Column Density Research Articles

Correlations among complex organic molecules around protostars: Effects of physical structure

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 (NH$_2$CHO) to methanol (CH$_3$OH), $N_ NH_2CHO /N_ CH_3OH $, is one of the highest compared to other ratios. The larger scatter for $N_ NH_2CHO /N_ CH_3OH $ (or weak correlation of these two molecules) is sometimes interpreted as evidence of gas-phase formation of NH$_2$CHO. 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 $ gtrsim 2000$\,K larger binding energy than methanol) and the small-scale structure of the envelope and the disk system. Therefore, we do not include chemistry in our models in order to isolate the effect of physical factors. We also include CH$_3$CN in our work as a control molecule, as it has a similar binding energy to CH$_3$OH. We used radiative transfer models to calculate the emission from NH$_2$CHO, CH$_3$OH, and CH$_3$CN in protostellar systems with and without disks. The abundances of these species were parameterized in our models, and we fit the calculated emission lines to find the column densities and excitation temperatures of these species, as done in real observations. Given the difference in binding energies of NH$_2$CHO and CH$_3$OH, we find the gas-phase $N_ NH_2CHO /N_ CH_3OH $ 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., $ sim 2$) for $N_ CH_3CN /N_ CH_3OH $ (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 $N_ NH_2CHO /N_ CH_3OH $, comparable with that of observations. The scatter in $N_ NH_2CHO /N_ CH_3OH $ is larger than that of $N_ CH_3CN /N_ CH_3OH $ in models consistent with the observations. However, the scatter in the models for $N_ CH_3CN /N_ CH_3OH $ is smaller than observations by a factor of around two, as expected from the similar binding energies of CH$_3$OH and CH$_3$CN pointing to the need for some chemical effects in the gas or ice to explain the observed ratios. We show that the scatter in $N_ NH_2CHO /N_ CH_3OH $ will be lower than previously measured if we correct for the difference in sublimation temperatures of these two species in observations of $ sim 40$ protostellar systems with ALMA. The scatter in $N_ NH_2CHO /N_ CH_3OH $ (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 NH$_2$CHO a "normal" molecule. Therefore, we conclude that gas-phase chemistry routes for NH$_2$CHO are not necessary to explain the larger scatter of $N_ NH_2CHO /N_ CH_3OH $ compared with other ratios.

Interannual variability of summertime formaldehyde (HCHO) vertical column density and its main drivers at northern high latitudes

Abstract. The northern high latitudes (50–90° N, mostly including boreal-forest and tundra ecosystems) have been undergoing rapid climate and ecological changes over recent decades, leading to significant variations in volatile organic compounds (VOC) emissions from biogenic and biomass burning sources. Formaldehyde (HCHO) is an indicator of VOC emissions, but the interannual variability of HCHO and its main drivers over the region remains unclear. In this study, we use the GEOS-Chem chemical transport model and satellite retrievals from the Ozone Monitoring Instrument (OMI) and the Ozone Mapping and Profiler Suite (OMPS) to examine the interannual variability of HCHO vertical column density (VCD) during the summer seasons spanning from 2005 to 2019. Our results show that, in 2005–2019 summers, wildfires contributed 75 %–90 % of the interannual variability of HCHO VCD over Siberia, Alaska and northern Canada, while biogenic emissions and background methane oxidation account for ∼ 90 % of HCHO interannual variability over eastern Europe. We find that monthly solar-induced chlorophyll fluorescence (SIF) from the Orbiting Carbon Observatory-2 (OCO-2), an efficient proxy for plant photosynthesis, shows a good linear relationship (R= 0.6–0.7) with the modeled biogenic HCHO column (dVCDBio,GC) in eastern Europe, Siberia, Alaska and northern Canada, indicating the coupling between SIF and biogenic VOC emissions over the four domains on a monthly scale. In Alaska, Siberia and northern Canada, SIF and dVCDBio,GC both show relatively lower interannual variabilities (SIF: CV = 1 %–9 %, dVCDBio,GC: CV = 1 %–2 %; note that CV stands for coefficient of variation) in comparison to wildfire-induced HCHO (CV = 8 %–13 %), suggesting that the high interannual variabilities of OMI HCHO VCD (CV = 10 %–16 %) in these domains are likely driven by wildfires instead of biogenic emissions.

