Atacama Pathfinder Experiment Research Articles

The effects of stellar feedback on molecular clumps in the Lagoon Nebula (M8)

The Lagoon Nebula (M8) is host to multiple regions with recent and ongoing massive star formation, due to which it appears as one of the brightest regions in the sky. M8-Main and M8 East, two prominent regions of massive star formation, have been studied in detail over the past few years, while large parts of the nebula and its surroundings have received little attention. These largely unexplored regions comprise a large sample of molecular clumps that are affected by the presence of massive O- and B-type stars. Thus, exploring the dynamics and chemical composition of these clumps will improve our understanding of the feedback from massive stars on star-forming regions in their vicinity. We established an inventory of species observed towards 37 known molecular clumps in M8 and investigated their physical structure. We compared our findings for these clumps with the galaxy-wide sample of massive dense clumps observed as part of the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). Furthermore, we investigated the region for signs of star formation and stellar feedback. To obtain an overview of the kinematics and chemical abundances across the sample of molecular clumps in the M8 region, we conducted an unbiased line survey for each clump. We used the Atacama Pathfinder EXperiment (APEX) 12\,m submillimetre telescope and the 30m telescope of the Institut de Radioastronomie e trique (IRAM) to conduct pointed on-off observations of 37 clumps in M8. These observations cover bandwidths of 53\,GHz and 40\,GHz in frequency ranges from 210\,GHz to 280\,GHz and from 70\,GHz to 117\,GHz, respectively. Temperatures were derived from rotational transitions of acetonitrile, methyl acetylene, and para-formaldehyde. Additional archival data from the Spitzer Herschel MSX, APEX, WISE, JCMT, and AKARI telescopes were used to investigate the morphology of the region and to derive the physical parameters of the dust emission by fitting spectral energy distributions to the observed flux densities. Across the observed M8 region, we identify 346 transitions from 70 different molecular species, including isotopologues. While many species and fainter transitions are detected exclusively towards M8 East, we also observe a large chemical variety in many other molecular clumps. We detect tracers of photo-dissociation regions (PDRs) across all the clumps, and 38<!PCT!> of these clumps show signs of star formation. In our sample of clumps with extinctions between 1 and 60\,mag, we find that PDR tracers are most abundant in clumps with relatively low H$_2$ column densities. When comparing M8 clumps to ATLASGAL sources at similar distances, we find them to be slightly less massive (median $10\ M_ odot $) and have compatible luminosities (median $200\ L_ odot $) and radii (median $0.16$\,pc). In contrast, dust temperatures of the clumps in M8 are found to be increased by approximately 5\,K (25<!PCT!>), indicating substantial external heating of the clumps by radiation of the present O- and B-type stars. This work finds clear and widespread effects of stellar feedback on the molecular clumps in the Lagoon Nebula. While the radiation from the O- and B-type stars possibly causes fragmentation of the remnant gas and heats the molecular clumps externally, it also gives rise to extended PDRs on the clump surfaces. Despite this fragmentation, the dense cores within 38<!PCT!> of the observed clumps in M8 are forming a new generation of stars.

Exploring Molecular Gas toward the Magellanic Bridge

The Magellanic Bridge (MB) is a diffuse gas structure that connects the Large Magellanic Cloud with the Small Magellanic Cloud. The MB is the closest tidal interaction system between two galaxies to the Milky Way. Taking into account that young stellar objects are embedded in such gaseous structure, it is a unique laboratory to investigate gas dynamics and star formation processes in a very low metallicity environment. In this work we present a preview of the results obtained from observations made with the Atacama Pathfinder Experiment telescope toward some regions of the MB. Through the emission of the 12CO J = 2–1 line we characterize the molecular gas of these regions.

