Spectral Survey Research Articles

Extragalactic globular cluster near-infrared spectroscopy

Context. One way to constrain the evolutionary histories of galaxies is to analyse their stellar populations. In the local Universe, our understanding of the stellar population properties of galaxies has traditionally relied on the study of optical absorption and emission-line features. Aims. In order to overcome limitations intrinsic to this wavelength range, such as the age-metallicity degeneracy and the high sensitivity to dust reddening, we must use wavelength ranges beyond the optical. The near-infrared (NIR) offers a possibility to extract information on spectral signatures that are not as obvious in traditional optical bands. Moreover, with the current and forthcoming generation of instrumentation focusing on the NIR, it is mandatory to explore possibilities within this wavelength range for nearby-Universe galaxies. However, although the NIR shows great potential, we are only beginning to understand it. Widely used techniques such as a full spectral fitting and line strength indices need to be tested on systems that are as close to simple stellar populations as possible, and the result from the techniques need to be compared to the yields from a traditional optical analysis. Methods. We present a NIR spectral survey of extragalactic globular clusters (GCs). The set was composed of 21 GCs from the Centaurus A galaxy that were obtained with SOAR/TripleSpec4, which covered the ∼1.0–2.4 μm range with a spectral resolution (R = λ/Δλ) of 3500. These spectra cover Hβ equivalent widths between 0.98 Å and 4.32 Å, and [MgFe]′ between 0.24 Å and 3.76 Å. Results. This set was ideal for performing absorption band measurements and a full spectral fitting, and it can be used for kinematic studies and age and abundance measurements. With this library, we expect to be able to probe the capabilities of NIR models, as well as to further improve stellar population estimates for the GCs around the Centaurus A galaxy.

Chemical composition of comets C/2021 A1 (Leonard) and C/2022 E3 (ZTF) from radio spectroscopy and the abundance of HCOOH and HNCO in comets

We present the results of a molecular survey of long period comets C/2021 A1 (Leonard) and C/2022 E3 (ZTF). Comet C/2021 A1 was observed with the Institut de radioastronomie millim\'etrique (IRAM) 30-m radio telescope in November-December 2021 before perihelion (heliocentric distance 1.22 to 0.76 au) when it was closest to the Earth ($ au). We observed C/2022 E3 in January-February 2023 with the Odin 1-m space telescope and IRAM 30-m, shortly after its perihelion at 1.11 au from the Sun, and when it was closest to the Earth ($ au). Snapshots were obtained during 12--16 November 2021 period for comet C/2021 A1. Spectral surveys were undertaken over the 8--13 December 2021 period for comet C/2021 A1 (8 GHz bandwidth at 3 mm, 16 GHz at 2 mm, and 61 GHz in the 1 mm window) and over the 3--7 February 2023 period for comet C/2022 E3 (25 GHz at 2 mm and 61 GHz at 1 mm). We report detections of 14 molecular species (HCN, HNC CH$_3$CN, HNCO, NH$_2$CHO, CH$_3$OH, H$_2$CO, HCOOH CH$_3$CHO, H$_2$S, CS, OCS, C$_2$H$_5$OH and aGg'-(CH$_2$OH)$_2$) in both comets. In addition, HC$_3$N, and CH$_2$OHCHO were marginally detected in C/2021 A1, and CO and H$_2$O (with Odin ) were detected in C/2022 E3. The spatial distribution of several species (HCN, HNC, CS, H$_2$CO, HNCO, HCOOH, NH$_2$CHO, and CH$_3$CHO) is investigated. Significant upper limits on the abundances of other molecules and isotopic ratios are also presented. The activity of comet C/2021 A1 did not vary significantly between 13 November and 13 December 2021, when observations stopped, just before it started to exhibit major outbursts seen in the visible and from observations of the OH radical. Short-term variability in the outgassing of comet C/2022 E3 of the order of pm 20<!PCT!> is present and possibly linked to its 8h rotation period. Both comets exhibit rather low abundances relative to water for volatile species such as CO ($<2$<!PCT!>) and H$_2$S (0.15<!PCT!>). Methanol is also rather depleted in comet C/2021 A1 (0.9<!PCT!>). Following their revised photo-destruction rates, HNCO and HCOOH abundances in comets observed at millimetre wavelengths have been reevaluated. Both molecules are relatively enriched in these two comets (sim 0.2<!PCT!> relative to water). Since the combined abundance of these two acids (0.1 to 1<!PCT!>) is close to that of ammonia in comets, we cannot exclude that these species could be produced by the dissociation of ammonium formate and ammonium cyanate if present in comets.

