a significantly higher peak intensity well above a signal-to-noise ratio of 100. Hierarchical fragmentation from large to small spatial scales is discussed. Two fragments are embedded in rotating structures and drive molecular outflows, traced by 13CO (2–1) emission. The velocity profiles across two of the cores are similar to Keplerian but are missing the highest-velocity components close to the center of rotation, which is a common phenomena from observations like these, and other rotation scenarios are not excluded entirely. Position–velocity diagrams suggest protostellar masses of ~6 and 19 M⊙. Rotational temperatures from fitting CH3CN (12K− 11K) spectra are used for estimating the gas temperature and thereby also the disk stability against gravitational fragmentation, utilizing Toomre's Q parameter. Assuming that the candidate disk is in Keplerian rotation about the central stellar object and considering different disk inclination angles, we identify only one candidate disk as being unstable against gravitational instability caused by axisymmetric perturbations. Conclusions. The dominant sources cover different evolutionary stages within the same maternal gas clump. The appearance of rotation and outflows of the cores are similar to those found in low-mass star-forming regions. [ABSTRACT FROM AUTHOR]

CCAT is a 25 meter submm telescope proposed to be built at 5600 meters elevation on Cerro Chajnantor overlooking the ALMA site in northern Chile. The CCAT site is the best submm site that is accessible by truck, so that with its large aperture, exceptionally good surface accuracy (~17 µm rms total wavefront error, WFE), state-of-theart instrumentation and large (≥20 arcmin) field-of-view (FoV) CCAT will deliver unsurpassed point source sensitivity and mapping speeds across the submm telluric windows. Our primary science goals are: (1) to trace the obscurred star formation (SF) history of the Universe through multicolor submm surveys of 100's deg² on the sky followed up by spectroscopy to characterize the energy sources in dusty SF galaxies; (2) to measure and characterize the SF process in the Milky Way galaxy and nearby resolved galaxies through submm spectroscopic and dust continuum surveys; and (3) to probe galaxy cluster astrophysics through the Sunyaev-Zeldovich (SZ) effect. [ABSTRACT FROM AUTHOR]

We have observed five sulphur-bearing molecules in foreground diffuse molecular clouds lying along the sight-lines to five bright continuum sources. We have used the GREAT instrument on SOFIA to observe the SH 1383 GHz 2Π3/2 ← = 5/2 = 3/2 lambda doublet toward the star-forming regions W31C, G29.96-0.02, G34.3+0.1, W49N and W51, detecting foreground absorption towards all five sources; and the EMIR receivers on the IRAM 30 m telescope at Pico Veleta to detect the H2S 110-101 (169 GHz), CS J = 2-1 (98 GHz) and SO 32-21 (99 GHz) transitions. Upper limits on the H3S+ 10-00 (293 GHz) transition were also obtained at the IRAM 30 m. In nine foreground absorption components detected towards these sources, the inferred column densities of the four detected molecules showed relatively constant ratios, with N(SH)/N(H2S) in the range 1.1-3.0, N(CS)/N(H2S) in the range 0.32-0.61, and N(SO)/N(H2S) in the range 0.08-0.30. The column densities of the sulphur-bearing molecules are very well correlated amongst themselves, moderately well correlated with CH (a surrogate tracer for H2), and poorly correlated with atomic hydrogen. The observed SH/H2 ratios - in the range 5 to 26 × 10-9 - indicate that SH (and other sulphur-bearing molecules) account for «1% of the gas-phase sulphur nuclei. The observed abundances of sulphur-bearing molecules, however, greatly exceed those predicted by standard models of cold diffuse molecular clouds, providing further evidence for the enhancement of endothermic reaction rates by elevated temperatures or ion-neutral drift. We have considered the observed abundance ratios in the context of shock and turbulent dissipation region (TDR) models. Using the TDR model, we find that the turbulent energy available at large scale in the diffuse ISM is sufficient to explain the observed column densities of SH and CS. Standard shock and TDR models, however, fail to reproduce the column densities of H2S and SO by a factor of about 10; more elaborate shock models - in which account is taken of the velocity drift, relative to H2, of SH molecules produced by the dissociative recombination of H3S+ - reduce this discrepancy to a factor ~3. [ABSTRACT FROM AUTHOR]

