Search

We study the contribution of various astrophysical events asymptotic giant branch (AGB stars, core collapse and thermonuclear supernovae, neutron star mergers, and collapsars) to the abundances of elements both up to and heavier than the iron peak in a Local Group dwarf irregular galaxy, Wolf–Lundmark–Melotte (WLM). Its star formation history has been recently determined by observations with the JWST , and we use it to estimate the occurrence of the astrophysical sources. The rates of the gas accretion and the outflow are roughly determined based on the stellar metallicity distribution, the oxygen abundance of H  ii regions, and the gas fraction. As discussed in the literature, the difference in time-scales on which the astrophysical events release the nucleosynthesis products is seen in the occurrence of the events and the evolution of abundance ratios. WLM has an extended star formation history and massive stars are recently and currently formed. Thus, the contribution of rotating massive stars through the weak s-process appears in the abundance ratios of light trans-iron elements to iron at later time of the evolution. [ABSTRACT FROM AUTHOR]

Recent observations of high-redshift galaxies have revealed starburst galaxies with excessive amounts of nitrogen, well above that expected in standard evolutionary models. The Sunburst Arc galaxy, particularly its young and massive star cluster, represents the closest (⁠|$z=2.4$|⁠) and brightest of these as a strongly lensed object. In this work, we study the chemical history of this star cluster to determine the origin of the elevated gas-phase nitrogen using a chemical evolution model. Our model includes the enrichment of OB stars through stellar winds and core-collapse supernovae assuming that massive stars (⁠|$M\gt 25$|   |$\mathrm{ M}_\odot$|⁠) collapse directly into black holes at the end of their lives. We fit the model parameters to the observed chemical abundances of the Sunburst Arc cluster: O/H, C/O, and N/O. We find that the observed chemical abundances can be explained by models featuring intense star formation events, characterized by rapid gas accretion and high star formation efficiencies. Additionally, the stellar population contributing to the gas enrichment must exclude Wolf–Rayet stars. These conditions might be present in other nitrogen-rich objects as their similar chemical abundances suggest a common history. As previous studies have proposed the presence of Wolf–Rayet stars in the new nitrogen-rich objects, further research using chemodynamic modeling is necessary to ascertain the true nature of these objects. [ABSTRACT FROM AUTHOR]

Phosphorous species are of great interest in interstellar chemistry since they are the basic blocks for building life here on Earth. Modelling the abundance and environment of recently detected PO |$^{+}$| under non-local thermodynamic equilibrium (LTE) requires rotational spectra of the molecule along with accurate collisional rates with the most abundant species, hydrogen and helium. A new 4D ab initio potential energy surface (PES) of PO |$^{+}$| – H |$_{2}$| collision is calculated using CCSD(T)/CBS(DTQ) methodology considering rigid rotor approximation. The region containing the minima of the PES is augmented using neural networks (NNs) model while very high potentials (⁠|$\gt 2500$| cm |$^{-1}$| ) and asymptotic region have been approximated using Slater and R |$^{-4}$| functions, respectively. The close coupling calculations have been performed using molscat software for both ortho and para -H |$_{2}$| . The rate coefficients have been reported for transitions |$j-j^{\prime }=$| |$1-0$|⁠ , |$2-1$|⁠ , |$3-2$|⁠ , and |$5-4$| through which PO |$^{+}$| has been experimentally detected in interstellar medium (ISM). The rate coefficients for even and odd transitions of PO |$^{+}$| with para -H |$_{2}$| are compared with that of helium and are found to be 1.1–2.0 times higher. For even transitions (|$\Delta j = 2$|), the ortho -H |$_{2}$| rates are 10 per cent higher than para -H |$_{2}$| rates. However, the trend reverses in the case of odd transitions (|$\Delta j = 1$|) when higher J transitions are considered at low temperatures. At higher temperatures, the ortho rates cross the para -H |$_{2}$| rates and become larger than the latter. The new rate coefficients with both ortho and para -H |$_{2}$| will enable accurate modelling of the PO |$^{+}$| abundance in the ISM under non-LTE conditions. [ABSTRACT FROM AUTHOR]

Modelling complex line emission in the interstellar medium (ISM) is a degenerate high-dimensional problem. Here, we present McFine , a tool for automated multicomponent fitting of emission lines with complex hyperfine structure, in a fully automated way. We use Markov chain Monte Carlo (MCMC) to efficiently explore the complex parameter space, allowing for characterizing model denegeracies. This tool allows for both local thermodynamic equilibrium (LTE) and radiative-transfer (RT) models. McFine can fit individual spectra and data cubes, and for cubes encourage spatial coherence between neighbouring pixels. It is also built to fit the minimum number of distinct components, to avoid overfitting. We have carried out tests on synthetic spectra, where in around 90 per cent of cases it fits the correct number of components, otherwise slightly fewer components. Typically, |$T_{\rm ex}$| is overestimated and |$\tau$| underestimated, but accurate within the estimated uncertainties. The velocity and line widths are recovered with extremely high accuracy, however. We verify McFine by applying to a large Atacama Large Millimeter/submillimeter Array (ALMA) N |$_2$| H |$^+$| mosaic of an high-mass star forming region, G316.75−00.00. We find a similar quality of fit to our synthetic tests, aside from in the active regions forming O-stars, where the assumptions of Gaussian line profiles or LTE may break down. To show the general applicability of this code, we fit CO(J = 2-1) observations of NGC 3627, a nearby star-forming galaxy, again obtaining excellent fit quality. McFine provides a fully automated way to analyse rich data sets from interferometric observations, is open source, and pip -installable. [ABSTRACT FROM AUTHOR]

Heterocycles have not been detected in the interstellar medium (ISM) yet. However, the direct involvement of some pentagonal heterocycles within the formation of key biomolecules for the origin of life makes the search for these systems in the ISM relevant for understanding whether some of the bricks of life could be formed in the ISM. We have explored the possible formation of the simple heterocycle furan (c-C |$_{4}$| H |$_{4}$| O) under interstellar conditions, through the reaction between two interstellar species, |$\mathrm{syn}$| -vinyl alcohol (⁠|$\mathrm{syn}$| -VA) and the CCH radical. We employed state-of-the-art quantum-chemical calculations to elucidate the reaction mechanism between the reaction of CCH radical and |$\mathrm{syn}$| -VA. Kinetic simulations were carried out aiming to quantitatively assess the viability of this reaction in the ISM. We have found a reaction pathway to furan where all energy barriers are submerged. However, the formation of this heterocycle is not feasible because the intermediates leading to furan can evolve through more favourable routes. In contrast, we have found viable pathways for the formation of the four isomers of 1-butenol-3-yne (HCCCHCHOH) (Z - |$\mathrm{syn}$|⁠ , E - |$\mathrm{syn}$|⁠ , E - |$\mathrm{anti}$|⁠ , and Z - |$\mathrm{anti}$|⁠), which thus are promising species to be detected in the ISM. Our theoretical work indicates that the four isomers of 1-butenol-3-yne should be present in the ISM because the precursors are known interstellar species, and the kinetic simulations indicate that their formation is very likely. We then encourage the observational search of these molecules in the ISM. [ABSTRACT FROM AUTHOR]

Molecular deuteration is a powerful diagnostic tool for probing the physical conditions and chemical processes in astrophysical environments. In this work, we focus on formaldehyde deuteration in the protobinary system NGC 1333 IRAS 4A, located in the Perseus molecular cloud. Using high-resolution (⁠|$\sim$| 100 au) ALMA (The Atacama Large Millimeter/submillimeter Array) observations, we investigate the [D |$_2$| CO]/[HDCO] ratio along the cavity walls of the outflows emanating from IRAS 4A1. Our analysis reveals a consistent decrease in the deuteration ratio (from |$\sim$| 60-20 per cent to |$\sim$| 10 per cent) with increasing distance from the protostar (from |$\sim$| 2000 to |$\sim$| 4000 au). Given the large measured [D |$_2$| CO]/[HDCO], both HDCO and D |$_2$| CO are likely injected by the shocks along the cavity walls into the gas-phase from the dust mantles, formed in the previous prestellar phase. We propose that the observed [D |$_2$| CO]/[HDCO] decrease is due to the density profile of the prestellar core from which NGC 1333 IRAS 4A was born. When considering the chemical processes at the base of formaldehyde deuteration, the IRAS 4A's prestellar precursor had a predominantly flat density profile within 3000 au and a decrease of density beyond this radius. [ABSTRACT FROM AUTHOR]

We report a significantly tighter trend between gaseous N/O and |$M_*/R_\mathrm{ e}$| (a proxy for gravitational potential) than has previously been reported between gaseous metallicity and |$M_*/R_\mathrm{ e}$|⁠ , for star-forming galaxies in the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. We argue this result to be a consequence of deeper potential wells conferring greater resistance to metal outflows while also being associated with earlier star-formation histories, combined with N/O being comparatively unaffected by metal-poor inflows. The potential–N/O relation thus appears to be both more resistant to short time-scale baryonic processes and also more reflective of a galaxy's chemical evolution state, when compared to previously considered relations. [ABSTRACT FROM AUTHOR]