A possible relation between global CO excitation and massive molecular outflows in local ULIRGs

Local ultra-luminous infrared galaxies (ULIRGs) have been observed to host ubiquitous molecular outflows, including the most massive and powerful ever detected. These sources have also exceptionally excited global, galaxy-integrated CO ladders. A connection between outflows and molecular gas excitation has however never been established, since previous multi-$J$ CO surveys were limited in spectral resolution and sensitivity and so they could only probe the global molecular gas conditions. In this work, we address this question using new, ground-based, sensitive heterodyne spectroscopy of multiple CO rotational lines (up to CO(7--6)) in a sample of 17 local ULIRGs. We used the Atacama Pathfinder Experiment (APEX) telescope to survey the CO($J_ up lines at a high signal-to-noise ratio, and complemented these data with up APEX and Atacama Large Millimeter Array (ALMA and ACA) observations presented in Montoya Arroyave et al. (2023). We detected a total of 74 (out of 75) CO lines, with up to six transitions per source. The resulting CO spectral line energy distributions (SLEDs) show a wide range in gas excitation, in agreement with previous studies on ULIRGs. Some CO SLEDs peak at up which we classify as ``lower excitation'', while others plateau or keep increasing up to the highest-$J$ CO transition probed, and we classify these as ``higher excitation''. Our analysis includes for completeness the results of CO SLED fits performed with a single large velocity gradient component, but our main focus is the investigation of possible links between global CO excitation and the presence of broad and/or high-velocity CO spectral components that can contain outflowing gas. We discovered an increasing trend of line width as a function of up $ of the CO transition, which is significant at the $4 level and appears to be driven by the eight sources that we classified as higher excitation. We further analyzed such higher-excitation ULIRGs, by performing a decomposition of their CO spectral profiles into multiple components and we derived CO ladders that are clearly more excited for the spectral components characterized by higher velocities and/or velocity dispersion. Because these sources are known to host widespread molecular outflows, we favor an interpretation whereby the highly excited CO-emitting gas in ULIRGs resides in galactic-scale massive molecular outflows whose emission fills a large fraction of the beam of our APEX high-$J$ CO observations. On the other hand, our results challenge alternative scenarios for which the high CO excitation in ULIRGs can be explained by classical component of the interstellar medium, such as photon- or X-ray dominated regions around the nuclear sources

Nuclear spin ratios of deuterated ammonia in prestellar cores LAsMA observations of H-MM1 and Oph D

Context. Molecules containing two or more hydrogen or deuterium atoms have different nuclear spin states which behave as separate chemical species. The relative abundances of these species can give clues to their origin. Formation on grains is believed to yield statistical spin ratios whereas gas-phase reactions are predicted to result in clear deviations from them. This is also true for ammonia and its deuterated forms NH2D, NHD2, and ND3. Aims. Here we aim to determine the ortho/para ratios of NH2D and NHD2 in dense, starless cores, where their formation is supposed to be dominated by gas-phase reactions. Methods. The Large APEX sub-Millimeter Array (LAsMA) multibeam receiver of the Atacama Pathfinder EXperiment (APEX) telescope was used to observe the prestellar cores H-MM1 and Oph D in Ophiuchus in the ground-state lines of ortho and para NH2D and NHD2. The fractional abundances of these molecules were derived employing three-dimensional radiative transfer modelling, using different assumptions about the abundance profiles as functions of density. We also ran gas-grain chemistry models with different scenarios concerning proton or deuteron exchanges and chemical desorption from grains to find out if one of these models can reproduce the observed spin ratios. Results. The observationally deduced ortho/para ratios of NH2D and NHD2 are in both cores within 10% of their statistical values 3 and 2, respectively, and taking 3 σ limits, deviations from these of about 20% are allowed. Of the chemistry models tested here, the model that assumes proton hop (as opposed to full scrambling) in reactions contributing to ammonia formation, and a constant efficiency of chemical desorption, comes nearest to the observed abundances and spin ratios. Conclusions. The nuclear spin ratios derived here are in contrast with spin-state chemistry models that assume full scrambling in proton donation and hydrogen abstraction reactions leading to deuterated ammonia. The efficiency of chemical desorption strongly influences the predicted abundances of NH3, NH2D, and NHD2, but has a lesser effect on their ortho/para ratios. For these the proton exchange scenario in the gas is decisive. We suggest that this is because of rapid re-processing of ammonia and related cations by gas-phase ion-molecule reactions.

CONCERTO: Instrument and status

CONCERTO (CarbON CII line in post-rEionization and ReionizaTiOn) is a low-resolution Fourier transform spectrometer dedicated to the study of star-forming galaxies and clusters of galaxies in the transparent millimeter windows from the ground. It is characterized by a wide instantaneous 18.6 arcmin field of view, operates at 130–310 GHz, and was installed on the 12-meter Atacama Pathfinder Experiment (APEX) telescope at 5 100m above sea level. CONCERTO’s double focal planes host two arrays of 2 152 kinetic inductance detectors and represent a pioneering instrument to meet a state-of-the-art scientific challenge. This paper introduces the CONCERTO instrument and explains its status, shows the first CONCERTO spectral maps of Orion, and describes the perspectives of the project.