Context. How molecular clouds form out of the atomic phase and what the relative fractions of carbon are in the ionized, atomic, and molecular phase are questions at the heart of cloud and star formation. Aims. We want to understand the kinematic processes of gas flows during the formation of molecular clouds. In addition to that, we aim at determining the abundance ratios of carbon in its various gas phases from the ionized to the molecular form. Methods. Using multiple observatories from Herschel and SOFIA to APEX and the IRAM 30m telescope, we mapped the ionized and atomic carbon as well as carbon monoxide ([CII] at 1900 GHz, [CI] at 492 GHz, and C18O(2-1) at 220 GHz) at high spatial resolution (12"-25") in four young massive infrared dark clouds (IRDCs). Results. The three carbon phases were successfully mapped in all four regions, only in one source does the [CII] line remain a nondetection. With these data, we dissect the spatial and kinematic structure of the four IRDCs and determine the abundances of gas phase carbon in its ionized, atomic, and most abundant molecular form (CO). Both the molecular and atomic phases trace the dense structures well, with [CI] also tracing material at lower column densities. [CII] exhibits diverse morphologies in our sample from compact to diffuse structures, probing the cloud environment. In at least two out of the four regions, we find kinematic signatures strongly indicating that the dense gas filaments have formed out of a dynamically active and turbulent atomic and molecular cloud, potentially from converging gas flows. The atomic carbon-to-CO gas mass ratios are low between 7% and 12% with the lowest values found toward the most quiescent region. In the three regions where [CII] is detected, its mass is always higher by a factor of a few than that of the atomic carbon. While the ionized carbon emission depends on the radiation field, we also find additional signatures that indicate that other processes, for example, energetic gas flows can contribute to the [CII] excitation as well. Conclusions. Combining high-resolution maps in the different carbon phases reveals the dynamic interplay of the various phases of the interstellar medium during cloud formation. Extending these studies to more evolved stages and combining the observations with molecular cloud formation simulations including the chemistry and radiative transfer will significantly improve our understanding of the general interstellar medium, cloud, and star formation processes. [ABSTRACT FROM AUTHOR]

Context. Numerical simulations have explored the possibility of forming molecular clouds through either a quasi-static, selfgravitating mechanism or the collision of gas streams or lower density clouds. They also quantitatively predict the distribution of matter at the transition from atomic to molecular gases. Aims. We aim to observationally test these models by studying the environment of W43, a molecular cloud complex recently identified near the tip of the Galactic long bar. Methods. Using Galaxy-wide Hi and 12CO 1-0 surveys, we searched for gas flowing toward the W43 molecular cloud complex. We also estimated the Hi and H2 mass surface densities to constrain the transition from atomic to molecular gas around and within W43. Results. We found three cloud ensembles within the position-velocity diagrams of 12CO and Hi gases. They are separated by ~20 km s-1 along the line of sight and extend into the 13CO velocity structure of W43. Since their velocity gradients are consistent with free fall, they could be nearby clouds attracted by and streaming toward the W43 ~107 M☉ potential well. We show that the Hi surface density, ΣHI = 45-85 M☉ pc-2, does not reach any threshold level but increases when entering the 130 pc-wide molecular complex previously defined. This suggests that an equilibrium between H2 formation and photodissociation has not yet been reached. The H2-to-H I ratio measured over the W43 region and its surroundings, RH2 ~ 3.5±32 , is high, indicating that most of the gas is already in molecular form in W43 and in structures several hundred parsecs downstream along the Scutum-Centaurus arm. Conclusions. The W43 molecular cloud complex may have formed and, in fact may still be accreting mass from the agglomeration of clouds. Already in the molecular-dominated regime, most of these clouds are streaming from the Scutum-Centaurus arm. This clearly disagrees with quasi-static and steady-state models of molecular cloud formation. [ABSTRACT FROM AUTHOR]