Performance predictions of the SPARC x-ray crystal spectrometers for ion temperature and toroidal rotation measurements.

SPARC will be outfitted with three systems of x-ray crystal spectrometer arrays. Two of these are designed using cylindrically bent crystals to achieve high spectral-resolution for ion temperature and toroidal velocity measurements via imaging He-like Kr and Ne-like Xe. The last acts as a spectral survey system to monitor Ne-like W and nearby H- and He-like emission from Cr, Fe, Co, Ni, and Cu. Line radiation intensities are calculated using the Flexible Atomic Code for atomic data and ColRadPy for collisional-radiative modeling, then convoluted with a Voigt line shape. Free-free, free-bound, and two-photon continuum radiation is also included. The ToFu code is used to perform volume-of-sight integration to produce synthetic detector images. In addition, presented is cross-validation performed using the XICSRT Monte Carlo ray-tracing code. Ion temperature and toroidal velocity profiles are reconstructed using ToFu via tomographic inversion.

Investigation of the rotational spectrum of CH$_3$17OH and its tentative detection toward Sagittarius B2(N)

Methanol is an abundant and widespread molecule in the interstellar medium. The column density of its 18O isotopolog, CH$_3$18OH, is in some star-forming regions so high that the search for CH$_3$17OH is promising. But only very few transition frequencies of CH$_3$17OH with a microwave accuracy have been published prior to our investigation. We want to extend the very limited rotational line list of CH$_3$17OH to be able to search for this isotopolog in the interstellar medium. We recorded the rotational spectrum of CH$_3$17OH between 38 and 1095 GHz employing a methanol sample enriched in 17O to 20<!PCT!>. A torsion-rotation Hamiltonian model based on the rho-axis method was employed to fit the data, as in our previous studies. We searched for rotational transitions of CH$_3$17OH in the imaging spectral line survey ReMoCA obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming region Sgr B2(N). The observed spectra were modeled under the assumption of local thermodynamic equilibrium (LTE). The assignments cover $0 J 45$, $K_a 16$, and mainly the $ t = 0$ and 1 torsional states. The Hamiltonian model describes our data well. The model was applied to derive a line list for radio-astronomical observations. We report a tentative detection of CH$_3$17OH along with secure detections of the more abundant isotopologs of methanol toward Sgr B2(N2b). The derived column densities yield isotopic ratios 12C/13C = 25, 16O/18O = 240, and 18O/17O = 3.3, which are consistent with values found earlier for other molecules in Sgr B2. The agreement between the 18O/17O isotopic ratio that we obtained for methanol and the 18O/17O ratios reported in the past for other molecules in Sgr B2(N) strongly supports our tentative interstellar identification of CH$_3$17OH. The accuracy of the derived line list is sufficient for further radio astronomical searches for this methanol isotopolog toward other star-forming regions.

Chemical inventory of the envelope of the Class I protostar L1551 IRS 5

Episodic accretion in protostars leads to luminosity outbursts that end up heating their surroundings. This rise in temperature pushes the snow lines back, enabling the desorption of chemical species from dust grain surfaces, which may significantly alter the chemical history of the accreting envelope. However, a limited number of extensive chemical surveys of eruptive young stars have been performed thus far. In the present study, we carry out a large spectral survey of the binary Class I protostar L1551 IRS 5, known to be a FUor-like object, in the 3 mm and 2mm bands with the IRAM-30m telescope. As a result, we detected more than 400 molecular lines. The source displays a great chemical richness with the detection of 75 species, including isotopologues. Among these species, there are 13 hydrocarbons, 25 N-bearing species, 30 O-bearing species, 15 S-bearing species, 12 deuterated molecules, and a total of 10 complex organic molecules (l-C4H2, CH3CCH, CH2DCCH, CH3CHO, CH3CN, CH3OCH3, CH3OCHO, CH3OH, CH2DOH, and HC5N). With the help of local thermodynamic equilibrium (LTE) and non-LTE models, we determined the column densities of most molecules as well as excitation and kinetic temperatures. While most of those molecules trace the cold envelope (≲20 K), the OCS and CH3OH emission arise from the warm (>100 K) innermost (<2″) regions. We compared the chemical inventory of L1551 IRS 5 and its column density ratios, including isotopic ratios, with other protostellar sources. A broad chemical diversity is seen among Class I objects. More observations with both single-dish telescopes and interferometers are needed to characterize the diversity in a larger sample of protostars, while more astrochemical models would help explain this diversity, in addition to the impact of luminosity outbursts on the chemistry of protostellar envelopes.