The first ground-based detection of the 752 GHz water line in local ultra-luminous infrared galaxies using APEX-SEPIA

Abstract We report the first ground-based detection of the water line p-H2O (211–202) at 752.033 GHz in three z < 0.08 ultra-luminous infrared galaxies (ULIRGs): IRAS 06035-7102, IRAS 17207-0014 and IRAS 09022-3615. Using the Atacama Pathfinder EXperiment (APEX), with its Swedish-ESO PI Instrument for APEX (SEPIA) band-9 receiver, we detect this H2O  line with overall signal-to-noise ratios of 8–10 in all three galaxies. Notably, this is the first detection of this line in IRAS 06035-7102. Our new APEX-measured fluxes, between 145 to 705 Jy km s−1, are compared with previous values taken from Herschel SPIRE FTS. We highlight the great capabilities of APEX for resolving the H2O  line profiles with high spectral resolutions while also improving by a factor of two the significance of the detection within moderate integration times. While exploring the correlation between the p-H2O(211–202) and the total infrared luminosity, our galaxies are found to follow the trend at the bright end of the local ULIRG’s distribution. The p-H2O(211–202) line spectra are compared to the mid-J CO and HCN spectra, and dust continuum previously observed with ALMA. In the complex interacting system IRAS 09022-3615, the profile of the water emission line is offset in velocity with respect to the ALMA CO(J = 4 − 3) emission. For IRAS 17207-0014 and IRAS 06035-7102, the profiles between the water line and the CO lines are spectroscopically aligned. This pilot study demonstrates the feasibility of directly conducting ground-based high-frequency observations of this key water line, opening the possibility of detailed follow-up campaigns to tackle its nature.

Sulfur isotope ratios in the Large Magellanic Cloud

Context. Sulfur isotope ratios have emerged as a promising tool for tracing stellar nucleosynthesis, quantifying stellar populations, and investigating the chemical evolution of galaxies. While they are extensively studied in the context of the Milky Way, they still remain largely unexplored in extragalactic environments. Aims. We focus on investigating the sulfur isotope ratios in the Large Magellanic Cloud (LMC) to gain insights into sulfur enrichment in this nearby system and to establish benchmarks for such ratios in metal-poor galaxies. Methods. We conducted pointed observations of CS and its isotopologues toward N113, one of the most prominent star-formation regions in the LMC, utilizing the Atacama Pathfinder EXperiment 12 m telescope. Results. We present the first robust detection of C33S in the LMC by successfully identifying two C33S transitions on a large scale of ∼5 pc. Our measurements result in an accurate determination of the 34S/33S isotope ratio, which is 2.0 ± 0.2. Our comparative analysis indicates that the 32S/33S and 34S/33S isotope ratios are about a factor of two lower in the LMC than in the Milky Way. Conclusions. Our findings suggest that the low 34S/33S isotope ratio in the LMC can be attributed to a combination of the age effect, low metallicity, and star formation history.

The Quasar Feedback Survey: characterizing CO excitation in quasar host galaxies

ABSTRACT We present a comprehensive study of the molecular gas properties of 17 Type 2 quasars at z < 0.2 from the Quasar Feedback Survey (L$_{\rm [O~{\small III}]}$ > 1042.1 $\rm ergs^{-1}$), selected by their high [O iii] luminosities and displaying a large diversity of radio jet properties, but dominated by LIRG-like galaxies. With these data, we are able to investigate the impact of AGN and AGN feedback mechanisms on the global molecular interstellar medium. Using Atacama Pathfinder EXperiment and ALMA ACA observations, we measure the total molecular gas content using the CO(1-0) emission and homogeneously sample the carbon monoxide (CO) spectral line energy distributions, observing CO transitions (Jup  = 1, 2, 3, 6, 7). We observe high r21 ratios (r21  = L’CO(2-1)/L’CO(1-0)) with a median r21  = 1.06, similar to local (U)LIRGs (with r21 ∼ 1) and higher than normal star-forming galaxies (with r21 ∼ 0.65). Despite the high r21 values, for the seven targets with the required data, we find low excitation in CO(6-5) & CO(7-6) (r61 and r62 < 0.6 in all but one target), unlike high-redshift quasars in the literature, which are far more luminous and show higher line ratios. The ionized gas traced by [O iii] exhibits systematically higher velocities than the molecular gas traced by CO. We conclude that any effects of quasar feedback (e.g. via outflows and radio jets) do not have a significant instantaneous impact on the global molecular gas content and excitation and we suggest that it only occurs on more localized scales.