In order to understand galaxy growth evolution, it is critical to constrain the evolution of its building block: gas. Mostly comprised by Hydrogen in its neutral (H  i) and molecular (H |$_2$|⁠) phases, the latter is the one mostly directly associated to star formation, while the neutral phase is considered the long-term gas reservoir. In this work, we make use of an empirical relation between dust emission at millimetre wavelengths and total gas mass in the interstellar medium (M |$_{\rm HI}$| plus M |$_{\rm H_2}$|⁠) in order to retrieve the H  i content in galaxies. We assemble an heterogeneous sample of 335 galaxies at |$0.01\lt z\lt 6.4$| detected in both mm-continuum and carbon monoxide (CO), with special focus on a blindly selected sample to retrieve H  i cosmological content when the Universe was |$\sim 2-6\,$|  Gyr old (⁠|$1\lt z\lt 3$|⁠). We find no significant evolution with redshift of the M |$_{\rm HI}$| /M |$_{\rm H_2}$| ratio, which is about |$1-3$| (depending on the relation used to estimate M |$_{\rm HI}$|⁠). This also shows that M |$_{\rm H_2}$| -based gas depletion times are underestimated overall by a factor of |$2-4$|⁠. Compared to local Universe H  i mass functions, we find that the number density of galaxies with M |$_{\rm HI}\gtrsim 10^{10.5}\,$| M |$_\odot$| significantly decreased since 8–12 Gyr ago. The specific sample used for this analysis is associated to 20–50 per cent of the total cosmic H  i content as estimated via Damped Lyman- |$\alpha$| Absorbers. In IR luminous galaxies, H  i mass content decreases between |$z\sim 2.5$| and |$z\sim 1.5$|⁠ , while H |$_2$| seems to increase. We also show source detection expectations for SKA surveys. [ABSTRACT FROM AUTHOR]

Aminoacetonitrile (AAN), also known as glycinenitrile, has been suggested as a possible precursor of glycine and adenine in the interstellar medium. Here, we present the chemical modelling of AAN and its isomers in hot cores using the three-phase chemical model NAUTILUS with the addition of over 300 chemical reactions of the three AAN isomers and related species. Our models predicted a peak gas-phase abundance of AAN reaching the order of 10 |$^{-8}$|⁠ , which is consistent with observation towards Sgr B2(N). Regarding the reaction pathways of AAN and its isomers, we found that AAN is primarily formed via free radical reactions on grain surfaces during the early evolutionary stages. Subsequently, it is thermally desorbed into the gas phase as the temperature rises and is then destroyed by positive ions and radicals in gas phase. The isomers of AAN are formed through the hydrogenation reaction of CH |$_3$| NCN on the grain surface and via electron recombination reactions of ion C |$_2$| H |$_5$| N |$_2^+$| in gas phase. We speculate that there is a possibility for NCCN and AAN to react with each other, eventually leading to the formation of adenine in hot cores. However, further investigation is required to understand the efficiency of grain surfaces in adenine formation, through theoretical calculations or laboratory experiments in future research. [ABSTRACT FROM AUTHOR]

In the absence of laboratory data, state-of-the-art quantum chemical approaches can provide estimates of the binding energy (BE) of interstellar species with grains. Without BE values, contemporary astrochemical models are compelled to utilize wild guesses, often delivering misleading information. Here, we employed a fully quantum chemical approach to estimate the BE of seven diatomic radicals – CH, NH, OH, SH, CN, NS, and NO – that play a crucial role in shaping the interstellar chemical composition, using a suitable amorphous solid water model as a substrate since water is the principal constituent of interstellar ice in dense and shielded regions. While the BEs are compatible with physisorption, the binding of CH in some sites shows chemisorption, in which a chemical bond to an oxygen atom of a water molecule is formed. While no structural change has been observed for the CN radical, it is believed that the formation of a hemibonded system between the outer layer of the water cluster and the radical is the reason for the unusually large BE in one of the binding sites considered in our study. A significantly lower BE for NO, consistent with recent calculations, is obtained, which helps explain the recently observed HONO/NH2OH and HONO/HNO ratios in the low-mass hot corino IRAS 16293–2422 B with chemical models. [ABSTRACT FROM AUTHOR]

Context. In stars, metallicity is usually traced using Fe, while in nebulae, O serves as the preferred proxy. Both elements have different nucleosynthetic origins and are not directly comparable. Additionally, in ionized nebulae, Fe is heavily depleted onto dust grains. Aims. We investigate the distribution of Fe gas abundances in a sample of 452 star-forming nebulae with [Fe III] λ4658 detections and their relationship with O and N abundances. Additionally, we analyze the depletion of Fe onto dust grains in photoionized environments. Methods. We homogeneously determined the chemical abundances with direct determinations of electron temperature (Te), considering the effect of possible internal variations of this parameter. We adopted a sample of 300 Galactic stars to interpret the nebular findings. Results. We find a moderate linear correlation (r = −0.59) between Fe/O and O/H. In turn, we report a stronger correlation (r = −0.80) between Fe/N and N/H. We interpret the tighter correlation as evidence that Fe and N are produced on similar timescales while Fe- dust depletion scales with the Fe availability. The apparently flat distribution between Fe/N and N/H in Milky Way stars supports this interpretation. We find that when 12+log(O/H)<7.6, the nebulae seem to reach a plateau value around log(Fe/O) ≈ −1.7. If this trend were confirmed, it would be consistent with a very small amount of Fe dust in these systems, similar to what is observed in high-z galaxies discovered by the James Webb Space Telescope (JWST). We derive a relationship that allows us to approximate the fraction of Fe trapped into dust in ionized nebulae. If the O-dust scales in the same way, its possible contribution in low-metallicity nebulae would be negligible. After analyzing the Fe/O abundances in J0811+4730 and J1631+4426, we do not see evidence of the presence of very massive stars with Minit > 300 M⊙ in these systems. Conclusions. The close relation observed between the N and Fe abundances has the potential to serve as a link between stellar and nebular chemical studies. This requires an expansion of the number of abundance determinations for these elements in both stars and star-forming nebulae, especially at low metallicities. [ABSTRACT FROM AUTHOR]

We investigated the effect of time-dependent ice growth on dust grains on the opacity and hence on the dust temperature in a collapsing molecular cloud core, with the aim of quantifying the effect of the dust temperature variations on ice abundances as well as the evolution of the collapse. To perform the simulations, we employed a one-dimensional collapse model that self-consistently and time-dependently combines hydrodynamics with chemical and radiative transfer simulations. The dust opacity was updated on the fly based on the ice growth as a function of the location in the core. The results of the fully dynamical model were compared against simulations run with different values of fixed ice thickness. We found that the ice thickness increases quickly and reaches a saturation value (as a result of a balance between adsorption and desorption) of approximately 90 monolayers in the central core (volume density ~104 cm−3), and several tens of monolayers at a volume density of ~103 cm−3, after only a few 105 yr of evolution. The results thus exclude the adoption of thin (approximately ten monolayer) ices in molecular cloud simulations except at very short timescales. However, the differences in abundances and the dust temperature between the fully dynamic simulation and those with a fixed dust opacity are small; abundances change between the solutions generally within a factor of two only. The assumptions on the dust opacity do have an effect on the collapse dynamics through the influence of the photoelectric effect on the gas temperature, and the simulations take a different time to reach a common central density. This effect is, however, small as well. In conclusion, carrying out chemical simulations using a dust temperature corresponding to a fixed opacity seems to be a good approximation. Still, although at least in the present case its effect on the overall results is limited – as long as the grains are monodisperse – ice growth should be considered to obtain the most accurate representation of the collapse dynamics. We have found in a previous work that considering a grain size distribution leads to a complicated ice composition that depends on the grain size nonlinearly. With this in mind, we will carry out a follow-up study where the influence of the grain size on the present simulation setup is investigated. [ABSTRACT FROM AUTHOR]

Context. Analysis of several spectroscopic surveys indicates the presence of a bimodality between the disc stars in the abundance ratio space of [α/Fe] versus [Fe/H]. The two stellar groups are commonly referred to as the high-α and low-α sequences. Some models capable of reproducing such a bimodality invoke the presence of a hiatus in the star formation history in our Galaxy, whereas other models explain the two sequences by means of stellar migration. Aims. Our aim is to show that the existence of the gap in the star formation rate between high-α and low-α is evident in the stars of APOGEE DR17, if one plots [Fe/α] versus [α/H], confirming previous suggestions. We then try to interpret the data by means of detailed chemical models. Methods. We compare the APOGEE DR17 red giant stars with the predictions of a detailed chemical evolution model based on the two-infall paradigm, taking into account also the possible accretion of dwarf satellites. Results. The APOGEE DR17 abundance ratios [Fe/α] versus [α/H] exhibit a sharp increase in [Fe/α] at a nearly constant [α/H] (where α elements considered are Mg, Si, O) during the transition between the two disc phases. This observation strongly supports the hypothesis that a hiatus in star formation occurred during this evolutionary phase. Notably, the most pronounced growth in the [Fe/α] versus [α/H] relation is observed for oxygen, as this element is exclusively synthesised in core-collapse supernovae. The revised version of the two-infall chemical evolution model proposed in this study reproduces the APOGEE DR17 abundance ratios better than before. Particularly noteworthy is the model's ability to predict the hiatus in the star formation between the two infalls of gas, which form the thick and thin disc, respectively, and thus generate abundance ratios compatible with APOGEE DR17 data. Conclusions. We show that the signature of a hiatus in the star formation is imprinted in the APOGEE DR17 abundance ratios. A chemical model predicting a pause in the star formation of a duration of roughly 3.5 Gyr, and in which the high-α disc starts forming from pre-enriched gas by a previous encounter with a dwarf galaxy, could well explain the observations [ABSTRACT FROM AUTHOR]