Geoenvironmental characteristics of ferroniobium slag from the saint Lawrence columbium mine, Oka, Québec, Canada

Niobium (Nb) is a critical metal usually hosted in pyrochlore and mined from carbonatite deposits. The aluminothermic reduction of pyrochlore concentrate yields ferroniobium (FeNb) alloy and a slag waste. This study presents results from mineralogical, geochemical, and radiochemical investigations of FeNb slag found at the former Saint Lawrence Columbium mine in Oka, Québec, Canada. Slag casts exhibit a vertical zonation resulting from fractional crystallization and differentiation in the melt. Sampling of the slag was designed to characterize resulting chemical and mineralogical variations within casts. The median bulk composition of samples (n = 14) is dominated by Al2O3 (47%) and CaO (16%) from process reagents. The slag also contains significant TiO2 (4%) and trace elements including Zr (6763 ppm), U (601 ppm), and Th (1371 ppm) from pyrochlore that partition preferentially from concentrate to the slag. Based on radiochemical analyses of daughter products and assuming secular equilibrium, median (n = 3) activity concentrations for U and Th decay series are 213 and 111 Bq/g, respectively. A field spectral radiometric survey of the slag disposal area found median (n = 37) equivalent U and Th concentrations of 1069 and 2101 ppm, respectively. The primary mineralogy of the top and middle of slag casts is dominated by hibonite, grossite, and perovskite. Most of the U and Th is hosted by perovskite. The bottom of slag casts is an assemblage of mainly gehlenite, ferri-gehlenite, hercynite, grossite, and anorthite. The casts also contain a (Na,F,Ce) calcium-aluminate glass decreasing in abundance from top to bottom, and a (Na,F,Ce,Ti,Zr) calcium-aluminosilicate glass in the cast bottoms. The (Na,F,Ce) calcium-aluminate glass, grossite, and hibonite are the phases most susceptible to weathering. Perovskite, gehlenite, and hercynite show little or no signs of alteration. A leach test was performed on three columns filled with material from the top, middle, and bottom of casts. In the field, a parallel leach experiment was conducted with three barrels filled with undifferentiated slag material and open to atmospheric conditions. Column leachate was found to be highly alkaline, with pH in the top column reaching 13.2. Median pH values in column and barrel leachate were 10.4 and 9.2, respectively. The maximum U concentration in column leachate was 13 μg/L whereas in barrel leachate it was 65 μg/L. Maximum Th concentrations in column and barrel leachates were 7.65 and 0.2 μg/L, respectively. Median Al concentrations in column and barrel leachates were 74.9 and 3.9 mg/L, respectively. Slag from the production of FeNb is readily weathered and represents a technologically enhanced naturally occurring radioactive material (TENORM) requiring environmental management because of its radioactivity and the alkaline nature of its leachate.

