Search

Despite their chemical simplicity, the spectroscopic investigation of light hydrides, such as hydrogen sulfide, is challenging due to strong hyperfine interactions and/or anomalous centrifugal-distortion effects. Several hydrides have already been detected in the interstellar medium, and the list includes H2S and some of its isotopologues. Astronomical observation of isotopic species and, in particular, those bearing deuterium is important to gain insights into the evolutionary stage of astronomical objects and to shed light on interstellar chemistry. These observations require a very accurate knowledge of the rotational spectrum, which is so far limited for mono-deuterated hydrogen sulfide, HDS. To fill this gap, high-level quantum-chemical calculations and sub-Doppler measurements have been combined for the investigation of the hyperfine structure of the rotational spectrum in the millimeter- and submillimeter-wave region. In addition to the determination of accurate hyperfine parameters, these new measurements together with the available literature data allowed us to extend the centrifugal analysis using a Watson-type Hamiltonian and a Hamiltonian-independent approach based on the Measured Active Ro-Vibrational Energy Levels (MARVEL) procedure. The present study thus permits to model the rotational spectrum of HDS from the microwave to far-infrared region with great accuracy, thereby accounting for the effect of the electric and magnetic interactions due to the deuterium and hydrogen nuclei. [ABSTRACT FROM AUTHOR]

A recent work [Ye et al. Mon. Not. R. Astron. Soc.2023, 525, 1158] on the gas‐phase formation of t‐HC(O)SH, already detected in the interstellar medium, pointed out that the trans form of HC(S)OH is a potential candidate for astronomical observations. Prompted by these results, the CH2SO family of isomers has been investigated from an energetic point of view using a double‐hybrid density functional in combination with a partially augmented triple‐zeta basis set. This preliminary study showed that the most stable species of the family are the cis and trans forms of HC(O)SH and HC(S)OH. For their structural and spectroscopic characterization, a composite scheme based on coupled cluster (CC) calculations that incorporates up to the quadruple excitations and accounts for the extrapolation to the complete basis set limit and core correlation effects has been employed. This approach opens to the prediction of rotational constants with an accuracy of 0.1%. A hybrid scheme, based on harmonic frequencies computed using the CC singles, doubles and a perturbative treatment of triples method (CCSD(T)) in conjunction with a quadruple‐zeta basis set, allowed us to obtain fundamental vibrational frequencies with a mean absolute error of about 1%. [ABSTRACT FROM AUTHOR]

Accurate modeling of astrophysical jets is critical for understanding accretion systems and their impact on the interstellar medium. While astronomical observations can validate models, they have limitations. Controlled laboratory experiments offer a complementary approach for qualitative and quantitative demonstration. Laser experiments offer a complementary approach. This article introduces a new platform on the OMEGA laser facility for high-velocity (1500 kms−1), high-aspect-ratio (∼36) jet creation with strong cylindrical symmetry. This platform's capabilities bridge observational gaps, enabling controlled initial conditions and direct measurements of plasma characteristics, crucial for refining astrophysical jet dynamics and improving the models accuracy. [ABSTRACT FROM AUTHOR]

The article is a book review of "Cosmochemistry, 2nd edition" by Harry McSween Jr. and Gary Huss. The book is a revised and updated version of a textbook originally published in 2010. It covers the study of the chemical compositions of the universe and its constituents, drawing on various scientific disciplines. The new edition includes improvements such as clearer figures, updated content reflecting recent discoveries, and additional color plates. Each chapter is well-organized and includes introductory paragraphs, summaries, comprehension questions, suggestions for further reading, and bibliographies. The book is suitable for upper-level undergraduate or graduate courses. [Extracted from the article]

The purine nucleobases adenine and guanine are complex organic molecules that are essential for life. Despite their ubiquitous presence on Earth, purines have yet to be detected in observations of astronomical environments. This work therefore proposes to study the infrared spectra of purines linked to terrestrial biochemical processes under conditions analogous to those found in the interstellar medium. The infrared spectra of adenine and guanine, both in neat form and embedded within an ice made of H2O:NH3:CH4:CO:CH3OH (10:1:1:1:1), were analysed with the aim of determining which bands attributable to adenine and/or guanine can be observed in the infrared spectrum of an astrophysical ice analogue rich in other volatile species known to be abundant in dense molecular clouds. The spectrum of adenine and guanine mixed together was also analysed. This study has identified three purine nucleobase infrared absorption bands that do not overlap with bands attributable to the volatiles that are ubiquitous in the dense interstellar medium. Therefore, these three bands, which are located at 1255, 940, and 878 cm−1, are proposed as an infrared spectral signature for adenine, guanine, or a mixture of these molecules in astrophysical ices. All three bands have integrated molar absorptivity values (ψ) greater than 4 km mol−1, meaning that they should be readily observable in astronomical targets. Therefore, if these three bands were to be observed together in the same target, then it is possible to propose the presence of a purine molecule (i.e., adenine or guanine) there. [ABSTRACT FROM AUTHOR]

Sulphur is an important and ubiquitous element of the interstellar medium (ISM). Despite its importance, its chemistry still needs to be elucidated, with one of the main issues being the missing sulphur problem. In this work, small molecular species, already detected in the ISM (SH, OH, H2CS, H2CO, H2S, H2O, HCS/HSC, and HCO), were combined to set five different gas-phase reactions for the formation of isomers belonging to the CH2SO family, with one of its member, namely trans -HC(O)SH, already identified as well. Through a state-of-the-art computational study, it has been found that, thermochemically, only one of the reactions considered is open in the ISM conditions: H2CS + OH can produce cis / trans -HC(S)OH and cis / trans -HC(O)SH via hydrogen-atom loss. Kinetically, the favoured product is trans -HC(S)OH followed by trans -HC(O)SH. In view of the recent detection of this latter, our study suggests that trans -HC(S)OH is a good candidate for astronomical observations. Since this species has never been studied experimentally, as a first step towards its laboratory characterization, accurate estimates of the rotational constants have been provided. [ABSTRACT FROM AUTHOR]