Context. A rich inventory of complex organic molecules (COMs) has been observed in high abundances in the gas phase toward Class 0 protostars. It has been suggested that these molecules are formed in ices and sublimate in the warm inner envelope close to the protostar. However, only the most abundant COM, methanol (CH3OH), had been firmly detected in ices before the era of the James Webb Space Telescope (JWST). Now, it is possible to detect the interstellar ices of other COMs and constrain their ice column densities quantitatively. Aims. We aim to determine the column densities of several oxygen-bearing COMs (O-COMs) in both gas and ice for two low-mass protostellar sources, NGC 1333 IRAS 2A (hereafter IRAS 2A) and B1-c, as case studies in our JWST Observations of Young proto-Stars (JOYS+) program. By comparing the column density ratios with respect to CH3OH between both phases measured in the same sources, we can probe the evolution of COMs from ice to gas in the early stages of star formation. Methods. The column densities of COMs in gas and ice were derived by fitting the spectra observed by the Atacama Large Millimeter/submillimeter Array (ALMA) and the JWST/Mid-InfraRed Instrument-Medium Resolution Spectroscopy (MIRI-MRS), respectively. The gas-phase emission lines were fit using local thermal equilibrium models, and the ice absorption bands were fit by matching the infrared spectra measured in laboratories. The column density ratios of four O-COMs (CH3CHO, C2H5OH, CH3OCH3, and CH3OCHO) with respect to CH3OH were compared between ice and gas in IRAS 2A and B1-c. Results. We were able to fit the fingerprint range of COM ices between 6.8 and 8.8 μm in the JWST/MIRI-MRS spectra of B1-c using similar components to the ones recently used for NGC 1333 IRAS 2A. We claim detection of CH4, OCN−, HCOO−, HCOOH, CH3CHO, C2H5OH, CH3OCH3, CH3OCHO, and CH3COCH3 in B1-c, and upper limits have been estimated for SO2, CH3COOH, and CH3CN. The total abundance of O-COM ices is constrained to be 15% with respect to H2O ice, 80% of which is dominated by CH3OH. The comparison of O-COM ratios with respect to CH3OH between ice and gas shows two different cases. On the one hand, the column density ratios of CH3OCHO and CH3OCH3 match well between the two phases, which may be attributed to a direct inheritance from ice to gas or strong chemical links with CH3OH. On the other hand, the ice ratios of CH3CHO and C2H5OH with respect to CH3OH are higher than the gas ratios by 1–2 orders of magnitude. This difference can be explained by gas-phase reprocessing following sublimation, or different spatial distributions of COMs in the envelope, which is an observational effect resulting from ALMA and JWST tracing different components in a protostellar system. Conclusions. The firm detection of COM ices other than CH3OH is reported in another well-studied low-mass protostar, B1-c, following the recent detection in NGC 1333 IRAS 2A. The column density ratios of four O-COMs with respect to CH3OH show both similarities and differences between gas and ice. Although the straightforward explanations would be the direct inheritance from ice to gas and the gas-phase reprocessing, respectively, other possibilities such as different spatial distributions of molecules cannot be excluded. [ABSTRACT FROM AUTHOR]

Context. The cosmic-ray ionization rate (ζ2) is one of the key parameters in star formation, since it regulates the chemical and dynamical evolution of molecular clouds by ionizing molecules and determining the coupling between the magnetic field and gas. Aims. However, measurements of ζ2 in dense clouds (e.g., nH ≥ 104 cm−3) are difficult and sensitive to the model assumptions. The aim is to find a convenient analytic approach that can be used in high-mass star-forming regions (HMSFRs), especially for warm gas environments such as hot molecular cores (HMCs). Methods. We propose a new analytic approach to calculate ζ2 through HCO+, N2H+, and CO measurements. By comparing our method with various astrochemical models and with observations found in the literature, we identify the parameter space for which the analytic approach is applicable. Results. Our method gives a good approximation, to within 50%, of ζ2 in dense and warm gas (e.g., nH ≥ 104 cm−3, T = 50, 100 K) for AV ≥ 4 mag and t ≥ 2 × 104 yr at Solar metallicity. The analytic approach gives better results for higher densities. However, it starts to underestimate ζ2 at low metallicity (Z = 0.1 Z⊙) when the value is too high (ζ2 ≥ 3 × 10−15 s−1). By applying our method to the OMC-2 FIR4 envelope and the L1157-B1 shock region, we find ζ2 values of (1.0 ± 0.3) × 10−14 s−1 and (2.2 ± 0.4) × 10−16 s−1, consistent with those previously reported. Conclusions. We calculate ζ2 toward a total of 82 samples in HMSFRs, finding that the average value of ζ2 toward all HMC samples (ζ2 = (7.4±5.0)×10−16 s−1) is more than an order of magnitude higher than the theoretical prediction of cosmic-ray attenuation models, favoring the scenario that locally accelerated cosmic rays in embedded protostars should be responsible for the observed high ζ2. [ABSTRACT FROM AUTHOR]

We quantified the disparity between gas-phase and stellar metallicity in a large galaxy sample obtained from the MaNGA DR17 survey. We found that the gas metallicity is on average closely aligned with the stellar metallicity in the centers of intermediate-mass galaxies. Conversely, the difference is notably larger within the center of massive galaxies. It reaches about −0.18 dex on average for the most massive galaxies, while for low-mass galaxies, the gas metallicity exhibits a slightly lower value than the stellar metallicity. Moreover, the most prominent instances of a reduced gas-phase metallicity in relation to stellar metallicity were observed within the centers of massive red galaxies with low specific star formation rates. Because of the absence of a correlation between the integral mass fraction of neutral gas and the disparity between gas and stellar metallicity, we suggest that the diminished gas-phase metallicity in the centers of massive galaxies might be attributed to the replenishment of gas-depleted central regions through processes such as radial gas flows or accretion from the circumgalactic medium rather than gas infall from the intergalactic medium. [ABSTRACT FROM AUTHOR]

We present a search for galaxies in the local Universe with extremely low oxygen abundance, that is, more than 25 times lower than solar, which corresponds to 12 + log(O/H) < 7.3. To determine the oxygen abundance, we apply the direct Te method for objects where the [O III]λ4363 line is detected. We identified 21 extremely metal-poor galaxies in the early data release of the Dark Energy Spectroscopic Instrument (DESI EDR), for some of which we also derived N/O, Ne/O, Ar/O, and S/O ratios. We find that many DESI galaxies with extremely low oxygen abundance exhibit a higher N/O ratio in comparison to the reference low-metallicity sample collected from the literature. We suggest that the elevation in N/O ratio may be explained by a contamination with metal-rich gas caused by gas inflow or a merger event. Moreover, contrary to some recent studies, we find that Ar/O and S/O ratios are enhanced as well, while the Ne/O ratio does not show such elevation. One of the galaxies, J0713+5608, has a remarkably low oxygen abundance of 6.978 ± 0.095 dex. This measurement aligns with the lowest known oxygen abundances in galaxies to date. Given the relatively high uncertainty, this galaxy may have the lowest oxygen abundance ever found. Additionally, J0713+5608 exhibited an enhanced N/O ratio compared to the typical N/O ratio observed in metal-poor galaxies within the local Universe. [ABSTRACT FROM AUTHOR]

Aims. The line of sight toward Sk 143 (AzV 456), an O9.5 Ib star in the Small Magellanic Cloud (SMC), shows significant absorption from neutral atoms and molecules. We report a new study of this line of sight by means of high-resolution spectra obtained with the ESPRESSO spectrograph at the VLT of ESO. Methods. The absorption from neutral and ionized species is well characterized by a single component at vhel ≈ +132 km s−1 that was modeled with the ASTROCOOK code. Results. The rubidium Rb I 780.0 nm line is detected for the first time outside the Galaxy, and we derive [Rb/H] = −1.86 ± 0.09. As a result of the high resolution, the 85Rb and 87Rb isotope lines are also exceptionally well resolved. The 85Rb/87Rb isotope ratio is 0.46, which is opposite of the meteoritic value of 2.43. This implies that Rb is made through a dominant contribution of the r-process, which is dominant for the 87Rb isotope. We also confirm the presence of 7Li I 670.7 nm and set a limit on the isotopic ratio of 6Li/7Li < 0.1. Conclusions. The dominance of the 87Rb isotope implies that Rb is made through a dominant contribution of the r-process. At the low metallicity of the cloud of [Zn/H] = −1.28 ± 0.09, neutron rich material may have occurred in rotating metal-poor massive stars. Moreover, the low metallicity of the cloud leads to an absolute Li abundance of A(7Li) ≈ 2.2, which differs from the expectation from big bang nucleosynthesis. Because the gas-phase abundance is not affected by stellar depletion, the burning of Li inside the halo stars is probably not the solution for the cosmological 7Li problem. [ABSTRACT FROM AUTHOR]

SN 2021adxl is a slowly evolving, luminous, Type IIn supernova with asymmetric emission line profiles, similar to the well-studied SN 2010jl. We present extensive optical, near-ultraviolet, and near-infrared photometry and spectroscopy covering ∼1.5 years post discovery. SN 2021adxl occurred in an unusual environment, atop a vigorously star-forming region that is offset from its host galaxy core. The appearance of Lyα and O II, as well as the compact core, would classify the host of SN 2021adxl as a "Blueberry" galaxy, analogous to higher redshift, low-metallicity, star-forming dwarf "Green Pea" galaxies. Using several abundance indicators, we find a metallicity of the explosion environment of only ∼0.1 Z⊙, the lowest reported metallicity for a Type IIn SN environment. SN 2021adxl reaches a peak magnitude of Mr ≈ −20.2 mag and since discovery, SN 2021adxl has faded by only ∼4 magnitudes in the r band with a cumulative radiated energy of ∼1.5 × 1050 erg over 18 months. SN 2021adxl shows strong signs of interaction with a complex circumstellar medium, seen by the detection of X-rays, revealed by the detection of coronal emission lines, and through multi-component hydrogen and helium profiles. In order to further understand this interaction, we model the Hα profile using a Monte Carlo electron scattering code. The blueshifted high-velocity component is consistent with emission from a radially thin spherical shell resulting in the broad emission components due to electron scattering. Using the velocity evolution of this emitting shell, we find that the SN ejecta collide with circumstellar material of at least ∼5 M⊙ assuming a steady-state mass-loss rate of ∼4 − 6 × 10−3 M⊙ yr−1 for the first ∼200 days of evolution. SN 2021adxl was last observed to be slowly declining at ∼0.01 mag d−1, and if this trend continues, SN 2021adxl will remain observable after its current solar conjunction. Continuing the observations of SN 2021adxl may reveal signatures of dust formation or an infrared excess, similar to that seen for SN 2010jl. [ABSTRACT FROM AUTHOR]