Complex organic molecules uncover deeply embedded precursors of hot cores

Context. During the process of star formation, the dense gas undergoes significant chemical evolution leading to the emergence of a rich variety of molecules associated with hot cores and hot corinos. However, the physical conditions and the chemical processes involved in this evolution are poorly constrained. In particular, the early phases, corresponding to a stage prior to the emergence of any strong ionising emission from the protostar, are still poorly studied. Aims. In this work, we provide a full inventory of the emission from complex organic molecules (COMs) to investigate the physical structure and chemical composition of six high-mass protostellar envelopes. We aim to investigate the conditions for the emergence of COMs in hot cores. Methods. We performed an unbiased spectral survey towards six infrared-quiet massive clumps between 159 GHz and 374 GHz with the APEX 12 m telescope, covering the entire atmospheric windows at 2 mm, 1.2 mm, and 0.8 mm. To identify the spectral lines, we used rotational diagrams and radiative transfer modelling assuming local thermodynamic equilibrium. Results. We detect up to 11 COMs plus three isotopologues, of which at least five COMs (CH3OH, CH3CN, CH3OCHO, CH3OCH3, and CH3CHO) are detected towards all sources. Towards all the objects, most of the COM emission is found to be cold, with respect to the typical temperatures at which COMs are found, with a temperature of 30 K and extended with a size of ~0.3 pc. Although the bulk of the gas for our sample of young massive clumps has a cold temperature, we also detect emission from COMs originating from the immediate vicinity of the protostar. This warm component of the envelope is best traced by methanol and methyl cyanide, in particular methyl cyanide traces a compact (~1″) and the hottest (T ~200 K) component of the envelope. Only three out of the six sources exhibit a robustly detected hot gas component (T > 100 K) traced by several COMs. We find a gradual emergence of the warm component in terms of size and temperature, together with an increasing molecular complexity, allowing us to establish an evolutionary sequence for our sample based on COMs. While they can already be well characterised by an emerging molecular richness, gas temperatures of COMs in the hot gas and molecular abundances suggest that COMs may become abundant in the gas phase at temperatures below the thermal desorption temperature. Conclusions. Our findings confirm that the sources of our sample of infrared-quiet massive clumps are in an early evolutionary stage during which the bulk of the gas is cold. The presence of COMs is found to be characteristic of these early evolutionary stages accompanying high-mass star and cluster formation. While the extent of the compact heated regions resembles that of hot cores, the molecular abundances, except for complex cyanides, resemble those of hot corinos and are lower than the peak COM abundances of hot cores. We suggest that the emergence of hot cores is preceded by a phase in which mostly O-bearing COMs appear first with similar abundances to hot corinos albeit with larger source sizes.

SPHEREx payload thermal architecture and analysis

The SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) is an all-sky spectral survey in a Sun-synchronous low earth orbit. It measures spectrum in the near infrared band from 0.75 µm to 5 µm. To achieve this wavelength coverage, the instrument has two focal plane arrays, both passively cooled at <55 K (mid-wave infrared) and <80 K (short-wave infrared). Additionally, the instrument requires no moving parts for spectral resolution, relying instead on spacecraft-controlled pointing. A thermally isolating structure and a set of V-groove radiators reduce the heat flow conducted and radiated from the spacecraft bus. The thermal system also blocks the incident solar flux and earth radiation from reaching the sensitive cryogenic instrument while still allowing substantial pointing flexibility. The combination of passive cryogenic cooling and survey requirements in a sun exposed low earth orbit environment presents a challenge for the thermal design. This paper will discuss the SPHEREx payload overall thermal architecture, bounding thermal environments, the component thermal design, and analysis of on-flight performance.

ALMA Spectral Survey of an Eruptive Young Star, V883 Ori (ASSAY). I. What Triggered the Current Episode of Eruption?

An unbiased spectral survey of V883 Ori, an eruptive young star, was carried out with the Atacama Large Millimeter/submillimeter Array in Band 6. The detected line emission from various molecules reveals morphological/kinematical features in both the Keplerian disk and the infalling envelope. A direct infall signature, redshifted absorption against the continuum, has been detected in CO, HCO+, HCN, HNC, and H2CO. HCO+ and SO show large armlike structures that probably connect the infalling envelope to the disk. HCN and H2CO reveal a distinct boundary between the inner and outer disks and tentative spiral structures connecting the outer disk to the inner disk. HNC shows a large central emission hole (r ∼ 0.″3) due to its chemical conversion to HCN at high temperatures. HDO emission, a direct tracer of the water sublimation region, has been detected in the disk. Molecular emission from complex organic molecules is confined within the HDO emission boundary, and HCO+ has an emission hole in its distribution due to its destruction by water. Together, these features suggest that the current episode of eruption in V883 Ori may be triggered by the infall from the envelope to the outer disk, generating a spiral wave that propagates inward and greatly enhances the accretion onto the central star.