Linking ice and gas in the Coronet cluster in Corona Australis

Context. During the journey from the cloud to the disc, the chemical composition of the protostellar envelope material can be either preserved or processed to varying degrees depending on the surrounding physical environment. Aims. This works aims to constrain the interplay of solid (ice) and gaseous methanol (CH3OH) in the outer regions of protostellar envelopes located in the Coronet cluster in Corona Australis (CrA), and assess the importance of irradiation by the Herbig Ae/Be star R CrA. CH3OH is a prime test case as it predominantly forms as a consequence of the solid-gas interplay (hydrogenation of condensed CO molecules onto the grain surfaces) and it plays an important role in future complex molecular processing. Methods. We present 1.3 mm Submillimeter Array (SMA) and Atacama Pathfinder Experiment (APEX) observations towards the envelopes of four low-mass protostars in the Coronet cluster. Eighteen molecular transitions of seven species were identified. We calculated CH3OH gas-to-ice ratios in this strongly irradiated cluster and compared them with ratios determined towards protostars located in less irradiated regions such as Serpens SVS 4 in Serpens Main and the Barnard 35A cloud in the λ Orionis region. Results. The CH3OH gas-to-ice ratios in the Coronet cluster vary by one order of magnitude (from 1.2 × 10−4 to 3.1 × 10−3) which is similar to less irradiated regions as found in previous studies. We find that the CH3OH gas-to-ice ratios estimated in these three regions are remarkably similar despite the different UV radiation field intensities and formation histories. Conclusions. This result suggests that the overall CH3OH chemistry in the outer regions of low-mass envelopes is relatively independent of variations in the physical conditions and hence that it is set during the prestellar stage.

Molecular Outgassing in Centaur 29P/Schwassmann–Wachmann 1 during Its Exceptional 2021 Outburst: Coordinated Multiwavelength Observations Using nFLASH at APEX and iSHELL at the NASA-IRTF

The extraordinary 2021 September–October outburst of Centaur 29P/Schwassmann–Wachmann 1 afforded an opportunity to test the composition of primitive Kuiper disk material at high sensitivity. We conducted nearly simultaneous multiwavelength spectroscopic observations of 29P/Schwassmann–Wachmann 1 using iSHELL at the NASA Infrared Telescope Facility (IRTF) and nFLASH at the Atacama Pathfinder EXperiment (APEX) on 2021 October 6, with follow-up APEX/nFLASH observations on 2021 October 7 and 2022 April 3. This coordinated campaign between near-infrared and radio wavelengths enabled us to sample molecular emission from a wealth of coma molecules and to perform measurements that cannot be accomplished at either wavelength alone. We securely detected CO emission on all dates with both facilities, including velocity-resolved spectra of the CO (J = 2–1) transition with APEX/nFLASH and multiple CO (v = 1–0) rovibrational transitions with IRTF/iSHELL. We report rotational temperatures, coma kinematics, and production rates for CO and stringent (3σ) upper limits on abundance ratios relative to CO for CH4, C2H6, CH3OH, H2CO, CS, and OCS. Our upper limits for CS/CO and OCS/CO represent their first values in the literature for this Centaur. Upper limits for CH4, C2H6, CH3OH, and H2CO are the most stringent reported to date, and are most similar to values found in ultra CO-rich Oort cloud comet C/2016 R2 (PanSTARRS), which may have implications for how ices are preserved in cometary nuclei. We demonstrate the superb synergy of coordinated radio and near-infrared measurements, and advocate for future small-body studies that jointly leverage the capabilities of each wavelength.