As of yet, unexamined aluminum bearing molecules may help elucidate aluminum chemistry and associated refractory atom reactions in the interstellar medium. The flexibility of modern quantum chemistry in the construction and analysis of novel molecules makes it perfectly suited to analyze molecules of astrochemical significance. In this paper, high level ab initio electronic structure calculations using the coupled cluster CCSD(T) and explicitly correlated coupled cluster CCSD(T)-F12 methods with large basis sets extrapolated to the complete basis set limit have been performed on the various [Al,N,C,O] isomers. The anharmonic rotational and vibrational spectroscopic parameters for all isomers are produced with these same levels of theory via quartic force fields and vibrational perturbation theory in order to aid in their potential laboratory or even astrophysical identification. The most stable isomer is determined here to be the aluminum isocyanate radical with linear equilibrium geometry AlNCO (X1Σ+). The NCO antisymmetric stretch of AlNCO has an intensity of 1500 km/mol, which should greatly aid in its infrared detection in the region around 2305 cm−1. Additionally, the AlOCN isomer is relatively low lying, possesses a 5.12 D dipole moment, and has a notable kinetic stability, making it a viable candidate for astronomical observation. All isomers are characterized by small frequencies, which indicates that these are floppy molecules. Isomers with a terminal aluminum atom are especially floppy, with bending modes less than 100 cm−1. [ABSTRACT FROM AUTHOR]

The chemistry of the interstellar medium occurs under extreme conditions and can lead to the formation of exotic molecules. These are species that on Earth are unstable and/or highly reactive. Their discovery in space is usually based on the astronomical observation of their rotational fingerprints, which requires an accurate laboratory investigation. This is based on a strategy that starts from the interplay of experiment and theory. State-of-the-art quantum-chemical calculations are used to predict the relevant spectroscopic information required to guide the spectral recording, analysis and assignment. Rotational spectra measurements are then performed in the centimeter-/millimeter-/submillimeter-wave region, thereby exploiting efficient on-the-fly production protocols for exotic molecules. Subsequently, the spectral analysis leads to accurate spectroscopic parameters, which are then used for setting up accurate line catalogs for astronomical searches and detections. This review is based on the strategy developed and the results obtained at the ROT&Comp Lab of the University of Bologna.

In this paper, the results of a comprehensive theoretical investigation of neutral HCnH0 and charged HCnH± chains are reported using state‐of‐the‐art compound model chemistries (W1BD, G4, CBS‐QB3, CBS‐APNO, CBS‐4M) and single point methods (including "gold standard" CCSD(T)). The properties envisaged include electronic and chemical bonding structure data, enthalpies of formation, adiabatic and vertical ionization (IP), and electron attachment (EA) energies, gas phase acidities, C−H bond strengths, and chain "deprotecting" (HCnH → H + Cn + H) energies. The best theoretical estimates based on composite models reported here for the various properties investigated agree with the available experimental data and are better than all previous theoretical estimates. To exemplify, for the enthalpies of formation, the G4 composite model achieves a RSMD (root square mean deviation) of 0.28 kcal mol−1 and a MUD (maximum unsigned deviation) of 0.45 kcal mol−1. Most importantly from the astrochemical perspective, it is predicted that the stable HCnH− anions with n≤8$n\le 8$ are nonlinear. Having sufficiently large dipole moments, the anion HCnH−cis conformers are potential candidates for detection in space via rovibrational spectroscopy. [ABSTRACT FROM AUTHOR]

The processes and reactions that led to the formation of the first biomolecules on Earth play a key role in the highly debated theme of the origin of life. Whether the first chemical building blocks were generated on Earth (endogenous synthesis) or brought from space (exogenous delivery) is still unanswered. The detection of complex organic molecules in the interstellar medium provides valuable support to the latter hypothesis. To gather more insight, here we provide the astronomers with accurate rotational frequencies to guide the interstellar search of 3-aminoisoxazole, which has been recently envisaged as a key reactive species in the scenario of the so-called RNA-world hypothesis. Relying on an accurate computational characterization, we were able to register and analyze the rotational spectrum of 3-aminoisoxazole in the 6–24 GHz and 80–320 GHz frequency ranges for the first time, exploiting a Fourier-transform microwave spectrometer and a frequency-modulated millimeter/sub-millimeter spectrometer, respectively. Due to the inversion motion of the −NH2 group, two states arise, and both of them were characterized, with more than 1300 lines being assigned. Although the fit statistics were affected by an evident Coriolis interaction, we were able to produce accurate line catalogs for astronomical observations of 3-aminoisoxazole. [ABSTRACT FROM AUTHOR]