Zn(II), Mn(III), and Co(III) complexes of Schiff base derived from 2‐hydroxy‐1‐naphthaldehyde: Synthesis, spectral surveys, single crystal structure studies, Hirshfeld surface analysis, density functional theory calculation, molecular electrostatic potential, and molecular docking evaluations

A new series of transition metal complexes of bidentate Schiff base compound derived from 2‐hydroxy‐1‐(2‐methoxyethylimino)‐naphthalene (HL) were synthesized and characterized using elemental analysis, Fourier transform infrared spectroscopy (FT‐IR), and UV–vis spectroscopies. X‐ray single crystal structures of Zn(II), Mn(III), and Co(III) complexes (1–4) have also been determined, and it was indicated that these Zn(II) and Co(III) complexes (1, 4) are in an octahedral geometry. Whereas, it was found that the Zn complex (2) is in quite a regular tetrahedral environment. Also, the Mn center in complex (3) is ligated by two azomethine nitrogen atoms, two ligand oxygen atoms, and one Cl atom of metal salt forming five coordinated tetragonal pyramid geometry around the Mn atoms. The cyclic voltammetry of the complexes specifies an irreversible redox behavior for all complexes (1–4). Next, DFT/B3LYP theoretical method was used to determine the optimal geometrical configurations and comparison between experimental and theoretical data, as well as for calculations of molecular electrostatic potential, highest‐occupied molecular orbital (HOMO)‐lowest‐unoccupied molecular orbital (LUMO) energy values of selected compounds. The study of non‐covalent interactions was done by Hirshfeld surface analysis using CrystalExplorer program. Furthermore, molecular docking inspection was carried out to study the binding affinity of the tested complexes towards protein B‐cell lymphorna (PDB ID: 4LXD). Using the results obtained from the molecular docking and the summarized interaction of the binding processes, these structures show the validity of effective inhibition against liver cancer.

Magnetic Activity of Millions of G-type Stars Based on the LAMOST DR10 Low-resolution Spectral and TESS Light-curve Surveys and the Future CSST Survey

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) data release 10 (DR10) provides over 3 million G-type stellar spectra, which are important for the study of chromospheric activity of solar-like stars. We have used the iSpec program to perform spectral subtraction on the G-type stellar spectra obtained from LAMOST DR10 with a signal-to-noise ratio greater than 10. We have calculated the magnetic activity of G-type stars using Hα lines and analyzed the Hα variation. Among the more than 3 million spectra from more than 2.3 million stars, a total of 220,000 stars show excess chromospheric activity. There were a total of about 480,000 stars with repeated observations. About 390,000 stars were found to exhibit variations in the Hα line, and 14,000 stars showed changes in their radial velocity. By using the Gaia data, we determined the distances of these stars above the Galactic disk. We first concluded that the fraction of G-type active stars decreases with increasing distance above the Galactic disk. By using the Transiting Exoplanet Survey Satellite light curves, we obtained the effective fluctuation range of the light curve caused by the starspot and confirmed that there was a positive correlation between the starspot and chromospheric activity. We also concluded that RHα′ tends to be stable for Rossby number (Ro) < 0.13 and that RHα′ decreases as Ro increases in the region Ro ≥ 0.13.

Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars

Context. Asymptotic giant branch (AGB) stars are major contributors to the chemical enrichment of the interstellar medium through nucleosynthesis and extensive mass loss. Direct measures of both processes can be obtained by studying their circumstellar envelopes in molecular line emission. Most of our current knowledge of circumstellar chemistry, in particular in a C-rich environment, is based on observations of the carbon star IRC +10216. Aims. We aim to obtain a more generalised understanding of the chemistry in C-rich AGB circumstellar envelopes by studying a sample of three carbon stars, IRAS 15194–5115, IRAS 15082–4808, and IRAS 07454–7112, and to observationally test the archetypal status often attributed to IRC +10216. Methods. We performed spatially resolved, unbiased spectral surveys in ALMA Band 3 (85–116 GHz). We estimated the sizes of the molecular emitting regions using azimuthally averaged radial profiles of the line brightness distributions. We derived abundance estimates, using a population diagram analysis for molecules with multiple detected lines, and using single-line analytical calculations for the others. Results. We identify a total of 132 rotational transitions from 49 molecular species. There are two main morphologies of the brightness distributions: centrally peaked (CS, SiO, SiS, HCN) and shell-like (CN, HNC, C2H, C3H, C4H, C3N, HC5N, c-C3H2). The brightness distributions of HC3N and SiC2 have both a central and a shell component. The qualitative behaviour of the brightness distributions of all detected molecules, in particular their relative locations with respect to the central star, is the same for all three stars, and consistent with those observed towards IRC +10216. Of the shell distributions, the cyanopolyynes peak at slightly smaller radii than the hydrocarbons, and CN and HNC show the most extended emission. The emitting regions for each species are the smallest for IRAS 07454–7112, consistent with this object having the lowest circumstellar density within our sample. We find that, within the uncertainties of the analysis, the three stars present similar abundances for most species, and also compared to IRC +10216. We find, tentatively, that SiO is more abundant in our three stars compared to IRC+10216, and that the hydrocarbons are under-abundant in IRAS 07454–7112 compared to the other stars and IRC +10216. Our estimated 12C/13C ratios match well the literature values for the three sources and our estimated silicon and sulphur isotopic ratios are very similar across the three stars and IRC +10216. Conclusions. The observed circumstellar chemistry appears very similar across our sample and compared to that of IRC +10216, both in terms of the relative location of the emitting regions and molecular abundances. This implies that, to a first approximation, the chemical models tailored to IRC +10216 are, at least, able to reproduce the observed chemistry in C-rich envelopes across roughly an order of magnitude in wind density.