Detection of the AlCl molecule in IRC+10216 has been reported in the literature. We here report calculations of reaction rate constants for formation of AlCl through radiative association of Al and Cl for a temperature interval of 1000 to 14000 K. Potential energy and permanent/transition dipole moment curves were taken from the literature. Quantum mechanical and semiclassical/classical methods were used to obtain the reaction cross-sections and thermal rate constants, accounting for shape resonances with Breit–Wigner theory. Both the A |$^1 \Pi \rightarrow$| X |$^1 \Sigma ^+$| transition and the X |$^1 \Sigma ^+\rightarrow$| X |$^1 \Sigma ^+$| transition have been treated, with results showing that the former dominates for the temperatures considered in this study. Our rate constants are a factor of two to three larger than previously calculated values, where the latter were obtained without considering resonances or the X |$^1 \Sigma ^+\rightarrow$| X |$^1 \Sigma ^+$| transition. Our new values do however not change the previous conclusion that radiative association can only contribute modestly to the formation of AlCl under the given conditions. [ABSTRACT FROM AUTHOR]

The propargyl cation, H2CCCH+, is a crucial hydrocarbon precursor in the chemical evolution of the interstellar medium (ISM). It serves as a key intermediate for understanding ISM hydrocarbon chemistry. This work presents state-to-state collisional rate coefficients for rotational excitation and de-excitation of ortho- and para- H2CCCH+ colliding with He at ISM-relevant temperatures (T  ≤ 60 K). We employed a high-level post-Hartree-Fock CCSD(T)-F12/aug-cc-pVTZ method to generate a 3D interaction potential energy surface (3D-PES) for the weakly bound H2CCCH+-He complex. The analytical 3D-PES was then used in close-coupling calculations to determine cross-sections for rotational excitation and de-excitation of ortho- and para- H2CCCH+ by collisions with He for kinetic energies (Ek) up to 300 cm−1. Inelastic collision rate coefficients were subsequently obtained by thermally averaging the cross-sections over a Maxwell–Boltzmann distribution of kinetic energies. Our results indicate that at very low temperatures (T  < 15 K), rotational transitions associated with Δj = Δkc = ±1, which are crucial for the identification of H2CCCH+ in astronomical surveys, exhibit the largest cross-sections. In contrast, at higher temperatures, transitions with Δj = Δkc = ±2 become more dominant. These data hold significant implications for the determination of the H2CCCH+ abundance in the ISM and improve the modelling of interstellar hydrocarbon-chain reaction pathways. [ABSTRACT FROM AUTHOR]

For the first time, a calibration between the He  i |$\lambda 5876$| /H  |$\beta$| emission line ratio and the helium abundance y = 12 + log(He/H) for Narrow line regions of Seyfert 2 Active Galactic Nuclei is proposed. In this context, observational data (taken from the SDSS-DR15 and from the literature) and direct abundance estimates (via the |$T_{\rm e}$| -method) for a sample of 65 local (⁠|$z \: \lt \: 0.2$|⁠) Seyfert 2 nuclei are considered. The resulting calibration estimates the y abundance with an average uncertainty of 0.02 dex. Applying our calibration to spectroscopic data containing only strong emission lines, it yields a helium abundance distribution similar to that obtained via the |$T_{\rm e}$| -method. Some cautions must be considered to apply our calibration for Seyfert 2 nuclei with high values of electron temperature (⁠|${\gtrsim} 20\, 000$|  K) or ionization parameter (⁠|$\log U \ \gt\ {-}2.0$|⁠). [ABSTRACT FROM AUTHOR]

The identification of complex pre-biotic molecules using millimetre and submillimetre telescopes allows us to understand how the basic building blocks of life are formed in the universe. In the interstellar medium, ethylene glycol (⁠|$({\rm CH}_2{\rm OH})_{2}$|⁠) is the simplest sugar alcohol molecule, and it is the reduced alcohol of the simplest sugar-like molecule, glycolaldehyde (⁠|${\rm CH}_{2}{\rm OHCHO}$|⁠). We present the detection of the rotational emission lines of |$aGg^{\prime }$| conformer of ethylene glycol (⁠|$({\rm CH}_2{\rm OH})_{2}$|⁠) towards the hot molecular core G358.93–0.03 MM1 using the Atacama Large Millimeter/Submillimeter Array. The estimated column density of |$aGg^{\prime }$| - |$({\rm CH}_2{\rm OH})_{2}$| towards the G358.93–0.03 MM1 is (4.5 |$\pm 0.1)\times 10^{16}$| cm |$^{-2}$| with an excitation temperature of 155 |$\pm$| 35 K. The abundance of |$aGg^{\prime }$| - |$({\rm CH}_2{\rm OH})_{2}$| with respect to |${\rm H}_{2}$| is (1.4 |$\pm 0.5)\times 10^{-8}$|⁠. Similarly, the abundances of |$aGg^{\prime }$| - |$({\rm CH}_2{\rm OH})_{2}$| with respect to |${\rm CH}_{2}{\rm OHCHO}$| and |${\rm CH}_{3}{\rm OH}$| are 3.1 |$\pm$| 0.5 and (6.1 |$\pm 0.3)\times 10^{-3}$|⁠. We compare the estimated abundance of |$aGg^{\prime }$| - |$({\rm CH}_2{\rm OH})_{2}$| with the existing three-phase warm-up chemical model abundance of |$({\rm CH}_2{\rm OH})_{2}$|⁠ , and we notice the observed abundance and modelled abundance are nearly similar. We discuss the possible formation pathways of |$aGg^{\prime }$| - |$({\rm CH}_2{\rm OH})_{2}$| towards the hot molecular cores, and we find that |$aGg^{\prime }$| - |$({\rm CH}_2{\rm OH})_{2}$| is probably created via the recombination of two |${\rm CH}_{2}{\rm OH}$| radicals on the grain surface of G358.93–0.03 MM1. [ABSTRACT FROM AUTHOR]

Aims. We present a new sub-grid model, HYACINTH – HYdrogen And Carbon chemistry in the INTerstellar medium in Hydro simulations – for computing the non-equilibrium abundances of H2 and its carbon-based tracers, namely CO, C, and C+, in cosmological simulations of galaxy formation. Methods. The model accounts for the unresolved density structure in simulations using a variable probability distribution function of sub-grid densities and a temperature-density relation. Included is a simplified chemical network that has been tailored for hydrogen and carbon chemistry within molecular clouds and easily integrated into large-scale simulations with minimal computational overhead. As an example, we applied HYACINTH to a simulated galaxy at redshift z ~ 2.5 in post-processing and compared the resulting abundances with observations. Results. The chemical predictions from HYACINTH are in reasonable agreement with high-resolution molecular-cloud simulations at different metallicities. By post-processing a galaxy simulation with HYACINTH, we reproduced the H I − H2 transition as a function of the hydrogen column density NH for both Milky-Way-like and Large-Magellanic-Cloud-like conditions. We also matched the NCO versus NH2 relation inferred from absorption measurements towards Milky-Way molecular clouds, although most of our post-processed regions occupy the same region as (optically) dark molecular clouds in the NCO – NH2 plane. Column density maps reveal that CO is concentrated in the peaks of the H2 distribution, while atomic carbon more broadly traces the bulk of H2 in our post-processed galaxy. Based on both the column density maps and the surface density profiles oŕ the different gas species in the post-processed galaxy, we find that C+ maintains a substantially high surŕace density out to ~10 kpc as opposed to other components that exhibit a higher central concentration. This is similar to the extended [C II] emission ŕound in some recent observations at high redshifts. [ABSTRACT FROM AUTHOR]

In recent years, the study of the Milky Way has significantly advanced due to extensive spectroscopic surveys of its stars, complemented by astroseismic and astrometric data. However, it remains disjoint from recent advancements in understanding the physics of the Galactic interstellar medium (ISM). This paper introduces a new model for the chemical evolution of the Milky Way that can be constrained on stellar data, because it combines a state-of-the-art ISM model with a Milky Way stellar disc model. Utilizing a data set of red clump stars from APOGEE, known for their precise ages and metallicities, we concentrate on the last 6 billion years – a period marked by Milky Way's secular evolution. We examine the oxygen abundance in the low- |$\alpha$| disc stars relative to their ages and birth radii, validating or constraining critical ISM parameters that remain largely unexplored in extragalactic observations. The models that successfully reproduce the radius–metallicity distribution and the age–metallicity distribution of stars without violating existing ISM observations indicate a need for modest differential oxygen enrichment in Galactic outflows, meaning that the oxygen abundance of outflows is higher than the local ISM abundance, irrespective of outflow mass loading. The models also suggest somewhat elevated ISM gas velocity dispersion levels over the past 6 billion years compared to galaxies of similar mass. The extra turbulence necessary could result from energy from gas accretion onto the Galaxy, supernovae clustering in the ISM, or increased star formation efficiency per freefall time. This work provides a novel approach to constraining the Galactic ISM and outflows, leveraging the detailed insights available from contemporary Milky Way surveys. [ABSTRACT FROM AUTHOR]