For decades, sulfur has remained underdetected in molecular form within the dense interstellar medium (ISM), and somewhere a molecular sulfur sink exists where it may be hiding. With the discovery of hydrogen peroxide (HOOH) in the ISM in 2011, a natural starting point may be found in sulfur-bearing analogs that are chemically similar to HOOH: hydrogen thioperoxide (HOSH) and hydrogen persulfide (HSSH). The present theoretical study couples the accuracy in the anharmonic fundamental vibrational frequencies from the explicitly correlated coupled cluster theory with the accurate rotational constants provided by canonical high-level coupled cluster theory to produce rovibrational spectra for use in the potential observation of HOSH and HSSH. The ν 6 mode for HSSH at 886.1 cm − 1 is within 0.2 cm − 1 of the gas-phase experiment, and the B 0 rotational constant for HSSH of 6979.5 MHz is within 9.0 MHz of the experimental benchmarks, implying that the unknown spectral features (such as the first overtones and combination bands) provided herein are similarly accurate. Notably, a previous experimentally-attributed 2 ν 1 mode, at 7041.8 cm − 1 , has been reassigned to the ν 1 + ν 5 combination band based on the present work's ν 1 + ν 5 value at 7034.3 cm − 1 . The most intense vibrational transitions for each molecule are the torsions, with HOSH having a more intense transition of 72 km/mol compared to HSSH's intensity of 14 km/mol. Furthermore, HOSH has a larger net dipole moment of 1.60 D compared to HSSH's 1.15 D. While HOSH may be the more likely candidate of the two for possible astronomical observation via vibrational spectroscopy due to the notable difference in their intensities, both HSSH and HOSH have large enough net dipole moments to be detectable by rotational spectroscopy to discover the role these molecules may have as possible molecular sulfur sinks in the dense ISM. [ABSTRACT FROM AUTHOR]

To be detectable in space via radio astronomy, molecules should have a permanent dipole moment. This is the plausible reason why HCnH chains are underproportionally represented in the interstellar medium in comparison with the isoelectronically equivalent HCnN chain family, which is the most numerous homologous series astronomically observed so far. In this communication, we present results of quantum chemical calculations for the HCnH family at several levels of theory: density functional theory (DFT/B3LYP), coupled-cluster expansions (ROCCSD(T)), and G4 composite model. Contradicting previous studies, we report here that linear HCnH− anion chains with sizes of astrochemical interest are unstable (i.e., not all calculated frequencies are real). Nonlinear cis and trans HCnH− anion chains turn out to be stable both against molecular vibrations (i.e., all vibrational frequencies are real) and against electron detachment (i.e., positive electroaffinity). The fact that the cis anion conformers possess permanent dipole is the main encouraging message that this study is aiming at conveying to the astrochemical community, as this makes them observable by means of radio astronomy. [ABSTRACT FROM AUTHOR]

Rate coefficients for transitions between the lower rotational levels of two isotopologs of hydrogen sulphide, specifically HDS and D2S, induced by collisions with para -H2 and ortho -H2 are presented in this work. The availability of these rate coefficients will allow accurate estimates to be made of the abundance of these species in the interstellar medium to be made from astronomical observations. The rate coefficients were computed in close-coupling calculations using potential energy surfaces (PESs) obtained by transformation of the H2S–H2 PES previously calculated with the explicitly correlated CCSD(T)-F12a coupled-cluster method. Rate coefficients for transitions between rotational levels with energies less than 196 cm−1 and temperatures from 5 to 400 K have been calculated for HDS, ortho -D2S, and para -D2S. The rate coefficients for the H2S–H2, HDS–H2, and D2S–H2 systems are compared [ABSTRACT FROM AUTHOR]

We present a synthesis of the astronomical observations constraining the wavelength-dependent extinction, emission, and polarization from interstellar dust from UV to microwave wavelengths on diffuse Galactic sight lines. Representative solid-phase abundances for those sight lines are also derived. Given the sensitive new observations of polarized dust emission provided by the Planck satellite, we place particular emphasis on dust polarimetry, including continuum polarized extinction, polarization in the carbonaceous and silicate spectroscopic features, the wavelength-dependent polarization fraction of the dust emission, and the connection between optical polarized extinction and far-infrared polarized emission. Together, these constitute a set of constraints that should be reproduced by models of dust in the diffuse interstellar medium. [ABSTRACT FROM AUTHOR]

Among all the interstellar complex organic molecules, acetaldehyde is one of the most widely detected species. The question of its formation route(s) is, therefore, of a major interest regarding astrochemical models. In this paper, we provide an extensive review of the gas-phase formation paths that were, or are, reported in the literature and the major astrochemical data bases. Four different gas-phase formation routes stand out : (1) CH3OCH3  + H+/CH3CHOH+  + e−, (2) C2H5  + O(3P), (3) CH3OH  + CH, and (4) CH3CH2OH  + OH/CH3CHOH  + O(3P). Paths (2) and (3) were not studied neither via laboratory nor theoretical works in the low temperature and density regime valid for the interstellar medium (ISM). Thus, we carried out new accurate quantum chemistry computations. A theoretical kinetics study at low temperatures (7 ÷ 300 K), adopting the Rice–Ramsperger–Kassel–Marcus scheme, was also performed. We confirm that reaction (2) is efficient in forming acetaldehyde in the 7–300 temperature range (α  = 1.21 × 10−10 cm3 s−1 and β = 0.16). On the contrary, our new computations disprove the formation of acetaldehyde through reaction (3) (α = 1.84 ÷ 0.67 × 10−13 cm3 s−1 and β = −0.07 ÷ −0.95). Path (1) was showed to be inefficient too by recent computations, while path (4) was formerly considered for glycolaldehyde formation, having acetaldehyde as a byproduct. In conclusions, of the four above paths, only two, the (2) and (4), are potentially efficient gas-phase reaction routes for the formation of acetaldehyde and we encourage astrochemical modellers to consider only them. Comparison with astronomical observations suggests that path (4) may actually play the major role. [ABSTRACT FROM AUTHOR]