A λ 3 mm Line Survey toward the Circumstellar Envelope of the Carbon-rich AGB Star IRC+10216 (CW Leo)

We present an unbiased λ 3 mm spectral line survey (between 84.5 and 115.8 GHz), conducted by the Purple Mountain Observatory 13.7 m radio telescope, together with updated modeling results, toward the carbon-rich asymptotic giant branch star IRC+10216 (CW Leo). A total of 75 spectral lines (96 transitions) are detected, and identified to arise from 19 molecules: C2H, l-C3H, C4H, CN, C3N, HC3N, HC5N, HCN, HNC, CH3CN, MgNC, CO, c-C3H2, SiC2, SiO, SiS, CS, C2S, C3S, and their isotopologues. Among them, one molecular emission line (H13CCCN J = 13–12) is discovered in IRC+10216 for the first time. The excitation temperature, column density, and fractional abundance of the detected species are deduced by assuming they are in local thermodynamic equilibrium. In addition, the isotopic ratios of [12C]/[13C], [32S]/[34S], [28Si]/[29Si], and [12C34S]/[13C32S] are obtained and found to be consistent with previous studies. Finally, we summarize all of the 106 species detected in IRC+10216 to date with their observed and modeled column densities for the convenience of future studies.

The ALCHEMI Atlas: Principal Component Analysis Reveals Starburst Evolution in NGC 253

Molecular lines are powerful diagnostics of the physical and chemical properties of the interstellar medium (ISM). These ISM properties, which affect future star formation, are expected to differ in starburst galaxies from those of more quiescent galaxies. We investigate the ISM properties in the central molecular zone of the nearby starburst galaxy NGC 253 using the ultrawide millimeter spectral scan survey from the Atacama Large Millimeter/submillimeter Array Large Program ALCHEMI. We present an atlas of velocity-integrated images at a 1.″6 resolution of 148 unblended transitions from 44 species, including the first extragalactic detection of HCNH+ and the first interferometric images of C3H+, NO, and HCS+. We conduct a principal component analysis (PCA) on these images to extract correlated chemical species and to identify key groups of diagnostic transitions. To the best of our knowledge, our data set is currently the largest astronomical set of molecular lines to which PCA has been applied. The PCA can categorize transitions coming from different physical components in NGC 253 such as (i) young starburst tracers characterized by high-excitation transitions of HC3N and complex organic molecules versus tracers of on-going star formation (radio recombination lines) and high-excitation transitions of CCH and CN tracing photodissociation regions, (ii) tracers of cloud-collision-induced shocks (low-excitation transitions of CH3OH, HNCO, HOCO+, and OCS) versus shocks from star formation-induced outflows (high-excitation transitions of SiO), as well as (iii) outflows showing emission from HOC+, CCH, H3O+, CO isotopologues, HCN, HCO+, CS, and CN. Our findings show these intensities vary with galactic dynamics, star formation activities, and stellar feedback.