Observations of neutral carbon in 29 high-z lensed dusty star-forming galaxies and the comparison of gas mass tracers

Context. The nature and evolution of high-redshift dusty star-forming galaxies (high-z DSFGs) remain open questions. Their massive gas reservoirs play an important role in driving the intense star formation rates hosted in these galaxies. Aims. Our aim is to estimate the molecular gas content of high-z DSFGs by using various gas mass tracers, such as the [CI], CO, [CII] emission lines and the dust content. These tracers need to be well calibrated as they are all limited by uncertainties on factors such as αCO, XCI, α[CII], and δGDR, thereby affecting the accurate determination of the gas mass. The main goal of our work is to check the consistency between the gas mass tracers and to cross-calibrate the uncertain factors. Methods. We observed the two [CI] line transitions for 29 South Pole telescope Submillimeter Galaxies (SPT-SMGs) with the Atacama Large Millimeter/submillimeter Array–Atacama Compact Array (ALMA-ACA). Additionally, we also present new Atacama Pathfinder EXperiment (APEX) observations of [CII] line for nine of these galaxies. We combined our observations with the rich ancillary data of low- and mid-J CO lines, ancillary [CII] line, and dust mass estimations for these galaxies. Results. We find a nearly linear relation between the infrared luminosity and [CI] luminosity if we fit the starbursts and main-sequence galaxies separately. We measure a median [CI]-derived excitation temperature of 34.5 ± 2.1 K. We probed the properties of the interstellar medium (ISM), such as density and radiation field intensity, using [CI] to mid- or high-J CO lines and the [CI]-to-infrared luminosity ratio, and find similar values to the SMG populations in the literature. Finally, the gas masses estimated from [CI], CO, dust, and [CII] do not exhibit any significant trend with the infrared luminosity or the dust temperature. We provide the various cross-calibrations between these tracers. Conclusions. Our study confirms that [CI] is a suitable tracer of the molecular gas content, and shows an overall agreement between all the classical gas tracers used at high redshift. However, their absolute calibration, and thus the gas depletion timescale measurements, remain uncertain.

Molecular Environment of the Thermal Composite Supernova Remnant G352.7-0.1

Galactic supernova remnants (SNRs) play an important role in our understanding of supernovae and their feedback on the interstellar environment. SNR G352.7-0.1 is special for its thermal composite morphology and double-ring structure. We have performed spectroscopic mapping of the 12CO and 13CO J = 2–1 lines toward G352.7-0.1 with the Atacama Pathfinder Experiment telescope. Broad 12CO lines are found in the northeastern ring at a local-standard-of-rest velocity range of ∼−50 to −30 km s−1, suggesting that the remnant is interacting with molecular clouds at ∼−51 km s−1. Thus, we adopt a distance of ∼10.5 kpc for this SNR. The momentum and kinetic energy of the shocked gas along the line of sight are estimated to be ∼102 M ☉ km s−1 and ∼1046 erg, respectively. We also find an expanding structure around the remnant, which is possibly related to the wind-blown bubble of the progenitor star. From Fermi-LAT data in the energy range 0.1–500 GeV, we find no gamma-ray counterparts to G352.7-0.1.

The molecular environment of the solar-type protostar IRAS 16293–2422

Context. Studying the physical and chemical processes leading to the formation of low-mass stars is crucial for understanding the origin of our Sun and the Solar System. In particular, analyzing the emission and absorption lines from molecules to derive their spatial distribution in the envelopes of young stellar objects is a fundamental tool to obtain information on the kinematics and chemistry at the very early stages of star formation. Aims. In this work we aim to examine in detail the spatial structures and molecular abundances of material surrounding the very well-known low-mass binary protostar IRAS 16293-2422 and the prestellar core 16293E, which are embedded in the Lynds 1689 N dark cloud. This analysis is performed to obtain information on the physical and chemical properties of these young objects and their interaction with the molecular outflows present across the region. Methods. We have used the LAsMA heterodyne array installed on the Atacama Pathfinder Experiment (APEX) 12 meter submillimeter telescope to image a region of about 0.12 × 0.12 pc2 around IRAS 16293-2422 and 16293E and to study their molecular environment covering 45.6 GHz in a frequency range from 277 GHz to 375 GHz. We have also used the APEX FLASH+ receiver to observe and search for molecular lines in a frequency range between 476 GHz to 493 GHz. Results. We have identified 144 transitions from 36 molecular species, including isotopologues. This is the first time that such a large number of species have been mapped at large scales simultaneously in this region. The maps reveal the envelope to have a complex morphology around the cloud cores and the emission peaks known as E1, E2, W1, W2, and HE2, including the outflow structure arising from IRAS 16293-2422. Using several transitions of para-H2CO, we have derived new lower limits for the kinetic temperatures toward IRAS 16293-2422 and the surrounding emission peaks. Based on these temperatures, new column densities for all detected species were derived around the cloud cores and all emission peaks using the radiative transfer codes CLASS-Weeds, CASSIS, and RADEX. We derived H2 volume densities in Lynds 1689 N based on ortho-H2CO transitions with different upper level energies, varying between 5 × 106 cm−3 and 63 K at IRAS 16293-2422 to values on the order of 1 × 106 cm−3 and 35 K at the other emission peaks. Conclusions. Our new observations further confirm the scenario of an outflow arising from IRAS 16293-2422 interacting with the prestellar core 16293E. This is inferred from the velocity and linewidth gradient shown by several deuterated species closer to the outflow-core interaction region in 16293E. We observe a large-scale velocity gradient across the molecular cloud which coincides with the rotation of the envelope around IRAS 16293-2422 reported previously in the literature. A comparison with JCMT SCUBA-2 450 μm dust continuum maps and our data suggests that emission peak W2 may be related to a colder dust source rather than a shocked region. The newly derived column densities and temperatures for different species, combined with the molecular spatial distribution in all sources, indicate clear chemical differences between the protostellar source, the prestellar core and the shocked positions as a result of the diverse physical conditions at different locations in this region.