Trend filtering – first introduced into the astronomical literature in Paper I of this series – is a state-of-the-art statistical tool for denoising 1D signals that possess varying degrees of smoothness. In this work, we demonstrate the broad utility of trend filtering to observational astronomy by discussing how it can contribute to a variety of spectroscopic and time-domain studies. The observations we discuss are (1) the Lyman-α (Lyα) forest of quasar spectra; (2) more general spectroscopy of quasars, galaxies, and stars; (3) stellar light curves with planetary transits; (4) eclipsing binary light curves; and (5) supernova light curves. We study the Lyα forest in the greatest detail – using trend filtering to map the large-scale structure of the intergalactic medium along quasar-observer lines of sight. The remaining studies share broad themes of: (1) estimating observable parameters of light curves and spectra; and (2) constructing observational spectral/light-curve templates. We also briefly discuss the utility of trend filtering as a tool for 1D data reduction and compression. [ABSTRACT FROM AUTHOR]

Dust particles play a major role in the formation, evolution and chemistry of interstellar clouds, stars, and planetary systems. Commonly identified forms include amorphous and crystalline carbon-rich particles and silicates. Also present in many astrophysical environments are polycyclic aromatic hydrocarbons (PAHs), detected through their infrared emission, and which are essentially small flakes of graphene. Astronomical observations over the past four decades have revealed a widespread unassigned 'extended red emission' (ERE) feature which is attributed to luminescence of dust grains. Numerous potential carriers for ERE have been proposed but none has gained general acceptance. In this Letter it is shown that there is a strong similarity between laboratory optical emission spectra of graphene oxide (GO) and ERE, leading to this proposal that emission from GO nanoparticles is the origin of ERE and that these are a significant component of interstellar dust. The proposal is supported by infrared emission features detected by the Infrared Space Observatory (ISO) and the Spitzer Space Telescope. [ABSTRACT FROM AUTHOR]

The article explores the presence of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium, revealing through isotopic analysis of Ryugu asteroid samples that some PAHs formed in cold interstellar clouds before the Solar System's formation.

• The low-lying electronic states of PN+ are calculated with the icMRCI + Q/56 + CV + DK method. • Transition probabilities of dipole allowed transitions of PN+ are presented. • Radiative lifetimes of some excited states are evaluated. • Spin-orbit coupling integrals between low-lying electronic states are computed. • The predissociation of 14Σ − (υ ' = 1)→16Σ+, 14Σ − (υ ' = 15)→16Π and 14Δ (υ ' = 19)→16Π are discussed. The PN+ cation is regarded as a candidate of ions which may exist in the interstellar medium. Accurate transition properties are desired to identify the spectra from astronomical observation. However, transition data of PN+ are relatively limited. In this work, the state-of-the-art ab initio calculations are carried out to investigate the low-lying electronic states of PN+ correlating to two lowest dissociation limits, its transition properties and its spin-orbit couplings. For the X2Σ+ and A2Π states, the calculated spectroscopic constants agree well with previous experimental data. For the other electronic states, the accuracy of the spectroscopic parameters is also ensured by comparing with previous theoretical results. Then, transition probabilities of dipole allowed transition systems are calculated. The radiative lifetimes of vibrational levels for the A2Π, 14Π, 14Δ, 14Σ−, and 24Π states are also evaluated. Such transition data can be used in the identification of PN+ in the laboratory or the interstellar space. Finally, the predissociation of 14Σ− (υ ' = 1)→16Σ+, 14Σ− (υ ' = 15)→16Π and 14Δ (υ '= 19)→16Π are analyzed with the help of spin-orbit coupling integrals. [ABSTRACT FROM AUTHOR]

Methyl mercaptan (CH3SH) is an important sulfur-bearing species in the interstellar medium, terrestrial environment, and potentially in planetary atmospheres. The aim of the present study is to provide accurate spectroscopic parameters for the most abundant minor isotopolog CH334SH to support radio astronomical observations at millimeter and submillimeter wavelengths. The rotational spectrum of CH334SH, which is complicated by the large-amplitude internal rotation of the CH3 group versus the 34SH frame, was investigated in the 49−510 GHz and 1.1−1.5 THz frequency ranges in natural isotopic abundance. The analysis of the spectrum was performed up to the second excited torsional state, and the obtained data were modeled with the RAM36 program. A fit within experimental accuracy was obtained with a RAM Hamiltonian model that uses 72 parameters. Predictions based on this fit are used to search for CH334SH with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the hot molecular core Sgr B2(N2), but blends with emission lines of other species prevent its firm identification in this source. [ABSTRACT FROM AUTHOR]

We present the first census of the interstellar Complex Organic Molecules (iCOMs) in the low-mass Class I protostar SVS13-A, obtained by analysing data from the IRAM-30 m Large Project ASAI (Astrochemical Surveys At IRAM). They consist of a high-sensitivity unbiased spectral survey at the 1mm, 2mm, and 3mm IRAM bands. We detected five iCOMs: acetaldehyde (CH3CHO), methyl formate (HCOOCH3), dimethyl ether (CH3OCH3), ethanol (CH3CH2OH), and formamide (NH2CHO). In addition, we searched for other iCOMs and ketene (H2CCO), formic acid (HCOOH) and methoxy (CH3O), whose only ketene was detected. The numerous detected lines, from 5 to 37 depending on the species, cover a large upper level energy range, between 15 and 254 K. This allowed us to carry out a rotational diagram analysis and derive rotational temperatures between 35 and 110 K, and column densities between 3 × 1015 and 1 × 1017 cm−2 on the 0.3 arcsec size previously determined by interferometric observations of glycolaldehyde. These new observations clearly demonstrate the presence of a rich chemistry in the hot corino towards SVS13-A. The measured iCOMs abundances were compared to other Class 0 and I hot corinos, as well as comets, previously published in the literature. We find evidence that (i) SVS13-A is as chemically rich as younger Class 0 protostars, and (ii) the iCOMs relative abundances do not substantially evolve during the protostellar phase. [ABSTRACT FROM AUTHOR]