Context. Star formation effciency (SFE) theories are currently based on statistical distributions of turbulent cloud structures and a simple model of star formation from cores. They remain poorly tested, especially at the highest densities. Aims. We investigate the effects of gas density on the SFE through measurements of the core formation effciency (CFE). With a total mass of ∼2 × 104 M☉ the W43-MM1 ridge is one of the most convincing candidate precursors of Galactic starburst clusters and thus one of the best places to investigate star formation. Methods. We used high-angular resolution maps obtained at 3 mm and 1 mm within the W43-MM1 ridge with the IRAM Plateau de Bure Interferometer to reveal a cluster of 11 massive dense cores, and, one of the most massive protostellar cores known. A Herschel column density image provided the mass distribution of the cloud gas. We then measured the "instantaneous" CFE and estimated the SFE and the star formation rate (SFR) within subregions of the W43-MM1 ridge. Results. The high SFE found in the ridge (∼6% enclosed in ∼8 pc3) confirms its ability to form a starburst cluster. There is, however, a clear lack of dense cores in the eastern part of the ridge, which may be currently assembling. The CFE and the SFE are observed to increase with volume gas density, while the SFR per free fall time steeply decreases with the virial parameter, αvir. Statistical models of the SFR may describe the outskirts of the W43-MM1 ridge well, but struggle to reproduce its inner part, which corresponds to measurements at low αvir. It may be that ridges do not follow the log-normal density distribution, Larson relations, and stationary conditions forced in the statistical SFR models. [ABSTRACT FROM AUTHOR]

We investigate the physical and chemical processes at work during the formation of a massive protostar based on the observation of water in an outflow from a very young object previously detected in H2 and SiO in the IRAS 17233-3606 region. We estimated the abundance of water to understand its chemistry, and to constrain the mass of the emitting outflow. We present new observations of shocked water obtained with the HIFI receiver onboard Herschel. We detected water at high velocities in a range similar to SiO. We self-consistently fitted these observations along with previous SiO data through a state-of-the-art, one-dimensional, stationary C-shock model. We found that a single model can explain the SiO and H2O emission in the red and blue wings of the spectra. Remarkably, one common area, similar to that found for H2 emission, fits both the SiO and H2O emission regions. This shock model subsequently allowed us to assess the shocked water column density, NH2O = 1.2 × 1018 cm-2, mass, MH2O = 12.5 M⊕, and its maximum fractional abundance with respect to the total density, xH2O = 1.4 × 10-4. The corresponding water abundance in fractional column density units ranges between 2.5×10-5 and 1.2×10-5, in agreement with recent results obtained in outflows from low- and high-mass young stellar objects. [ABSTRACT FROM AUTHOR]