The GUAPOS project – V: The chemical ingredients of a massive stellar protocluster in the making

ABSTRACT Most stars, including the Sun, are born in rich stellar clusters containing massive stars. Therefore, the study of the chemical reservoir of massive star-forming regions is crucial to understand the basic chemical ingredients available at the dawn of planetary systems. We present a detailed study of the molecular inventory of the hot molecular core G31.41+0.31 from the project GUAPOS (G31.41+0.31 Unbiased ALMA sPectral Observational Survey). We analyse 34 species for the first time plus 20 species analysed in previous GUAPOS works, including oxygen, nitrogen, sulfur, phosphorus, and chlorine species. We compare the abundances derived in G31.41+0.31 with those observed in other chemically-rich sources that represent the initial and last stages of the formation of stars and planets: the hot corino in the Solar-like protostar IRAS 16293-2422 B, and the comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen. The comparative analysis reveals that the chemical feedstock of the two star-forming regions are similar. The abundances of oxygen- and nitrogen-bearing molecules exhibit a good correlation for all pair of sources, including the two comets, suggesting a chemical heritage of these species during the process of star formation, and hence an early phase formation of the molecules. However, sulfur- and phosphorus-bearing species present worse correlations, being more abundant in comets. This suggests that while sulfur- and phosphorus-bearing species are pre-dominantly trapped on the surface of icy grains in the hot close surroundings of protostars, they could be more easily released into gas phase in comets, allowing their cosmic abundances to be almost recovered.

High-contrast JWST-MIRI Spectroscopy of Planet-forming Disks for the JDISC Survey

The JWST Disk Infrared Spectral Chemistry Survey (JDISCS) aims to understand the evolution of the chemistry of inner protoplanetary disks using the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST). With a growing sample of >30 disks, the survey implements a custom method to calibrate the MIRI Medium Resolution Spectrometer (MRS) to contrasts of better than 1:300 across its 4.9–28 μm spectral range. This is achieved using observations of Themis family asteroids as precise empirical reference sources. The high spectral contrast enables precise retrievals of physical parameters, searches for rare molecular species and isotopologues, and constraints on the inventories of carbon- and nitrogen-bearing species. JDISCS also offers significant improvements to the MRS wavelength and resolving power calibration. We describe the JDISCS calibrated data and demonstrate their quality using observations of the disk around the solar-mass young star FZ Tau. The FZ Tau MIRI spectrum is dominated by strong emission from warm water vapor. We show that the water and CO line emission originates from the disk surface and traces a range of gas temperatures of ∼500–1500 K. We retrieve parameters for the observed CO and H2O lines and show that they are consistent with a radial distribution represented by two temperature components. A high water abundance of n(H2O) ∼ 10−4 fills the disk surface at least out to the 350 K isotherm at 1.5 au. We search the FZ Tau environs for extended emission, detecting a large (radius of ∼300 au) ring of emission from H2 gas surrounding FZ Tau, and discuss its origin.

The First Ka-band (26.1–35 GHz) Blind Line Survey toward Orion KL

We conducted a Ka-band (26.1–35 GHz) line survey toward Orion KL using the TianMa 65 m Radio Telescope (TMRT). It is the first blind line survey in the Ka band and achieves a sensitivity at the mK level (1–3 mK at a spectral resolution of ∼1 km s−1). In total, 592 Gaussian features are extracted. Among them, 257 radio recombination lines (RRLs) are identified. The maximum Δn of RRLs of H, He, and C are 20, 15, and 5, respectively. Through stacking, we have detected the β lines of ion RRLs (RRLs of C+ with the possible contribution of other ions like O+) for the first time, and a tentative signal of the γ lines of ion RRLs can also be seen on the stacked spectrum. Besides this, 318 other line features were assigned to 37 molecular species, and 10 of these species were not detected in the Q-band survey of TMRT. The vibrationally excited states of nine species were also detected. The emission of most species can be modeled under LTE. A number of transitions of E-CH3OH (J 2 − J 1) display maser effects, which are confirmed by our modeling, and besides the bumping peak at J ∼ 6, there is another peak at J ∼ 13. Methylcyanoacetylene (CH3C3N) is detected in Orion KL for the first time. This work emphasizes that the Ka band, which was long ignored for spectral line surveys, is very useful for surveying RRLs and molecular lines simultaneously.