The advent of new sub-millimetre (sub-mm) observational facilities has stimulated the desire to model the sub-mm line emission of galaxies within cosmological galaxy formation models. This is typically done by applying sub-resolution recipes to describe the properties of the unresolved interstellar medium (ISM). While there is freedom in how one implements sub-resolution recipes, the impact of various choices has yet to be systematically explored. We combine a semi-analytic model of galaxy formation with chemical equilibrium networks and numerical radiative transfer models and explore how different choices for the sub-resolution modelling affect the predicted CO, [C  i ], and [C  ii ] emission of galaxies. A key component for a successful model includes a molecular cloud mass–size relation and scaling for the ultraviolet and cosmic ray radiation field that depend on local ISM properties. Our most successful model adopts a Plummer radial density profile for gas within molecular clouds. Different assumptions for the clumping of gas within molecular clouds and changes in the molecular cloud mass distribution function hardly affect the CO, [C  i ], and [C  ii ] luminosities of galaxies. At fixed star formation rate, the [C  ii ]–SFR ratio of galaxies scales inversely with the pressure acting on molecular clouds, increasing the molecular clouds density and hence decreasing the importance of [C  ii ] line cooling. We find that it is essential that a wide range of sub-mm emission lines arising in vastly different phases of the ISM are used as model constraints in order to limit the freedom in sub-grid choices. [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter/submillimeter Array (ALMA) resolved observations of molecular gas in galaxies up to |$z$| = 0.35 to characterize the role of global galactic dynamics on the global interstellar medium properties. These observations consist of a sub-sample of 39 galaxies taken from the Valparaíso ALMA Line Emission Survey (VALES). From the CO(J = 1–0) emission line, we quantify the kinematic parameters by modelling the velocity fields. We find that the infrared (IR) luminosity increases with the rotational to dispersion velocity ratio (V rot/σ |$v$| , corrected for inclination). We find a dependence between V rot/σ |$v$| and the [C ii ]/IR ratio, suggesting that the so-called [C ii ] deficit is related to the dynamical state of the galaxies. We find that global pressure support is needed to reconcile the dynamical mass estimates with the stellar masses in our systems with low V rot/σ |$v$| values. The star formation rate (SFR) is weakly correlated with the molecular gas fraction (⁠|$f_{\rm H_2}$|⁠) in our sample, suggesting that the release of gravitational energy from cold gas may not be the main energy source of the turbulent motions seen in the VALES galaxies. By defining a proxy of the 'star formation efficiency' (SFE) parameter as the SFR divided by the CO luminosity (SFE′ ≡ SFR/ L |$^{\prime }_{\rm CO}$|⁠), we find a constant SFE′ per crossing time (t cross). We suggest that t crossmay be the controlling time-scale in which the star formation occurs in dusty |$z$| ∼ 0.03–0.35 galaxies. [ABSTRACT FROM AUTHOR]

Recent studies of the diffuse parts of molecular clouds have revealed the presence of parallel, ordered low-density filaments termed striations. Flows along magnetic field lines, Kelvin–Helmholtz instabilities and hydromagnetic waves are amongst the various formation mechanisms proposed. Through a synergy of observational, numerical, and theoretical analysis, previous studies singled out the hydromagnetic waves model as the only one that can account for the observed properties of striations. Based on the predictions of that model, we develop here a method for measuring the temporal evolution of striations through a combination of molecular and dust continuum observations. Our method allows us to not only probe temporal variations in molecular clouds but also estimate the strength of both the ordered and fluctuating components of the magnetic field projected on the plane of the sky. We benchmark our new method against chemical and radiative transfer effects through 2D magnetohydrodynamic simulations coupled with non-equilibrium chemical modelling and non-local thermodynamic equilibrium line radiative transfer. We find good agreement between theoretical predictions, simulations, and observations of striations in the Taurus molecular cloud. We find a value of |$\rm {27 \pm 7} ~\rm {\mu G}$| for the plane-of-sky magnetic field, in agreement with previous estimates via the Davis–Chandrasekhar–Fermi method, and a ratio of fluctuating to ordered component of the magnetic field of ∼10 per cent. [ABSTRACT FROM AUTHOR]

In this work, we have reported the results of multiwavelength study of the Fermi hard spectrum blazar B2 0806+35 using data from Swift, Fermi, and TACTIC observations. We analysed Swift /UVOT, Swift /XRT, Fermi /LAT, and TACTIC data to construct the sepctral energy distribution for different epochs over last 7 yr. We modelled the spectral energy distributions using one zone leptonic blazar emission model and emission from optically thick geometrically thin accretion disc around the black hole. It is shown that the photon spectrum in the GeV–TeV energy range is steep and the source is not a good candidate to study intergalactic magnetic field. It is also shown that the accretion disc is systematically receding from the central black hole and the accretion flow is possibly advection dominated. [ABSTRACT FROM AUTHOR]