Context. The metallicity distribution function (MDF) of the Galactic bulge is characterized by a multi-peak shape, with a metal-poor peak centered at [Fe/H] ∼ −0.3 dex and a metal-rich peak centered at [Fe/H] ∼ +0.3 dex. The bimodality of the MDF is also reflected in the [α/Fe] versus [Fe/H] abundance ratios, suggesting the presence of different stellar populations in the bulge. Aims. In this work we aim to reproduce the observed MDF of the Galactic bulge by testing a scenario in which the metal-poor component of the bulge is formed by stars formed in situ, during a strong burst of star formation, while the metal-rich population is formed by stars created in situ during a second burst of star formation and/or stars accreted from the innermost part of the Galactic disk as an effect of a growing bar. Methods. We adopted a chemical evolution model that is able to follow the evolution of several chemical species with detailed nucleosynthesis prescriptions. In particular, because of the importance of the production of Fe in constraining the MDF, close attention is paid to the production of this element in both Type Ia supernovae and massive stars. In particular, we included yields from rotating massive stars with different rotational velocity prescriptions. Our model also takes the infall and outflow of gas into account, as well as the effect of stellar migration. Results are compared to ∼13 000 stars from the SDSS/APOGEE survey that belong to the region located at a Galactocentric distance RGC ≤ 3.5 kpc. Results. We successfully reproduce the observed double-peak shape of the bulge MDF as well as the abundance trends of the α elements relative to Fe by assuming both (i) a multi-burst star formation history with a quenching of the first burst of ∼102 Myr and (ii) migration of stars from the innermost part of the Milky Way disk, as an effect of a growing bar. According to our results, the fraction of the stellar mass of the bulge-bar that belongs to the inner disk is ∼40%. In terms of the nucleosynthesis, we conclude that models that assume either no rotation for massive stars or a distribution of rotational velocities that favors slow rotation at high metallicities best reproduce the observed MDF as well as the [α/Fe] and the [Ce/Fe] versus [Fe/H] abundance patterns. [ABSTRACT FROM AUTHOR]

Context. The carbamoyl radical (H2NCO) is believed to play a central role in the ice-grain chemistry of crucial interstellar complex organic molecules such as formamide and acetamide. Yet, little is known about this radical, which remains elusive in laboratory gasphase experiments. Aims. In order to enable interstellar searches of H2NCO, we have undertaken a mandatory laboratory characterisation of its pure rotational spectrum. Methods. We report the gas-phase laboratory detection of H2NCO, produced by H-atom abstraction from formamide, using pure rotational spectroscopy at millimetre and submillimetre wavelengths. Millimetre-wave data were acquired using chirped-pulse Fourier-transform spectroscopy, while submillimetre-wave ones were obtained using Zeeman-modulated spectroscopy. Experimental measurements were guided by quantum-chemical calculations at the ωB97X-D/cc-pVQZ level of theory. Interstellar searches for the radical have been undertaken in the Protostellar Interferometric Line Survey (PILS) towards the solar-type protostar IRAS 16293-2422. Results. From the assignment and fit of experimental transitions up to 660 GHz, reliable spectroscopic parameters for H2NCO in its ground vibrational state have been derived, enabling accurate spectral predictions. No transitions of the radical were detected in the PILS survey. The inferred upper limit shows that the H2NCO abundance is at least 60 times below that of formamide and 160 times below that of HNCO in this source; a value that is in agreement with predictions from a physico-chemical model of this young protostar. [ABSTRACT FROM AUTHOR]

Context. One of the main problems in astrochemistry is determining the amount of sulfur in volatiles and refractories in the interstellar medium. The detection of the main sulfur reservoirs (icy H2S and atomic gas) has been challenging, and estimates are based on the reliability of models to account for the abundances of species containing less than 1% of the total sulfur. The high sensitivity of the James Webb Space Telescope provides an unprecedented opportunity to estimate the sulfur abundance through the observation of the [S I] 25.249 µm line. Aims. Our aim is to determine the amount of sulfur in the ionized and warm molecular phases toward the Orion Bar as a template to investigate sulfur depletion in the transition between the ionized gas and the molecular cloud in HII regions. Methods. We used the [S III] 18.7 µm, [S IV] 10.5 µm, and [S l] 25.249 µm lines to estimate the amount of sulfur in the ionized and molecular gas along the Orion Bar. For the theoretical part, we used an upgraded version of the Meudon photodissociation region (PDR) code to model the observations. New inelastic collision rates of neutral atomic sulfur with ortho-and para- molecular hydrogen were calculated to predict the line intensities. Results. The [S III] 18.7 µm and [S IV] 10.5 µm lines are detected over the imaged region with a shallow increase (by a factor of 4) toward the HII region. This suggests that their emissions are partially coming from the Orion Veil. We estimate a moderate sulfur depletion, by a factor of ~2, in the ionized gas. The corrugated interface between the molecular and atomic phases gives rise to several edge-on dissociation fronts we refer to as DF1, DF2, and DF3. The [S l] 25.249 µm line is only detected toward DF2 and DF3, the dissociation fronts located farthest from the HII region. This is the first ever detection of the [S l] 25.249 µm line in a PDR. The detailed modeling of DF3 using the Meudon PDR code shows that the emission of the [S l] 25.249 µm line is coming from warm (>40 K) molecular gas located at AV ~1–5 mag from the ionization front. Moreover, the intensity of the [S l] 25.249 µm line is only accounted for if we assume the presence of undepleted sulfur. Conclusions. Our data show that sulfur remains undepleted along the ionic, atomic, and molecular gas in the Orion Bar. This is consistent with recent findings that suggest that sulfur depletion is low in massive star-forming regions because of the interaction of the UV photons coming from the newly formed stars with the interstellar matter. [ABSTRACT FROM AUTHOR]

Context. Carbon is the fourth most abundant element in the universe and its distribution is critical to understanding stellar evolution and nucleosynthesis. In optical studies of ionized nebulae, the only way to determine the C/H abundance is by using faint C II recombination lines (RLs). However, these lines give systematically higher abundances than their collisionally excited counterparts, observable at ultraviolet (UV) wavelengths. Therefore, a proper understanding of the excitation mechanisms of the faint permitted lines is crucial for addressing this long-standing abundance discrepancy (AD) problem. Aims. In this study, we investigate the excitation mechanisms of C II lines λλ3918, 3920, 4267, 5342, 6151, 6462, 7231, 7236, 7237, and 9903. Methods. We use the DEep Spectra of Ionized REgions Database (DESIRED) that contains spectra of H II regions, planetary nebulae and other objects to analyze the fluorescence contributions to these lines and the accuracy of the atomic recombination data used to model the C+ ion. Results. We find that C IIλλ4267, 5342, 6151, 6462, and 9903 arise exclusively from recombinations with no fluorescent contributions. In addition, the recombination theory for these lines is consistent with the observations. Our findings show that the AD problem for C2+ is not due to fluorescence in the widely used C II lines or errors in their atomic parameters, but to other phenomena such as temperature variations or chemical inhomogeneities. On the other hand, C IIλλ3918, 3920, 6578, 7231, 7236, 7237 have important fluorescent contributions, which are inadvisable for tracing the C2+ abundances. We also discuss the effects of possible inconsistencies in the atomic effective recombination coefficients of C IIλλ6578, 7231, 7236, and 7237. [ABSTRACT FROM AUTHOR]

Context. Compact groups of galaxies are unique places where galaxy-galaxy interactions play a mayor role on the evolution of its members. These strong gravitational encounters can induce star formation bursts. Aims. We study the properties of one of the most luminous so-called hinge clumps that is located in the compact group of galaxies NGC 6845. Methods. Using integral field spectroscopy from GMOS/Gemini complemented with archival MUSE data, we obtained oxygen abundances, ages, star formation rates, and velocity fields, and we also modeled a single stellar population to understand the star formation history of the hinge clump in NGC 6845. Results. We found that the hinge clump sits in a tailthat has a star formation rate of 3.4 M⊙ yr−1, which is comparable with a few other extreme cases, for instance, the star clusters in the Antennae galaxy and other reported hinge clumps in the literature. This clump represents ∼15% of total star formation rate of NGC 6845A. Large-scale modeling of the observed velocity field of NGC 6845A rules out the scenario according to which this hinge clump was a satellite galaxy. Its kinematics is compatible with that of the galactic disk of NGC 6845A. Its abundance with a mean value of 0.4 Z⊙ is also consistent with the metallicity gradient of the galaxy. Conclusions. Our analysis suggest that the hinge clump is formed by multiple stellar populations and not by a single burst. This causes the wide age range. We found that the central clump is encompassed by a ring-like structure, which might suggest a second generation of star formation. In addition, the analysis of the diagnostic diagram indicates that this central region might also be ionized by shocks from stellar and supernova winds. Finally, the derived star formation rate density Σ = 9.7 M⊙ yr−1 kpc−2 of the central clump places it in starburst regime, where gas inflows should provide gas to maintain the star formation. This work shows a resolved example of an extreme localized starburst in a compact group of galaxies. [ABSTRACT FROM AUTHOR]

Context. The Small Magellanic Cloud (SMC) is an ideal laboratory for studying the properties of star-forming regions thanks to its low metallicity, which has an impact on the molecular gas abundance. However, a small number of molecular gas surveys of the entire galaxy have been carried out in the last few years, limiting the measurements of interstellar medium (ISM) properties in a homogeneous manner. Aims. We present the CO(3-2) APEX survey at a 6 pc resolution of the bar of the SMC, observed with the SuperCAM receiver attached to the APEX telescope. This high-resolution survey has allowed us to study certain properties of the ISM and to identify CO clouds in the innermost parts of the H2 envelopes. Methods. We adopted the CO analysis in the SMC bar comparing the CO(3–2) survey with that of the CO(2–1) of a similar resolution. We studied the CO(3–2)-to-CO(2–1) ratio (R32), which is very sensitive to the environment properties (e.g., star-forming regions). We analyzed the correlation of this ratio with observational quantities that trace the star formation such as the local CO emission, the Spitzer color [70/160], and the total IR surface brightness measured from the Spitzer and Herschel bands. For the identification of the CO(3–2) clouds, we used the CPROPS algorithm, which allowed us to measure the physical properties of the clouds. We analyzed the scaling relationships of such physical properties. Results. We obtained R32 = 0.65 ± 0.02 for the SW bar and a slightly higher ratio, R32 = 0.7 ± 0.1, for N66 in the SMC. We found that R32 varies from region to region, depending on the star formation activity. In regions dominated by HII and photo-dissociated regions (e.g., N22, N66) R32 tends to be higher than the median values. Meanwhile, lower values were found toward quiescent clouds. We also found that R32 is correlated with the IR color [70/160] and the total IR surface brightness. This finding indicates that R32 increases with environmental properties, such as the dust temperature, total gas density, and radiation field. We identified 225 molecular clouds with sizes of R > 1.5 pc and signal-to-noise ratios (S/N) of >3, of which only 17 are well resolved CO(3–2) clouds with S/N ≳ 5. These 17 clouds follow consistent scaling relationships to the inner Milky Way clouds but with some departures. For instance, CO(3–2) tends to be less turbulent and less luminous than the inner Milky Way clouds of similar sizes. Finally, we estimated a median virial-based CO(3–2)-to-H2 conversion factor of 12.6−7+10M⊙ (K km s−1 pc2)−1 for the total sample. [ABSTRACT FROM AUTHOR]