A sensitive APEX and ALMA CO(1–0), CO(2–1), CO(3–2), and [CI](1–0) spectral survey of 40 local (ultra-)luminous infrared galaxies

We present a high sensitivity, ground-based spectral line survey of low-J carbon monoxide (CO(Jup → Jup − 1) with Jup = 1, 2, 3) and neutral carbon [CI] 3P1−3P0 ([CI](1–0)) in 36 local ultra-luminous infrared galaxies (ULIRGs) and 4 additional LIRGs, all of which have previous Herschel OH 119 μm observations. The study is based on new single-dish observations conducted with the Atacama Pathfinder Experiment (APEX) and complemented with archival APEX and Atacama Large Millimeter Array (ALMA and ACA) data. Our methods are optimized for a multi-tracer study of the total molecular line emission from these ULIRGs, including any extended low-surface-brightness components. We find a tight correlation between the CO and [CI] line luminosities, which suggests that the emission from CO(1–0) (and CO(2–1)) arises from similar regions as the [CI](1–0), at least when averaged over galactic scales. By using [CI] to compute molecular gas masses, we estimate a median CO-to-H2 conversion factor of ⟨αCO⟩ = 1.7 ± 0.5 M⊙ (K km s−1pc2)−1 for ULIRGs. We derive median galaxy-integrated CO line ratios of 〈r21〉 = LCO(2-1)′/LCO(1-0)′ = 1.09, 〈r31〉 = LCO(3-2)′/LCO(1-0)′ = 0.76, and 〈r32〉 = LCO(3-2)′/LCO(2-1)′ = 0.76, significantly higher than normal star-forming galaxies, confirming the exceptional molecular gas properties of ULIRGs. We find that the r21 and r32 ratios are poor tracers of CO excitation in ULIRGs, while r31 shows a positive trend with LIR and star formation rates and a negative trend with the H2 gas depletion timescales (τdep). Our investigation of CO line ratios as a function of gas kinematics shows no clear trends, except for a positive relation between r21 and σv, which can be explained by CO opacity effects. These ULIRGs are also characterized by high L[CI](1-0)′/LCO(1-0)′ ratios, with a measured median value of ⟨rCICO⟩ = 0.18, higher than values from previous interferometric studies that were affected by missing [CI] line flux. The rCICO values do not show a significant correlation with any of the galaxy properties investigated, including OH outflow velocities and equivalent widths. We find that the widths of [CI](1–0) lines are ∼10% smaller than those of CO lines, and that this discrepancy becomes more significant in ULIRGs with broad lines (σv > 150 km s−1) and when considering the high-v wings of the lines. This suggests that the low optical depth of [CI] can challenge its detection in diffuse, low-surface-brightness outflows and, therefore, its use as a tracer of CO-dark H2 gas in these components. Finally, we find that higher LAGN are associated with longer τdep, consistent with the hypothesis that active galactic nucleus feedback may reduce the efficiency of star formation. Our study highlights the need for sensitive single-dish multi-tracer H2 surveys of ULIRGs that are able to recover the flux that is missed by interferometers, especially in the high-frequency lines such as [CI]. The Atacama Large Aperture Submillimeter Telescope (AtLAST) will be transformational for this field.