We present the results of our photometric UBV JHKL observations for the symbiotic star V1413 Aql obtained in 2012-2018. An analysis of the data has shown that inMay 2017 the system passed to a quiescent state with B − V ≈ 0ṃ 6 for the first time since 1993. It lasted no more than five months. The J − K color at the primary minimum of 2012 reached 1ṃ 5, which, given the interstellar reddening, corresponds to spectral type M5-M6 III of the cool component. A secondary minimum has been detected at φ ≈ 0.5 on the JK phase light curves constructed for the dates of observations with B ≥ 13. [ABSTRACT FROM AUTHOR]

The quest for other habitable worlds and the search for life among them are major goals of modern astronomy. One way to make progress towards these goals is to obtain high-quality spectra of a large number of exoplanets over a broad range of wavelengths. While concepts currently investigated in the United States are focused on visible/NIR wavelengths, where the planets are probed in reflected light, a compelling alternative to characterize planetary atmospheres is the mid-infrared waveband (5-20 μm). Indeed, mid-infrared observations provide key information on the presence of an atmosphere, the surface conditions (e.g., temperature, pressure, habitability), and the atmospheric composition in important species such as H2O, CO2, O3, CH4, and N2O. This information is essential to investigate the potential habitability of exoplanets and to make progress towards the search for life in the Universe. Obtaining high-quality mid-infrared spectra of exoplanets from the ground is however extremely challenging due to the overwhelming brightness and turbulence of the Earth's atmosphere. In this paper, we present a concept of space-based mid-infrared interferometer that can tackle this observing challenge and discuss the main technological developments required to launch such a sophisticated instrument. [ABSTRACT FROM AUTHOR]

We present extensive spectroscopic observations for one of the closest Type Ia supernovae (SNe Ia), SN 2014J discovered in M82, ranging from 10.4 d before to 473.2 d after B -band maximum light. The diffuse interstellar band features detected in a high-resolution spectrum allow an estimate of line-of-sight extinction as A v ∼ 1.9 ± 0.6 mag. Spectroscopically, SN 2014J can be put into the high-velocity (HV) subgroup in Wang's classification with a velocity of Si  ii λ 6355 at maximum light of |$v$| 0 = 1.22 ± 0.01 × 104 km s−1 but has a low velocity gradient (LVG, following Benetti's classification) of |$\dot{v}=41\pm 2$| km s−1 d−1, which is inconsistent with the trend that HV SNe Ia generally have larger velocity gradients. We find that the HV SNe Ia with LVGs tend to have relatively stronger Si  iii (at ∼4400 Å) absorptions in early spectra, larger ratios of S  ii λ 5468 to S  ii λ 5640, and weaker Si  ii 5972 absorptions compared to their counterparts with similar velocities but high velocity gradients. This shows that the HV+LVG subgroup of SNe Ia may have intrinsically higher photospheric temperature, which indicates that their progenitors may experience more complete burning in the explosions relative to the typical HV SNe Ia. [ABSTRACT FROM AUTHOR]

Recent observations of several protoplanetary discs have found evidence of departures from flat, circular motion in the inner regions of the disc. One possible explanation for these observations is a disc warp, which could be induced by a planet on a misaligned orbit. We present three-dimensional numerical simulations of the tidal interaction between a protoplanetary disc and a misaligned planet. For low planet masses, we show that our simulations accurately model the evolution of inclined planet orbit (up to moderate inclinations). For a planet massive enough to carve a gap, the disc is separated into two components and the gas interior and exterior to the planet orbit evolve separately, forming an inner and outer disc. Due to the inclination of the planet, a warp develops across the planet orbit such that there is a relative tilt and twist between these discs. We show that when other parameters are held constant, the relative inclination that develops between the inner and outer disc depends on the outer radius of the total disc modelled. For a given disc mass, our results suggest that the observational relevance of the warp depends more strongly on the mass of the planet rather than the inclination of the orbit. [ABSTRACT FROM AUTHOR]

Gaussian processes (GPs) are the ideal tool for modelling the Galactic interstellar medium, combining statistical flexibility with a good match to the underlying physics. In an earlier paper, we outlined how they can be employed to construct three-dimensional maps of dust extinction from stellar surveys. GPs scale poorly to large data sets though, which put the analysis of realistic catalogues out of reach. Here, we show how a novel combination of the expectation propagation method and certain sparse matrix approximations can be used to accelerate the dust mapping problem. We demonstrate, using simulated Gaia data, that the resultant algorithm is fast, accurate, and precise. Critically, it can be scaled up to map the Gaia catalogue. [ABSTRACT FROM AUTHOR]

Context. A large fraction of the interstellar medium can be characterized as a multiphase medium. The neutral hydrogen gas is bistable with cold and warm neutral medium (CNM and WNM respectively) but there is evidence for an additional phase at intermediate temperatures, a lukewarm neutral medium (LNM) that is thermally unstable. Aims. We use all sky data from the HI4PI survey to separate these neutral H I phases with the aim to determine their distribution and phase fractions f in the local interstellar medium. Methods. HI4PI observations, gridded on an nside = 1024 HEALPix grid, were decomposed into Gaussian components. From the frequency distribution of the velocity dispersions we infer three separate linewidth regimes. Accordingly we extract the H I line emission corresponding to the CNM, LNM, and WNM. We generateed all-sky maps of these phases in the local H I gas with − 8 < vLSR < 8 km s−1. Results. Each of the H I phases shows distinct structures on all scales. The LNM never exists as a single phase but contributes on average 41% of the H I. The CNM is prominent only for 22% of the sky, contributes there on average 34% but locally up to 60% of the H I and is associated with dust at temperatures Tdust ~ 18.6 K. Embedded cold filaments show a clear anti-correlation between CNM and LNM. Also the smoothly distributed WNM is anti-correlated with the CNM. It contributes for the rest of the sky 39% with dust associated at temperatures Tdust ~ 19.4 K. Conclusions. The CNM in filaments exists on small scales. Here the observed anti-correlation between LNM and CNM implies that both, filaments and the surrounding more extended LNM, must have a common origin. [ABSTRACT FROM AUTHOR]