Context. Among the silicon-bearing species discovered in the interstellar medium, SiS and SiO stand out as key tracers due to their distinct chemistry and variable abundances in interstellar and circumstellar environments. Nevertheless, while the origins of SiO are well documented, the SiS chemistry remains relatively unexplored. Aims. Our objective is to enhance the network of Si- and S-bearing chemical reactions for a gas-grain model in molecular clouds, encompassing both low and high metallicities. To achieve this, we calculated the energies and rate coefficients for six neutral atom-diatom reactions involved in the SiCS triatomic system, with a special focus on the C+SiS and S+SiC collisions. Methods. We employed the coupled-cluster method with single and double substitutions and a perturbative treatment of triple substitutions (CCSD(T)) refined at the explicitly correlated CCSD(T)-F12 level. With these computational results in conjunction with supplementary data from the literature, we construct an extended network of neutral-neutral chemical reactions involving Si- and S-bearing molecules. To assess the impact of these chemical reactions, we performed time-dependent models employing the Nautilus gas-grain code, setting the gas temperature to 10 K and the H2 density to 2 × 104 cm−3. The models considered two initial abundance scenarios, corresponding to low- and high-metallicity levels. Abundances were computed using both the default chemical network and the constrained network, enriched with newly calculated reactions. Results. The temperature dependence for the reactions involving SiS were modelled to the k(T) = α (T/300)β exp (−γ/T) expression, and the coefficients are provided for the first time. The high-metallicity models significantly boost the SiS production, resulting in abundances nearly four orders of magnitude higher compared to low-metallicity models. Higher initial abundances of C, S, and Si, roughly ~2, 190, and 210 times higher, respectively, contribute to this. Around the age of 103 yr, destruction mechanisms become relevant, impacting the abundance of SiS. The proposed production reaction S + SiC → C + SiS, mitigates these effects in later stages. By expanding the gas reaction network using a high-metallicity model, we derived estimates for the abundances of observed interstellar molecules, including SiO, SO, and SO2. Conclusions. We demonstrate the significance of both SiC+S and C+SiS channels in the SiS chemistry. Notably, the inclusion of neutral-neutral mechanisms, particularly via Si+HS and S+SiC channels, played a pivotal role in determining SiS abundance. These mechanisms carry a significance level on a par with that of the well-known and fast ion-neutral reactions. [ABSTRACT FROM AUTHOR]

Context. Complex organic molecules have been observed toward many protostars. Their column density ratios are generally constant across protostellar systems, with some low-level scatter. However, the scatter in the column density ratio of formamide (NH2CHO) to methanol (CH3OH), NNH2CHO/NCH3OH, is one of the highest compared to other ratios. The larger scatter for NNH2CHO/NCH3OH (or weak correlation of these two molecules) is sometimes interpreted as evidence of gas-phase formation of NH2CHO. Aims. In this work, we propose an alternative interpretation in which this scatter is produced by differences in the snowline locations related to differences in binding energies of these species (formamide typically has a ≳2000 K larger binding energy than methanol) and the small-scale structure of the envelope and the disk system. Therefore, we do not include chemistry in our models in order to isolate the effect of physical factors. We also include CH3CN in our work as a control molecule, as it has a similar binding energy to CH3OH. Methods. We used radiative transfer models to calculate the emission from NH2CHO, CH3OH, and CH3CN in protostellar systems with and without disks. The abundances of these species were parameterized in our models, and we fit the calculated emission lines to find the column densities and excitation temperatures of these species, as done in real observations. Results. Given the difference in binding energies of NH2CHO and CH3OH, we find the gas-phase NNH2CHO/NCH3OH needs to be multiplied by a correction factor of approximately ten in order to give the true abundance ratio of these two species in the ices. This factor is much smaller (i.e., ~2) for NCH3CN/NCH3OH (the control molecule). We find that models with different disk sizes, luminosities, and envelope masses produce a scatter in this correction factor, and hence in NNH2CHO/NCH3OH comparable with that of observations. The scatter in NNH2CHO/NCH3OH is larger than that of NCH3CN/NCH3OH in models consistent with the observations. However, the scatter in the models for NCH3CN/NCH3OH is smaller than observations by a factor of around two, as expected from the similar binding energies of CH3OH and CH3CN pointing to the need for some chemical effects in the gas or ice to explain the observed ratios. We show that the scatter in NNH2CHO/NCH3OH will be lower than previously measured if we correct for the difference in sublimation temperatures of these two species in observations of ~40 protostellar systems with ALMA. Conclusions. The scatter in NNH2CHO/NCH3OH (or the ratio of any two molecules with a large binding energy difference) can be partially explained by the difference in their binding energies. Correction for this bias makes the scatter in this ratio similar to that in ratios of other complex organics in the observations, making NH2CHO a "normal" molecule. Therefore, we conclude that gas-phase chemistry routes for NH2CHO are not necessary to explain the larger scatter of NNH2CHO/NCH3OH compared with other ratios. [ABSTRACT FROM AUTHOR]

Astrochemical models are important tools to interpret observations of molecular and atomic species in different environments. However, these models are time-consuming, precluding a thorough exploration of the parameter space, leading to uncertainties and biased results. Using neural networks to simulate the behaviour of astrochemical models is a way to circumvent this problem, providing fast calculations that are based on real astrochemical models. In this paper, we present a fast neural emulator of the astrochemical code Nautilus based on conditional neural fields. The resulting model produces the abundance of 192 species for arbitrary times between 1 and 107 yr. Uncertainties well below 0.2 dex are found for all species, while the computing time is of the order of 104 smaller than Nautilus. This will open up the possibility of performing much more complex forward models to better understand the physical properties of the interstellar medium. As an example of the power of these models, we ran a feature importance analysis on the electron abundance predicted by Nautilus. We found that the electron density is coupled to the initial sulphur abundance in a low-density gas. Increasing the initial sulphur abundance from a depleted scenario to the cosmic abundance leads to an enhancement of an order of magnitude of the electron density. This enhancement can potentially influence the dynamics of the gas in star formation sites. [ABSTRACT FROM AUTHOR]

Despite hydrogen sulphide (H2S) has been predicted to be the major reservoir of S-bearing species on the icy mantles of interstellar grains, no solid H2S has been detected so far. A crucial parameter that governs whether or not a species remains frozen on to the grain mantles is its binding energy (BE). We present a new computational study of the H2S BE on a large amorphous water ice surface, constituted by 200 water molecules. The resulting H2S BE distribution ranges from 57 K (0.5 kJ mol−1) to 2406 K (20.0 kJ mol−1), with the average μ = 984 K (8.2 kJ mol−1). We discuss the reasons why the low bound of the newly computed BE distribution, which testifies to the very weak interaction of H2S with the ice surface, has never been found by previous theoretical or experimental works before. In addition, the low H2S BEs may also explain why frozen H2S is not detected in interstellar ices. Following previous molecular dynamics studies that show that the energy of reactions occurring on ice surfaces is quickly absorbed by the water molecules of the ice and conservatively assuming that 10 per cent of the HS + H → H2S formation energy (−369.5 kJ mol−1) is left to the newly formed H2S, its energy is more than twice the largest BE and five times the average BE and, hence, H2S will most likely leave the water surface. [ABSTRACT FROM AUTHOR]

In this work, we investigated the nitrogen and oxygen abundances in a sample of galaxies with Low Ionization Nuclear Emission Regions (LINERs) in their nucleus. Optical spectroscopic data (3600 – 10 000 Å) of 40 LINERs from the Mapping Nearby Galaxies (MaNGAs) survey were considered. Only objects classified as retired galaxies, that is, whose main ionization sources are post-Asymptotic Giant Branch (pAGB) stars, were selected. The abundance estimates were obtained through detailed photoionization models built with the cloudy code to reproduce a set of observational emission line intensities ratios of the sample. Our results show that LINERs have oxygen and nitrogen abundances in the ranges of |$\rm 8.0 \: \lesssim \: 12+\log (O/H) \: \lesssim \: 9.0$| (mean value 8.74 ± 0.27) and |$\rm 7.6 \: \lesssim \: 12+\log (N/H) \: \lesssim \: 8.5$| (mean value 8.05 ± 0.25), respectively. About 70 per cent of the sample have oversolar O/H and N/H abundances. Our abundance estimates are in consonance with those for Seyfert 2 nuclei and H  ii regions with the highest metallicity, indicating that these distinct object classes show similar enrichment of the interstellar medium (ISM). The LINERs in our sample are located in the higher N/O region of the N/O versus O/H diagram, showing an unexpected negative correlation between these two parameters. These results suggest that these LINERs mainly exhibit a secondary nitrogen production and could be acting some other mechanisms that deviate them from the usual theoretical secondary nitrogen production curve and the H  ii regions observations. However, we did not find any evidence in our data able to support the literature suggested mechanisms. Alternatively, our results show that LINERs do not present any correlation between the N/O abundances and the stellar masses of the hosting galaxies. [ABSTRACT FROM AUTHOR]