The kinematics of the magnetized protostellar core IRAS15398-3359

Context. Observations of protostellar envelopes are essential in order to understand better the process of gravitational collapse toward star and planet formation. From a theoretical perspective, magnetic fields are considered an important factor during the early stages of star formation, especially during the main accretion phase. Aims. Our aim is to study the relation between kinematics and magnetic fields at a very early stage of the star formation process by using data from the Atacama Pathfinder EXperiment (APEX) single-dish antenna with an angular resolution of 28". Methods. We observed the two molecular lines C18O (2–1) and DCO+ (3–2) toward the Class 0 young stellar object IRAS15398-3359. We implemented a multi-component Gaussian fitting on the molecular data to study the kinematics. In addition, we used previous polarization observations on this source to predict the influence of the magnetic field on the core. Results. The velocity gradient along the central object can be explained as an ongoing outflow motion. We report the flowing of material from the filament toward the central object, and the merging of two velocity components in the C18O (2–1) emission around the protostar position, probably due to the merging of filamentary clouds. Our analysis shows that the large-scale magnetic field line observed previously is preferentially aligned to the rotation axis of the core.

Spiral structure and massive star formation in the hub-filament-system G326.27-0.49

ABSTRACT Hub-filament systems (HFSs) are potential sites of formation of star clusters and high mass stars. To understand the HFSs and to provide observational constraints on current theories that attempt to explain star formation globally, we report a study of the region associated with G326.27-0.49 using infrared data of dust continuum and newly obtained observations on molecular tracers using the APEX (Atacama Pathfinder EXperiment) telescope. We use the spectroscopic observations to identify velocity-coherent structures (filaments and clumps) and study their properties at a resolution of 0.4 pc. The region contains two main velocity components: first component shows four filaments between −63 and −55 km s−1 forming a spiral structure converging in a hub, the second filamentary component at ∼−72 km s−1 harbours a massive young stellar object (YSO) and possibly interacts with the hub. The clumps harbouring the three main YSOs in the region are massive (187–535 M⊙), have luminosities consistent with B-type stars, have central densities of ∼106 cm−3, and drive large outflows. Majority of the velocity-coherent clumps in the region shows virial parameters between 2 and 7, which considering the detection of protostars implies collapse to be gradual. We conclude that the region consists of a network of filaments through which mass accretes (∼10−4 M⊙ yr−1) onto the hub. The hub and some of the ends of filaments appear to be undergoing collapse to form new stars. This study identifies a target region for future high-resolution studies that would probe the link between the core and filament evolution.

Dynamics of the star-forming region G345.51+0.84

ABSTRACT With the Atacama Pathfinder Experiment mapping observations of 13CO and C18O (2-1) complemented with Herschel data, we have carried out a comprehensive analysis on dynamics of the G345.51+0.84 (G345 hereafter) region. It is composed of two physically connected components: the blue-shifted (i.e. G345Blue), and red-shifted velocity (i.e. G345Red) clouds, which peak near −12.5  km s−1 and −10.5  km s−1, respectively. The former cloud contains one compact clump (C1), whereas the latter constitutes one filament (Fil345) and four clumps (C2–C5) inside it. The filament is ∼2.6  pc-long and ∼0.52  pc-wide with a median line-mass of Mline = 183 ± 98 M⊙ pc−1, being overall in equilibrium but locally gravitationally bound especially around the clumps. The presence of high-mass protostars in the C2 clump and higher Mline values around it collectively indicates that Fil345 is an ongoing high-mass star-forming filament. The detailed dynamics analysis reveals the cloud–cloud collision scenario between G345Blue and G345Red in the global region studied here, and the longitudinal and radial velocity gradients in the filament indicative of directed mass accretion along the two orthogonal directions. Further analysing the possible mechanism of filament formation for Fil345, we suggest that it presently grows in mass by a hybrid of mass accretion and cloud–cloud collision.