We present a new radio-selected sample of PNe from the CORNISH survey. This is a radio continuum survey of the inner Galactic plane covering Galactic longitude, 10° < l < 65° and latitude, | b | < 1° with a resolution of 1.5 arcsec and sensitivity better than 0.4 mJy  beam−1. The radio regime, being unbiased by dust extinction, allows for a more complete sample selection, especially towards the Galactic mid-plane. Visual inspection of the CORNISH data, in combination with data from multiwavelength surveys of the Galactic plane, allowed the CORNISH team to identify 169 candidate PNe. Here, we explore the use of multiwavelength diagnostic plots and analysis to verify and classify the candidate PNe. We present the multiwavelength properties of this new PNe sample. We find 90 new PNe, of which 12 are newly discovered and 78 are newly classified as PNe. A further 47 previously suspected PNe are confirmed as such from the analysis presented here and 24 known PNe are detected. Eight sources are classified as possible PNe or other source types. Our sample includes a young sub-sample, with physical diameters <0.12 pc, brightness temperatures (>1000 K) and located closer than 7 kpc. Within this sample is a water-maser PN with a spectral index of −0.55 ± 0.08, which indicates non-thermal radio emission. Such a radio-selected sample, unaffected by extinction, will be particularly useful to compare with population synthesis models and should contribute to the understanding of the formation and evolution of PNe. [ABSTRACT FROM AUTHOR]

The Slug Nebula is one of the largest and most luminous Lyman-α (Ly α) nebulae discovered to date, extending over 450 kpc around the bright quasar UM287 at z = 2.283. Characterized by high surface brightnesses over intergalactic scales, its Ly α emission may either trace high-density ionized gas ('clumps') or large column densities of neutral material. To distinguish between these two possibilities, information from a non-resonant line such as H α is crucial. Therefore, we analysed a deep Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) observation of one of the brightest Ly α-emitting regions in the Slug Nebula with the goal of detecting associated H α emission. We also obtained a deep, moderate resolution Ly α spectrum of the nearby brightest region of the Slug. We detected an H α flux of F $$_{\rm {H\, \alpha }}= 2.62\pm 0.47 \times 10^{-17}$$ erg cm−2 s−1 (SB $$_{\rm {H\, \alpha }}=2.70\pm 0.48 \times 10^{-18}$$  erg cm−2 s−1 arcsec−2 at the expected spatial and spectral location. Combining the H α detection with its corresponding Ly α flux (determined from the narrow-band imaging), we calculate a flux ratio of $${F_{\rm Ly\alpha }}/{F_{\rm H\, \alpha }}=5.5\pm 1.1$$. The presence of a skyline at the location of the H α emission decreases the signal-to-noise ratio of the detection and our ability to put stringent constraints on the H α kinematics. Our measurements argue for the origin of the Ly α emission being recombination radiation, suggesting the presence of high-density ionized gas. Finally, our high-resolution spectroscopic study of the Ly α emission does not show evidence of a rotating disc pattern and suggest a more complex origin for at least some parts of the Slug Nebula. [ABSTRACT FROM AUTHOR]

We report the discovery of the most distant radio galaxy to date, TGSS J1530+1049 at a redshift of $$z$$ = 5.72, close to the presumed end of the Epoch of Reionization. The radio galaxy was selected from the TGSS ADR1 survey at 150 MHz for having an ultra-steep spectral index, $$\alpha ^{\text{{150 MHz}}}_{\text{{1.4 GHz}}} = -1.4$$ and a compact morphology obtained using VLA imaging at 1.4 GHz. No optical or infrared counterparts for the radio source were found in publicly available sky surveys. Follow-up optical spectroscopy at the radio position using GMOS on Gemini North revealed the presence of a single emission line. We identify this line as Lyman alpha at $$z$$ = 5.72, because of its asymmetric line profile, the absence of other optical/UV lines in the spectrum, and a high equivalent width. With an Lyα luminosity of 5.7 × 1042 erg s−1 and an FWHM of 370 km s−1, TGSS J1530+1049 is comparable to 'non-radio' Lyman alpha emitters (LAEs) at a similar redshift. However, with a radio luminosity of log  L 150MHz = 29.1 W Hz−1 and a deconvolved physical size 3.5 kpc, its radio properties are similar to other known radio galaxies at $$z$$ > 4. Subsequent J and K band imaging using LUCI on the Large Binocular Telescope resulted in non-detection of the host galaxy down to 3σ limits of J > 24.4 and K > 22.4 (Vega). The K band limit is consistent with $$z$$ > 5 from the K − $$z$$ relation for radio galaxies and helps rule out low redshifts. The stellar mass limit derived using simple stellar population models is M stars < 1010.5 M⊙. Its relatively low stellar mass and small radio and Lyα sizes suggest that TGSS J1530+1049 may be a radio galaxy in an early phase of its evolution. [ABSTRACT FROM AUTHOR]