The CO-dark molecular gas (DMG), which refers to the molecular gas not traced by CO emission, is crucial for the evolution of the interstellar medium (ISM). While the gas properties of DMG have been widely explored in the Solar neighborhood, whether or not they are similar in the outer disk regions of the Milky Way is still not well understood. In this Letter, we confirm the existence of DMG toward a cold H I arc structure at 13 kpc away from the Galactic center with both OH emission and H I narrow self-absorption (HINSA). This is the first detection of HINSA in the outer disk region, in which the HINSA fraction (NHINSA/NH2 = 0.022 ± 0.011) is an order of magnitude higher than the average value observed in nearby evolved dark clouds, but is consistent with that of the early evolutionary stage of dark clouds. The inferred H2 column density from both extinction and OH emission (NH2 ≈ 1020 cm−2) is an order of magnitude higher than previously estimated. Although the ISM environmental parameters are expected to be different between the outer Galactic disk regions and the Solar neighborhood, we find that the visual extinction (AV = 0.19 ± 0.03 mag), H2-gas density (nH2 = 91 ± 46 cm−3), and molecular fraction (58% ± 28%) of the DMG are rather similar to those of nearby diffuse molecular clouds. The existence of DMG associated with the expanding H I supershell supports a scenario where the expansion of supershells may trigger the formation of molecular clouds within a crossing timescale of the shock wave (∼106 yr). [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Impact of nonconvergence and various approximations of the partition function on the molecular column densities in the interstellar medium." The full text of the article is not available in HTML format. The authors acknowledge the contributions of Dr. Edgar Mendoza and the funding received from the European Union's Horizon 2020 research and innovation program. The authors of the article are M. Carvajal, C. Favre, I. Kleiner, C. Ceccarelli, E. A. Bergin, and D. Fedele. [Extracted from the article]

Context. Nitrogen fractionation is a powerful tracer of the chemical evolution during star and planet formation. It requires robust determinations of the nitrogen fractionation across different evolutionary stages. Aims. We aim to determine the 14N/15N and 12C/13C ratios for HCN in six starless and prestellar cores and to compare the results between the direct method using radiative transfer modeling and the indirect double isotope method, assuming a fixed 12C/13C ratio. Methods. We present IRAM observations of the HCN 1–0, HCN 3–2, HC15N 1–0 and H13CN 1–0 transitions toward six embedded cores. The 14N/15N ratio was derived using both the indirect double isotope method and directly through non-local thermodynamic equilibrium (NLTE) 1D radiative transfer modeling of the HCN emission. The latter also provides the 12C/13C ratio, which we compared to the local interstellar value. Results. The derived 14N/15N ratios using the indirect method are generally in the range of 300-550. This result could suggest an evolutionary trend in the nitrogen fractionation of HCN between starless cores and later stages of the star formation process. However, the direct method reveals lower fractionation ratios of around ~250, mainly resulting from a lower 12C/13C ratio in the range ~20–40, as compared to the local interstellar medium value of 68. Conclusions. This study reveals a significant difference between the nitrogen fractionation ratio in HCN derived using direct and indirect methods. This can influence the interpretation of the chemical evolution and reveal the pitfalls of the indirect double isotope method for fractionation studies. However, the direct method is challenging, as it requires well-constrained source models to produce accurate results. No trend in the nitrogen fractionation of HCN between earlier and later stages of the star formation process is evident when the results of the direct method are considered. [ABSTRACT FROM AUTHOR]

Context. Thermal diffusion is one of the basic processes for the mobility and formation of species on cosmic dust grains. The rate of thermal diffusion is determined by the grain surface temperature, a pre-exponential factor, and an activation energy barrier for diffusion. Due to the lack of laboratory measurements on diffusion, prior astrochemical models usually assume that the diffusion pre-exponential factor is the same as that for desorption. This oversimplification may lead to an uncertainty in the model predictions. Recent laboratory measurements have found that the diffusion pre-exponential factor can differ from that for desorption by several orders of magnitude. However, the newly determined pre-exponential factor has not been tested in astrochemical models so far. Aims. We aim to evaluate the effect of the newly experimentally measured diffusion pre-exponential factor on the chemistry under cold molecular cloud conditions. Methods. We ran a set of parameters with different grain temperatures and diffusion barrier energies using the NAUTILUS astro-chemical code and compared the molecular abundance between the models with the abundance obtained using the experimentally determined pre-exponential factor for diffusion and with the abundance obtained using the values commonly adopted in prior models. Results. We found that statistically, more than half of the total gas-phase and grain surface species are not affected by the new pre-exponential factor after a chemical evolution of 105 yr. The most abundant gas-phase CO and grain surface water ice are not affected by the new pre-exponential factor. For the grain surface species that are affected, compared to the commonly adopted value of the pre-exponential factor for diffusion used in the chemical models, they could be either overproduced or underproduced with the lower diffusion pre-factor used in this work. The former case applies to radicals and the species that serve as reactants, while the latter case applies to complex organic molecules (COMs) on the grain and the species that rarely react with other species. Gas-phase species could also be affected due to the desorption of the grain surface species. The abundance of some gas-phase COMs could be varied by over one order of magnitude depending on the adopted grain surface temperature and/or the ratio of diffusion to desorption energy in the model. Key species whose diffusion pre-exponential factor significantly affects the model predictions were also evaluated, and these species include CH3OH, H2CO, and NO. Conclusions. The results presented in this study show that the pre-exponential factor is one of the basic and important parameters in astrochemical models. It strongly affects the chemistry and should be determined carefully. More experiments to determine the diffusion of grain surface species are helpful for constraining their properties. [ABSTRACT FROM AUTHOR]

Context. The chemical evolution of distant galaxies cannot be assessed from observations of individual stars, in contrast to the case of nearby galaxies. On the other hand, the study of the interstellar medium (ISM) offers an alternative way to reveal important properties of the chemical evolution of distant galaxies. The chemical enrichment of the ISM is produced by all the previous generations of stars and it is possible to precisely determine the metal abundances in the neutral ISM in galaxies. The chemical abundance patterns in the neutral ISM are determined by the gas metallicity, presence of dust (the depletion of metals into dust grains), and possible deviations due to specific nucleosynthesis, for example, α-element enhancements. Aims. We aim to derive the metallicities, dust depletion, and α-element enhancements in the neutral ISM of gas-rich mostly-metal-poor distant galaxies (Damped Lyman-α absorbers, DLAs). Furthermore, we aim to constrain the distribution of α-element enhancements with metallicity in these galaxies. Methods. We collected a literature sample of column density measurements of O, Mg, Si, S, Ti, Cr, Fe, Ni, Zn, P, and Mn in the neutral ISM of DLAs at redshifts of 0.60 < z < 3.40. We used this sample to define a golden sample of DLAs with constrained observations of Ti and at least one other α-element. By studying the abundance patterns, we determined the amount of dust depletion, solely based on the observed relative abundances of the α-elements. We then used the abundances of Fe-peak elements to determine the overall metallicity of each system, after correcting for dust depletion. In addition, we studied the deviations from the basic (linear) abundance patterns. We divided our sample into two groups of galaxies based on the widths of their absorption lines (Δv90 above or below 100 km s−1), which may be considered as a proxy for their dynamical mass. We characterised the distribution of the α-element enhancements as a function of metallicity for the galaxy population as a whole, by fitting a piecewise function (plateau, decline, plateau) to the data. Results. We observed systematic deviations from the basic abundance patterns for O, Mg, Si, S, Ti, and Mn, which we interpreted as α-element enhancements and a Mn underabundance. The distribution of the α-element enhancements with metallicity is different in the high-Δv90 and low-Δv90 groups of galaxies. We constrained the metallicity of the α-element knee for the high-Δv90 and low-Δv90 groups of galaxies to be −1.02±0.15 dex and −1.84±0.11 dex, respectively. The average α-element enhancement at the high-plateau is [α/Fe]=0.38±0.07 dex. On the other hand, Mn shows an underabundance in all DLAs in the golden sample of −0.36±0.07 dex, on average. Conclusions. We have constrained, for the first time, the distribution of the α-element enhancement with metallicity in the neutral ISM in distant galaxies. Less massive galaxies show an α-element knee at lower metallicities than more massive galaxies. This can be explained by a lower star formation rate in less massive galaxies. If this collective behaviour can be interpreted in the same way as it is for individual systems, this would suggest that more massive and metal-rich systems evolve to higher metallicities before the contribution of SN-Ia to [α/Fe] levels out that of core-collapse SNe. This finding may plausibly be supported by different SFRs in galaxies of different masses. Overall, our results offer important clues to the study of chemical evolution in distant galaxies. [ABSTRACT FROM AUTHOR]

Context. The first hydrostatic core (FHSC) phase is a brief stage in the protostellar evolution that is difficult to detect. Its chemical composition determine that of later evolutionary stages. Numerical simulations are the tool of choice to study these objects. Aims. Our goal is to characterize the chemical evolution of gas and dust during the formation of the FHSC. Moreover, we are interested in analyzing, for the first time with 3D magnetohydrodynamic (MHD) simulations, the role of grain growth in its chemistry. Methods. We postprocessed 2 × 105 tracer particles from a RAMSES non-ideal MHD simulation using the codes NAUTILUS and SHARK to follow the chemistry and grain growth throughout the simulation. Results. Gas-phase abundances of most of the C, O, N, and S reservoirs in the hot corino at the end of the simulation match the ice-phase abundances from the prestellar phase. Interstellar complex organic molecules such as methyl formate, acetaldehyde, and formamide are formed during the warm-up process. Grain size in the hot corino (nH > 1011 cm−3) increases forty-fold during the last 30 kyr, with negligible effects on its chemical composition. At moderate densities (1010 < nH < 1011 cm−3) and cool temperatures 15 < T < 50 K, increasing grain sizes delay molecular depletion. At low densities (nH ~ 107 cm−3), grains do not grow significantly. To assess the need to perform chemo-MHD calculations, we compared our results with a two-step model that reproduces well the abundances of C and O reservoirs, but not the N and S reservoirs. Conclusions. The chemical composition of the FHSC is heavily determined by that of the parent prestellar core. Chemo-MHD computations are needed for an accurate prediction of the abundances of the main N and S elemental reservoirs. The impact of grain growth in moderately dense areas delaying depletion permits the use of abundance ratios as grain growth proxies. [ABSTRACT FROM AUTHOR]