Context. The discovery of amino acids in meteorites fallen to Earth and the detection of glycine, the simplest of them, in samples returned from a comet to Earth strongly suggest that the chemistry of the interstellar medium is capable of producing such complex organic molecules and that they may be widespread in our Galaxy. Aims. Our goal is to investigate the degree of chemical complexity that can be reached in the interstellar medium, in particular in dense star-forming regions. Methods. We performed an unbiased, spectral line survey toward Sgr B2(N) and (M), two regions where high-mass stars are formed, with the IRAM 30 m telescope in the 3 mm atmospheric transmission window. Partial surveys at 2 and 1.3 mm were performed in parallel. The spectra were analyzed with a simple radiative transfer model that assumes local thermodynamic equilibrium but takes optical depth effects into account. Results. About 3675 and 945 spectral lines with a peak signal-to-noise ratio higher than 4 are detected at 3 mm toward Sgr B2(N) and (M), i.e. about 102 and 26 lines per GHz, respectively. This represents an increase by about a factor of two over previous surveys of Sgr B2. About 70% and 47% of the lines detected toward Sgr B2(N) and (M) are identified and assigned to 56 and 46 distinct molecules as well as to 66 and 54 less abundant isotopologues of these molecules, respectively. In addition, we report the detection of transitions from 59 and 24 catalog entries corresponding to vibrationally or torsionally excited states of some of these molecules, respectively, up to a vibration energy of 1400 cm-1 (2000 K). Excitation temperatures and column densities were derived for each species but should be used with caution. The rotation temperatures of the detected complex molecules typically range from ~50 to 200 K. Among the detected molecules, aminoacetonitrile, n-propyl cyanide, and ethyl formate were reported for the first time in space based on this survey, as were five rare isotopologues of vinyl cyanide, cyanoacetylene, and hydrogen cyanide. We also report the detection of transitions from within twelve new vibrationally or torsionally excited states of known molecules. Absorption features produced by diffuse clouds along the line of sight are detected in transitions with low rotation quantum numbers of many simple molecules and are modeled with ~30-40 velocity components with typical linewidths of ~3-5 km s-1. Conclusions. Although the large number of unidentified lines may still allow future identification of new molecules, we expect most of these lines to belong to vibrationally or torsionally excited states or to rare isotopologues of known molecules for which spectroscopic predictions are currently missing. Significant progress in extending the inventory of complex organic molecules in Sgr B2(N) and deriving tighter constraints on their location, origin, and abundance is expected in the near future thanks to an ongoing spectral line survey at 3 mm with ALMA in its cycles 0 and 1. The present single-dish survey will serve as a solid basis for the line identification and analysis of such an interferometric survey. [ABSTRACT FROM AUTHOR]

The formation of high-mass stars is tightly linked to that of their parental clouds. Here, we focus on the high-density parts of W43, a molecular cloud undergoing an efficient event of star formation. Using a column density image derived from Herschel continuum maps, we identify two high-density filamentary clouds, called the W43-MM1 and W43-MM2 ridges. Both have gas masses of 2.1 × 104M☼ and 3.5 × 104M☼ above >10 and within areas of ∼6 and ∼14 pc2, respectively. The W43-MM1 and W43-MM2 ridges are structures that are coherent in velocity and gravitationally bound, despite their large velocity dispersion measured by the N2H+ (1-0) lines of the W43-HERO IRAM large program. Another intriguing result is that these ridges harbor widespread (∼10 pc2) bright SiO (2-1) emission, which we interpret to be the result of low-velocity shocks (⩽10 km s–1). We measure a significant relationship between the SiO (2-1) luminosity and velocity extent and show that it distinguishes our observations from the high-velocity shocks associated with outflows. We use state-of-the-art shock models to demonstrate that a small percentage (10%) of Si atoms in low-velocity shocks, observed initially in gas phase or in grain mantles, can explain the observed SiO column density in the W43 ridges. The spatial and velocity overlaps between the ridges of high-density gas and the shocked SiO gas suggest that ridges could be forming via colliding flows driven by gravity and accompanied by low-velocity shocks. This mechanism may be the initial conditions for the formation of young massive clusters. [ABSTRACT FROM AUTHOR]

Context. The APEX Telescope Large Area Survey of the GALaxy (ATLASGAL) is the first systematic survey of the inner Galactic plane in the sub-millimetre. The observations were carried out with the Large APEX Bolometer Camera (LABOCA), an array of 295 bolometers observing at 870 μm (345 GHz). Aims. Here we present a first version of the compact source catalogue extracted from this survey. This catalogue provides an unbiased database of dusty clumps in the inner Galaxy. Methods. The construction of this catalogue was made using the source extraction routine SExtractor. We have cross-associated the obtained sources with the IRAS and MSX catalogues, in order to constrain their nature. Results. We have detected 6639 compact sources in the range from 330 ≤ ℓ ≤ 21 degrees and ∣b∣ ≤ 1.5 degrees. The catalogue has a 99% completeness for sources with a peak flux above 6σ, which corresponds to a flux density of ∼0.4 Jy beam-1. The parameters extracted for sources with peak fluxes below the 6σ completeness threshold should be used with caution. Tests on simulated data find the uncertainty in the flux measurement to be ∼12%, however, in more complex regions the flux values can be overestimated by a factor of 2 due to the additional background emission. Using a search radius of 30″ we found that 40% of ATLASGAL compact sources are associated with an IRAS or MSX point source, but, ∼50% are found to be associated with MSX 21 μm fluxes above the local background level, which is probably a lower limit to the actual number of sources associated with star formation. Conclusions. Although infrared emission is found towards the majority of the clumps detected, this catalogue is still likely to include a significant number of clumps that are devoid of star formation activity and therefore excellent candidates for objects in the coldest, earliest stages of (high-mass) star formation. [ABSTRACT FROM AUTHOR]