The PhotoDissociation Region Toolbox: Software and Models for Astrophysical Analysis

The PhotoDissociation Region Toolbox provides comprehensive, easy-to-use, public software tools and models that enable an understanding of the interaction of the light of young, luminous, massive stars with the gas and dust in the Milky Way and in other galaxies. It consists of an open-source Python toolkit and photodissociation region (PDR) models for analysis of infrared and millimeter/submillimeter line and continuum observations obtained by ground-based and suborbital telescopes, and astrophysics space missions. PDRs include all of the neutral gas in the interstellar medium where far-ultraviolet photons dominate the chemistry and/or heating. In regions of massive star formation, PDRs are created at the boundaries between the H ii regions and neutral molecular cloud, as photons with energies 6 eV < h ν < 13.6 eV photodissociate molecules and photoionize metals. The gas is heated by photoelectrons from small grains and large molecules and cools mostly through far-infrared (FIR) fine-structure lines like [O i] and [C ii]. The models are created from state-of-the art PDR codes that include molecular freeze-out; recent collision, chemical, and photorates; new chemical pathways, such as oxygen chemistry; and allow for both clumpy and uniform media. The models predict the emergent intensities of many spectral lines and FIR continuum. The tools find the best-fit models to the observations and provide insight into the physical conditions and chemical makeup of the gas and dust. The PDR Toolbox enables novel analysis of data from telescopes such as the Infrared Space Observatory, Spitzer, Herschel, the Stratospheric Terahertz Observatory, the Stratospheric Observatory for Infrared Astronomy, the Submillimeter Wave Astronomy Satellite, the Atacama Pathfinder Experiment, the Atacama Large Millimeter/submillimeter Array, and the JWST.

Millimeter/Submillimeter VLBI with a Next Generation Large Radio Telescope in the Atacama Desert

The proposed next generation Event Horizon Telescope (ngEHT) concept envisions the imaging of various astronomical sources on scales of microarcseconds in unprecedented detail with at least two orders of magnitude improvement in the image dynamic ranges by extending the Event Horizon Telescope (EHT). A key technical component of ngEHT is the utilization of large aperture telescopes to anchor the entire array, allowing the connection of less sensitive stations through highly sensitive fringe detections to form a dense network across the planet. Here, we introduce two projects for planned next generation large radio telescopes in the 2030s on the Chajnantor Plateau in the Atacama desert in northern Chile, the Large Submillimeter Telescope (LST) and the Atacama Large Aperture Submillimeter Telescope (AtLAST). Both are designed to have a 50-meter diameter and operate at the planned ngEHT frequency bands of 86, 230 and 345 GHz. A large aperture of 50 m that is co-located with two existing EHT stations, the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Pathfinder Experiment (APEX) Telescope in the excellent observing site of the Chajnantor Plateau, will offer excellent capabilities for highly sensitive, multi-frequency, and time-agile millimeter very long baseline interferometry (VLBI) observations with accurate data calibration relevant to key science cases of ngEHT. In addition to ngEHT, its unique location in Chile will substantially improve angular resolutions of the planned Next Generation Very Large Array in North America or any future global millimeter VLBI arrays if combined. LST and AtLAST will be a key element enabling transformative science cases with next-generation millimeter/submillimeter VLBI arrays.

SEPIA345: A 345 GHz dual polarization heterodyne receiver channel for SEPIA at the APEX telescope

Context. We describe the new SEPIA345 heterodyne receiver channel installed at the Atacama Pathfinder EXperiment (APEX) telescope, including details of its configuration, characteristics, and test results on sky. SEPIA345 is designed and built to be a part of the Swedish ESO PI Instrument for the APEX telescope (SEPIA). This new receiver channel is suitable for very high-resolution spectroscopy and covers the frequency range 272–376 GHz. It utilizes a dual polarization sideband separating (2SB) receiver architecture, employing superconductor-isolator-superconductor mixers (SIS), and provides an intermediate frequency (IF) band of 4–12 GHz for each sideband and polarization, thus covering a total instantaneous IF bandwidth of 4 × 8 = 32 GHz. Aims. This paper provides a description of the new receiver in terms of its hardware design, performance, and commissioning results. Methods. The methods of design, construction, and testing of the new receiver are presented. Results. The achieved receiver performance in terms of noise temperature, sideband rejection, stability, and other parameters are described. Conclusions. SEPIA345 is a commissioned APEX facility instrument with state-of-the-art wideband IF performance. It has been available on the APEX telescope for science observations since July 2021.