The assembly and build-up of neutral atomic hydrogen (H I) in galaxies is one of the most fundamental processes in galaxy formation and evolution. Studying this process directly in the early universe is hindered by the weakness of the hyperfine 21-cm H I line transition, impeding direct detections and measurements of the H I gas masses (MHI). Here we present a new method to infer MHI of high-redshift galaxies using neutral, atomic oxygen as a proxy. Specifically, we derive metallicity-dependent conversion factors relating the far-infrared [O I]-63 μm and [O I]-145 μm emission line luminosities and MHI in star-forming galaxies at z ≈ 2 − 6 using gamma-ray bursts (GRBs) as probes. We calibrate the [O I]-to-H I conversion factor relying on a sample of local galaxies with direct measurements of MHI and [O I]-63 μm and [O I]-145 μm line luminosities in addition to the SIGAME hydrodynamical simulation framework at similar epochs (z ≈ 0). We find that the [O I]63 μm-to-H I and [O I]145 μm-to-H I conversion factors, here denoted β[OI]−63 μm and β[OI]−145 μm, respectively, universally appear to be anti-correlated with the gas-phase metallicity. The GRB measurements further predict a mean ratio of L[OI]−63 μm/L[OI]−145 μm = 1.55 ± 0.12 and reveal generally less excited [C II] over [O I] compared to the local galaxy sample. The z ≈ 0 galaxy sample also shows systematically higher β[OI]−63 μm and β[OI]−145 μm conversion factors than the GRB sample, indicating either suppressed [O I] emission in local galaxies likely due to their lower hydrogen densities or more extended, diffuse H I gas reservoirs traced by the H I 21-cm. Finally, we apply these empirical calibrations to the few detections of [O I]-63 μm and [O I]-145 μm line transitions at z ≈ 2 from the literature and further discuss the applicability of these conversion factors to probe the H I gas content in the dense, star-forming interstellar medium (ISM) of galaxies well into the epoch of reionization. [ABSTRACT FROM AUTHOR]

The metal content of galaxies provides a window into their formation in the full context of the cosmic baryon cycle. In this study, we examine the relationship between stellar mass and stellar metallicity (MZ*R) in the hydrodynamic simulations Illustris, TNG, and EAGLE (Evolution and Assembly of GaLaxies and their Environment) to understand the global properties of stellar metallicities within the feedback paradigm employed by these simulations. Interestingly, we observe significant variations in the overall normalization and redshift evolution of the MZ*R across the three simulations. However, all simulations consistently demonstrate a tertiary dependence on the specific star formation rate (sSFR) of galaxies. This finding parallels the relationship seen in both simulations and observations between stellar mass, gas-phase metallicity, and some proxy of galaxy gas content (e.g. SFR, gas fraction, and atomic gas mass). Since we find this correlation exists in all three simulations, each employing a subgrid treatment of the dense, star-forming interstellar medium (ISM) to simulate smooth stellar feedback, we interpret this result as a fairly general feature of simulations of this kind. Furthermore, with a toy analytic model, we propose that the tertiary correlation in the stellar component is sensitive to the extent of the 'burstiness' of feedback within galaxies. [ABSTRACT FROM AUTHOR]

Chloronium, H2Cl+, is detected in astrophysical media. It is key chemical intermediate for understanding of the physical chemistry of chlorine species there. At present, we compute the collision rates for the rotational excitation and de-excitation of ortho- and para- H2Cl+ colliding with He for T  ≤ 150 K, relevant for the interstellar medium (ISM) conditions. Prior to that, we generated the 3D interaction potential of the weakly bound H2Cl+-He complex along the Jacobi coordinates. For electronic structure computations, we used a post-Hartree-Fock explicitly correlated method at the CCSD(T)-F12/aug-cc-pVTZ level. The analytical expansion of this potential was incorporated into close coupling computations of the cross-sections for the rotational excitation and de-excitation of ortho- and para- H2Cl+ colliding with He and for collision kinetic energies E k ≤ 1000 cm−1. The rates were obtained after averaging these cross-sections over a Maxwell–Boltzmann distribution of kinetic energies. Our data show that the ∆j=∆ka=∆kc=−1 de-excitation transitions exhibit the largest values, in particular those used to identify this cation in the surveys. Besides, our results should help for determining more accurate abundances of H2Cl+ in the ISM and thus better modelling the chlorine chemistry there. [ABSTRACT FROM AUTHOR]

The presence of carbon-chain molecules in the interstellar medium (ISM) has been known since the early 1970s and > 130 such species have been identified to date, making up ∼ 43 % of the total of detected ISM molecules. They are prevalent not only in star-forming regions in our Galaxy but also in other galaxies. These molecules provide important information on physical conditions, gas dynamics, and evolutionary stages of star-forming regions. Larger species of polycyclic aromatic hydrocarbons (PAHs) and fullerenes (C60 and C70), which may be related to the formation of the carbon-chain molecules, have been detected in circumstellar envelopes around carbon-rich Asymptotic Giant Branch (AGB) stars and planetary nebulae, while PAHs are also known to be a widespread component of the ISM in most galaxies. Recently, two line survey projects toward Taurus Molecular Cloud-1 with large single-dish telescopes have detected many new carbon-chain species, including molecules containing benzene rings. These new findings raise fresh questions about carbon-bearing species in the Universe. This article reviews various aspects of carbon-chain molecules, including observational studies, chemical simulations, quantum calculations, and laboratory experiments, and discusses open questions and how future facilities may answer them. [ABSTRACT FROM AUTHOR]

Geostatistical methods are powerful tools for understanding the spatial structure of the metallicity distribution of galaxies, and enable construction of accurate predictive models of the 2D metallicity distribution. However, so far these methods have only been applied to very high spatial resolution metallicity maps, leaving it uncertain if they will work on lower quality data. In this study, we apply geostatistical techniques to high-resolution spectroscopic maps of three local galaxies convolved to eight different spatial resolutions ranging from ∼40 pc to ∼1 kpc per pixel. We fit a geostatistical model to the data at all resolutions, and find that for metallicity maps where small-scale structure is visible by eye (with ≳10 resolution elements per R e), all parameters, including the metallicity correlation scale, can be recovered accurately. At all resolutions tested, we find that point metallicity predictions from such a geostatistical model outperform a circularly symmetric metallicity gradient model. We also explore dependence on the number of data points, and find that N ≳ 100 spatially resolved metallicity values are sufficient to train a geostatistical model that yields more accurate metallicity predictions than a radial gradient model. Finally, we investigate the potential detrimental effects of having spaxels smaller than an individual H  ii region by repeating our analysis with metallicities integrated over H  ii regions. We see that spaxel-based measurements have more noise, as expected, but the underlying spatial metallicity distribution can be recovered regardless of whether spaxels or integrated regions are used. [ABSTRACT FROM AUTHOR]

Spectrophotometric data of the young planetary nebula M 3-27, from 2004 to 2021, are presented and discussed. We corroborate that the H  i Balmer lines present features indicating they are emitted by the central star, therefore He  i lines were used to correct line fluxes by effects of reddening. Important variability on the nebular emission lines between 1964 and 2021, probably related to density changes in the nebula, is reported. Diagnostic diagrams to derive electron temperatures and densities have been constructed. The nebula shows a very large density contrast with an inner density of the order of 107 cm−3 and an outer density of about 103–104 cm−3. With these values of density, electron temperatures of 16 000–18 000 K have been found from collisionally excited lines. Because the central star emits in the H+ lines, ionic abundances relative to He+ were calculated from collisionally excited and recombination lines, and scaled to H+ by considering that He+/H+ = He/H = 0.11. Abundance discrepancy factor (O+2) values were also determined. Total abundance values obtained indicate sub-solar abundances, similar to what is found in other comparable objects like IC 4997. [ABSTRACT FROM AUTHOR]

We present the results of a sensitive search for high-velocity gas in interstellar absorption lines associated with the Cygnus Loop supernova remnant (SNR). We examine high-resolution high signal-to-noise ratio optical spectra of six stars in the Cygnus Loop region with distances greater than ∼700 pc. All stars show low-velocity Na  i and Ca  ii absorption. However, only one star, HD 198301, exhibits high-velocity Ca  ii absorption components, at velocities of +62, +82, and  +96 km s−1. The distance to this star of ∼870 pc helps to constrain the distance to the receding edge of the Cygnus Loop's expanding shock front. One of our targets, HD 335334, was previously thought to exhibit high positive and high negative velocity interstellar Na  i and Ca  ii absorption. This was one factor leading Fesen et al. to derive a distance to the Cygnus Loop of 725 ± 15 pc. However, we find that HD 335334 is in fact a double-line spectroscopic binary and shows no evidence of high-velocity interstellar absorption. As such, the distance to HD 335334 cannot be used to constrain the distance to the Cygnus Loop. Our detection of Ca  ii absorption approaching 100 km s−1 toward HD 198301 is the first conclusive detection of high-velocity absorption from a low-ionization species associated with the Cygnus Loop SNR. A large jump in the Na  i column density toward BD+31 4218, a star located beyond the northwestern boundary of the Cygnus Loop, helps to constrain the distance to a large molecular cloud complex with which the Cygnus Loop is evidently interacting. [ABSTRACT FROM AUTHOR]

This document is a correction to a previous article titled "Comparing emission- and absorption-based gas-phase metallicities in GRB host galaxies at z = 2−4 using JWST." The correction addresses two errors in the original paper. Firstly, the redshift of the host galaxy of GRB 090323 was mistakenly reported as z = 4.7, when it is actually at redshift z = 3.58. Secondly, there was a bug in the code that produced the surface brightness maps of the host galaxies of GRB 050820A and GRB 150403A, causing the labelled physical pixel scale to be too small. These errors have been corrected, and the updated maps are provided in the correction. [Extracted from the article]