The Modeling and Analysis Generic Interface for eXternal numerical codes (MAGIX) is a model optimizer developed under the framework of the coherent set of astrophysical tools for spectroscopy (CATS) project. The MAGIX package provides a framework of an easy interface between existing codes and an iterating engine that attempts to minimize deviations of the model results from available observational data, constraining the values of the model parameters and providing corresponding error estimates. Many models (and, in principle, not only astrophysical models) can be plugged into MAGIX to explore their parameter space and find the set of parameter values that best fits observational/experimental data. MAGIX complies with the data structures and reduction tools of Atacama Large Millimeter Array (ALMA), but can be used with other astronomical and with non-astronomical data. [ABSTRACT FROM AUTHOR]

The ATLASGAL 870 μm continuum survey conducted with the APEX telescope is the first one covering the whole inner Galactic plane (60° > l > -60° and b < ±1.°5) in submillimeter (submm) continuum emission tracing the cold dust of dense and young star-forming regions. Here, we present the overall distribution of sources within our Galactic disk. The submm continuum emission is confined to a narrow range around the Galactic plane, but shifted on average by ~0.07 deg below the plane. Source number counts show strong enhancements toward the Galactic center, the spiral arms, and toward prominent star-forming regions. Comparing the distribution of ATLASGAL dust continuum emission to that of young intermediate- to high-mass young stellar objects (YSOs) derived from Spitzer data, we find similarities as well as differences. In particular, the distribution of submm dust continuum emission is significantly more confined to the plane than the YSO distribution (FWHM of 0.7 and 1.1 deg, corresponding to mean physical scale heights of approximately 46 and 80 pc, respectively). While this difference may partly be caused by the large extinction from the dense submm cores, gradual dispersal of stellar distributions after their birth could also contribute to this effect. Compared to other tracers of Galactic structure, the ATLASGAL data are strongly confined to a narrow latitude strip around the Galactic plane. [ABSTRACT FROM AUTHOR]

ABSTRACT We have mapped 20 spectral lines in the Central Molecular Zone (CMZ) around the Galactic Centre, emitting from 85.3 to 93.3 GHz. This work used the 22-m Mopra radio telescope in Australia, equipped with the 8-GHz bandwidth University of New South Wales-Mopra Spectrometer (UNSW-MOPS) digital filter bank, obtaining ∼2 km s−1 spectral and ∼40 arcsec spatial resolution. The lines measured include emission from the c-C3H2, CH3CCH, HOCO+, SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+ molecules. The area covered is Galactic longitude −07 to 18 and latitude −03 to 02, including the bright dust cores around Sgr A, Sgr B2, Sgr C and G1.6−0.025. We present images from this study and conduct a principal component analysis on the integrated emission from the brightest eight lines. This is dominated by the first component, showing that the large-scale distribution of all molecules is very similar. We examine the line ratios and optical depths in selected apertures around the bright dust cores, as well as for the complete mapped region of the CMZ. We highlight the behaviour of the bright HCN, HNC and HCO+ line emission, together with that from the 13C isotopologues of these species, and compare the behaviour with that found in extragalactic sources where the emission is unresolved spatially. We also find that the isotopologue line ratios (e.g. HCO+/H13CO+) rise significantly with increasing redshifted velocity in some locations. Line luminosities are also calculated and compared to that of CO, as well as to line luminosities determined for external galaxies. [ABSTRACT FROM AUTHOR]