The GUAPOS project: G31.41+0.31 Unbiased ALMA sPectral Observational Survey

Context. The astrochemistry of the important biogenic element phosphorus (P) is still poorly understood, but observational evidence indicates that P-bearing molecules are likely associated with shocks. Aims. We study P-bearing molecules and some shock tracers towards one of the chemically richest hot molecular cores, G31.41+0.31, in the framework of the project “G31.41+0.31 Unbiased ALMA sPectral Observational Survey” (GUAPOS), which is being carried out with the Atacama Large Millimeter Array (ALMA). Methods. We observed the molecules PN, PO, SO, SO2, SiO, and SiS through their rotational lines in the spectral range 84.05– 115.91 GHz covered by the GUAPOS project. Results. PN is clearly detected, while PO is tentatively detected. The PN emission arises from two regions southwest of the hot core peak, named regions 1 and 2 here, and is undetected or tentatively detected towards the hot core peak. The PN and SiO lines are very similar both in spatial emission morphology and spectral shape. Region 1 is partly overlapping with the hot core and is warmer than region 2, which is well separated from the hot core and located along the outflows identified in previous studies. The SO, SO2, and SiS emissions are also detected towards the PN-emitting regions 1 and 2, but arise mostly from the hot core. Moreover, the column density ratio SiO/PN remains constant in regions 1 and 2, while SO/PN, SiS/PN, and SO2/PN decrease by about an order of magnitude from region 1 to region 2, indicating that SiO and PN have a common origin even in regions with different physical conditions. The PO/PN ratio in region 2, where PO is tentatively detected, is ~0.6–0.9, which is in line with the predictions of pure shock models. Conclusions. Our study provides robust confirmation of previous observational evidence that PN emission is tightly associated with SiO and is likely a product of shock chemistry, as the lack of a clear detection of PN towards the hot core allows us to rule out relevant formation pathways in hot gas. We propose the PN-emitting region 2 as a new astrophysical laboratory for shock-chemistry studies.

ALMA High-resolution Spectral Survey of Thioformaldehyde (H2CS) toward Massive Protoclusters

Investigating the temperature and density structures of gas in massive protoclusters is crucial for understanding the chemical properties therein. In this study, we present observations of the continuum and thioformaldehyde (H2CS) lines at 345 GHz of 11 massive protoclusters using the Atacama Large Millimeter/submillimeter Array telescope. High spatial resolution and sensitivity observations have detected 145 continuum cores from the 11 sources. H2CS line transitions are observed in 72 out of 145 cores, including line-rich cores, warm cores, and cold cores. The H2 column densities of the 72 cores are estimated from the continuum emission, which are larger than the density threshold value for star formation, suggesting that H2CS can be widely distributed in star-forming cores with different physical environments. The rotation temperature and column density of H2CS are derived using the XCLASS software. The results show that the H2CS abundances increase as temperature rises and higher gas temperatures are usually associated with higher H2CS column densities. The abundances of H2CS are positively correlated with its column density, suggesting that the H2CS abundances are enhanced from cold cores, warm cores, and line-rich cores in star-forming regions.

Efficient selection of gravitationally lensed OH megamasers with MeerKAT and the Square Kilometre Array

ABSTRACT There has been a recent resurgence in hydroxyl (OH) megamaser research driven by Square Kilometre Array (SKA) precursor/pathfinder telescopes. This will continue in the lead-up to the SKA mid-frequency array, which will greatly expand our view of OH megamasers and their cosmic evolution over ≳80 per cent of the age of the Universe. This is expected to yield large scientific returns as OH megamasers trace galaxy mergers, extreme star formation, high molecular gas densities, and potentially binary/dual supermassive black hole systems. In this paper, we predict the distortion to the OH luminosity function that a magnification bias will inflict, and in turn, predict the distortion on the OH megamaser number counts as a function of redshift. We identify spectral flux density thresholds that will enable efficient lensed OH megamaser selection in large spectral line surveys with MeerKAT and SKA. The surface density of lensed galaxies that could be discovered in this way is a strong function of the redshift evolution of the OH megamaser luminosity function, with predictions as high as ∼1 lensed OH source per square degree at high redshifts (z ≳ 1) for anticipated SKA spectral line survey designs. This could enable efficient selection of some of the most highly obscured galaxies in the Universe. This high-redshift selection efficiency, in combination with the large survey speed of the SKA at ≲1 GHz frequencies and the high magnifications possible with compact OH emission regions (μOH ≫ 10), will enable a transformational view of OH in the Universe.