We performed a detailed photometric analysis and photoionization modelling on three high-excitation multiple-shell planetary nebulae: NGC 3242, NGC 6826, and NGC 7662. Archival Hubble Space Telescope/ Wide Field Planetary Camera 2 (HST /WFPC2) narrow band filter images were used to investigate shocked regions by two independent methods: using low-excitation ions (via H α/[N  ii ] versus H α/[S  ii ] extended diagnostic diagrams) and by means of high-excitation species looking for regions of enhanced [O  iii ]/H α line ratios. Shocked region analysis via low-excitation ions shows that major deviations from the general inside to outside ionization trend correspond only to regions where fast low-ionization emission regions or low-ionization emission line structures are located. The reduction on the signal-to-noise ratio at the outskirts of the [O  iii ]/H α ratio maps made us unable to unambiguously identified for an enhancement on the [O  iii ]/H α line ratio as an indicator for shocks. For non-shocked regions, we performed a photoionization modelling using cloudy. Fittings to the [O  iii ]- and H α-observed radial profiles lead us to constrain on the free parameters of the density laws and filling factors together to temperatures and luminosities for the CSPNe. Best-fitting models show a very well representation of the [O  iii ] and H α emission. Discrepancies in the model fittings to the [N  ii ] and [S  ii ] profiles at NGC 6826 and NGC 3242 can be attributed in the former case, due to a contamination by the light of the CSPN and, in the latter case, either due to gas inhomogeneities within the clumps or to a leaking of ultraviolet radiation. [ABSTRACT FROM AUTHOR]

We present the Technicolor Dawn simulations, a suite of cosmological radiation hydrodynamic simulations of the first 1.2 billion yr. By modelling a spatially inhomogeneous ultraviolet background (UVB) on the fly with 24 frequencies and resolving dark matter haloes down to 108 M⊙ within 12  h −1 Mpc volumes, our simulations unify observations of the intergalactic and circumgalactic media, galaxies, and reionization into a common framework. The only empirically tuned parameter, the fraction f esc,gal($$z$$) of ionizing photons that escape the interstellar medium, is adjusted to match observations of the Lyman-α forest and the cosmic microwave background. With this single calibration, our simulations reproduce the history of reionization; the stellar mass and star formation rate relation of galaxies; the number density and metallicity of damped Lyman-α absorbers (DLAs) at $$z$$ ∼ 5; the abundance of weak metal absorbers; the ultraviolet background amplitude; and the Lyman-α flux power spectrum at $$z$$ = 5.4. The galaxy stellar mass and ultraviolet luminosity functions are underproduced by ≤2 ×, suggesting an overly vigorous feedback model. The mean transmission in the Lyman-α forest is underproduced at $$z$$ < 6, indicating tension between measurements of the UVB amplitude and Lyman-α transmission. The observed $$\mathrm{Si\, {\small IV}}$$ column density distribution is reasonably well reproduced (∼1σ low). By contrast, $$\mathrm{C\,{\small IV}}$$ remains significantly underproduced despite being boosted by an intense >4 Ryd UVB. Solving this problem by increasing metal yields would overproduce both weak absorbers and DLA metallicities. Instead, the observed strength of high-ionization emission from high-redshift galaxies and absorption from their environments suggest that the ionizing flux from conventional stellar population models is too soft. [ABSTRACT FROM AUTHOR]

We present the first low-frequency Murchison Widefield Array (MWA) radio continuum maps of the Magellanic Clouds (MCs), using mosaics from the GaLactic Extragalactic All-Sky MWA (GLEAM) survey. In this paper, we discuss the overall radio continuum morphology between 76 and 227 MHz and compare them with neutral hydrogen maps, 1.4 GHz continuum maps and optical images. Variation of diffuse emission is noticeable across the Large Magellanic Cloud (LMC) but absent across the bar of the Small Magellanic Cloud (SMC). We also measure the integrated flux densities and derive the spectral indices for the MCs. A double power-law model with fixed α1 = −0.1 fit between 19.7 MHz and 8.55 GHz yields α0 = −0.66 ± 0.08 for the LMC. A power-law model yields $$\alpha _{\rm 8.55 GHz}^{\rm 85.5 MHz} = -0.82\pm 0.03$$ for the SMC. The radio spectral index maps reveal distinctive flat and steep spectral indices for the H  ii regions and supernova remnants, respectively. We find strong correlation between H  ii regions and Hα emission. Using a new 150 MHz–Hα relation as a star formation rate indicator, we estimate global star formation rates of 0.068–0.161 M⊙ yr−1 and 0.021–0.050 M⊙ yr−1 for the LMC and SMC, respectively. Images in 20 frequency bands, and wideband averages are made available via the GLEAM virtual observatory server. [ABSTRACT FROM AUTHOR]

We present Gemini Multi-Object Spectrograph spectra of H  i -rich tidal features located around the outskirts of two interacting galaxy pairs, NGC 3166/9 and NGC 4725/47. These follow-up observations are part of a multiwavelength campaign to study the properties and frequency of tidal dwarf galaxies (TDGs) in group environments. Based on the calculated gas-phase metallicity and redshift, in addition to the previously measured H  i and stellar properties, we have confirmed the tidal origins of TDG candidate AGC 208457, which has emerged from the tidal debris of an interaction between the NGC 3166/9 galaxy pair. By comparing H  i and optical recessional velocities, we have also confirmed a physical association of the gaseous knots and star clusters embedded in the metal-rich tidal tail of NGC 4747. [ABSTRACT FROM AUTHOR]