The large number of high-J lines of C18O available via the Herschel Space Observatory provide an unprecedented ability to model the total CO column density in hot cores. Using the emission from all the observed lines (up to J = 15-14), we sum the column densities in each individual level to obtain the total column alter correcting for the population in the unobserved states. With additional knowledge of source size, VLSR, and line width, and both local thermodynamic equilibrium (LTE) and non-LTE modeling, we have determined the total C18O column densities in the Extended Ridge, Outflow/Plateau, Compact Ridge, and Hot Core components of Orion KL to be 1.4 x 1016 cm-2, 3.5 x 1016 cm-2 2.2 x 1016 cm-2, and 6.2 x 1016, respectively. We also find that the C18O/C17O abundance ratio varies from 1.7 in the Outflow/Plateau, 2.3 in the Extended Ridge, 3.0 in the Hot Core, and to 4.1 in the Compact Ridge. This is in agreement with models in which regions with higher ultraviolet radiation fields selectively dissociate C17O, although care must be taken when interpreting these numbers due to the size of the uncertainties in the C18O/C17O abundance ratio. [ABSTRACT FROM AUTHOR]

Using the Mopra telescope, we have undertaken a 3-mm spectral-line imaging survey of a 5 × 5 arcmin2 area around Sgr B2. We covered almost the complete spectral range from 81.7 to 113.5 GHz, with 2.2 MHz wide spectral channels or and have observed 24 lines, with 0.033 MHz wide, or channels. We discuss the distribution of around 50 lines, and present velocity-integrated emission images for 38 of the lines. In addition, we have detected around 120 more lines, mostly concentrated at the particularly spectral-line-rich Sgr B2(N) source. There are significant differences in molecular emission, pointing to both abundance and excitation differences throughout the region. Seven distinct spatial locations are identified for the emitting species, including peaks near the prominent star-forming cores of Sgr B2(N), (M) and (S) that are seen in infrared (IR)-to-radio continuum images. The other features are a ‘north ridge’ and a ‘north cloud’ to the north of the Sgr B2 N-M-S cores, a ‘south-east peak’ and a ‘west ridge’. The column density, as evident through C18O, peaks at the Sgr B2(N) and (M) cores, where strong absorption is also evident in otherwise generally bright lines such as HCO+, HCN and HNC. Most molecules trace a ridge line to the west of the Sgr B2 N-M-S cores, wrapping around the cores and extending north-east to the north cloud. This is most clearly evident in the species HC3N, CH3CN, CH3OH and OCS. They are found to be closer in distribution to the cooler dust traced by the submillimetre continuum than either the warmer dust seen in the mid-IR or to the radio continuum. The molecule CN, in contrast, is reasonably uniform over the entire region mapped, aside from strong absorption at the positions of the Sgr B2(N) and (M) cores. [ABSTRACT FROM AUTHOR]

The APEX-SZ experiment is a sky survey designed to discover galaxy clusters via the Sunyaev–Zel’dovich effect at millimeter wavelengths. We describe the components of the instrument, including the 12 m Atacama Pathfinder Experiment telescope, optics, Transition-edge sensor bolometer array and SQUID readout. APEX-SZ will begin observations in 2004. [Copyright &y& Elsevier]

In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH+, H2O+, and H3O+ begins with the ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H2. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray ionization rate of atomic hydrogen (ζH) and molecular hydrogen fraction (). We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines. From the molecular abundances we compute in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042 ± 0.018. This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H2 fractions. We also infer ζH throughout our sample, and find a lognormal distribution with mean log (ζH) = –15.75 (ζH = 1.78 × 10–16 s–1) and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray ionization rates previously inferred from H observations. Ionization rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies. [ABSTRACT FROM AUTHOR]

A correction to the article "Complex Organic Molecules in the Interstellar Medium: IRAM 30 m Line Survey of Sagittarius B2(N) and (M)" published in a previous issue of the journal is presented.