Unveiling the complex circumgalactic medium: A comparative study of merging and non-interacting galaxy groups

Abstract While most galaxies live in group environments where they undergo an accelerated evolution, the characteristics of their circumgalactic medium (CGM) remain uncertain. We present an analysis of the CGM of two galaxy groups in different stages of interaction: (G1) a close pair of galaxies (z = 0.043) separated by 87 kpc that do not show signs of interactions and (G2) four merging galaxies (z = 0.098) separated by 10 kpc. We present spatially-resolved Keck/KCWI galaxy observations and HST/COS quasar spectra (G1 at 48 kpc and G2 at 100 kpc away) to quantify both the resolved galaxy and CGM properties in these two different group environments. G1 contains two typical star-forming galaxies with no evidence of strong outflows. G2 contains two star-forming, one post-starburst and one quiescent galaxy. Both groups have a range of CGM detected metal lines (H i, C ii, Si ii, Si iii, N v and O vi). Despite G2 being twice as far from the quasar, G2 has $\log (N({\rm H\, {\small \rm I} })/{\rm cm}^{-2})=17.33$, compared to $\log (N(\rm H\, {\small \rm I})/{\rm cm}^{-2})=16.43$ for G1. We find that the CGM of the merging galaxies (G2) is more kinematically complex, is in a higher ionisation state, spans a wider range of metallicities and column densities, has smaller cloud sizes, and is inconsistent with the simple superposition model that seems to match well with G1. We conclude that the complexity of the CGM in merging galaxies surpasses that of not strongly interacting galaxies, suggesting that mergers play a significant role in shaping the intricate structure of the CGM.

MHONGOOSE: A MeerKAT nearby galaxy survey

The MHONGOOSE (MeerKAT Observations of Nearby Galactic Objects: Observing Southern Emitters) survey maps the distribution and kinematics of the neutral atomic hydrogen ( gas in and around 30 nearby star-forming spiral and dwarf galaxies to extremely low column densities. The column density sensitivity (3sigma over 16 ranges from $ $ cm$^ $ at $90''$ resolution to $ $ cm$^ $ at the highest resolution of $7''$. The mass sensitivity ($3 over 50 is $ at a distance of 10 Mpc (the median distance of the sample galaxies). The velocity resolution of the data is 1.4 One of the main science goals of the survey is the detection of cold accreting gas in the outskirts of the sample galaxies. The sample was selected to cover a range in masses from $10^7$ to almost in order to optimally sample possible accretion scenarios and environments. The distance to the sample galaxies ranges from 3 to 23 Mpc. In this paper, we present the sample selection, survey design, and observation and reduction procedures. We compared the integrated fluxes based on the MeerKAT data with those derived from single-dish measurement and find good agreement, indicating that our MeerKAT observations are recovering all flux. We present moment maps of the entire sample based on the first ten percent of the survey data, and find that a comparison of the zeroth- and second-moment values shows a clear separation in the physical properties of the between areas with star formation and areas without related to the formation of a cold neutral medium. Finally, we give an overview of the companion and satellite galaxies in the 30 fields, five of which have not previously been cataloged. We find a clear relation between the number of companion galaxies and the mass of the main target galaxy.

Strong damped Lyman-α absorption in young star-forming galaxies at redshifts 9 to 11.

Primordial neutral atomic gas, mostly composed of hydrogen, is the raw material for star formation in galaxies. However, there are few direct constraints on the amount of neutral atomic hydrogen (Hi) in galaxies at early cosmic times. We analyzed James Webb Space Telescope (JWST) near-infrared spectroscopy of distant galaxies, at redshifts ≳8. From a sample of 12 galaxies, we identified three that show strong damped Lyman-α absorption due to Hi in their local surroundings. The galaxies are located at spectroscopic redshifts of 8.8, 10.2, and 11.4, corresponding to 400 to 600 million years after the Big Bang. They have Hi column densities ≳1022 cm-2, which is an order of magnitude higher than expected for a fully neutral intergalactic medium, and constitute a gas-rich population of young star-forming galaxies.

Resolving Red Giant Winds with the Hubble Space Telescope* *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-15903 and GO-15904.

We describe recent spectroscopic observations of red giant stars made by the Space Telescope Imaging Spectrograph (STIS) instrument on board the Hubble Space Telescope, which has provided spatially resolved observations of the warm chromospheric winds that predominate for early K to mid-M giants. The H i Lyα lines of a set of 11 red giants observed with the STIS/E140M echelle grating are first analyzed to ascertain wind H i column densities and total wind mass-loss rates. The M giants have estimated mass-loss rates of Ṁ=(14–86)×10−11 M ⊙ yr−1, while the K giants with detected wind absorption have weaker winds with Ṁ=(1.5–2.8)×10−11 M ⊙ yr−1. We use long-slit spectra of H i Lyα for two particular red giants, α Tau (K5 III) and γ Cru (M3.5 III), to study the spatial extent of the Lyα emission. From these data we estimate limits for the extent of detectable emission, which are r = 193 R * for γ Cru and r = 44 R * for α Tau. The cross-dispersion emission profiles in the STIS echelle spectra of the larger sample of red giants also show evidence for spatial resolution, not only for H i Lyα but for other lines with visible wind absorption, such as Fe ii, Mg ii, Mg i, O i, and C ii. We characterize the nature of these spatial signatures. The spatial extent is far more apparent for the M giants than for the K giants, consistent with the stronger winds found for the M giants from the Lyα analysis.

The transient event in NGC 1566 from 2017 to 2019

Context. NGC 1566 is a local face-on Seyfert galaxy and is known for exhibiting recurrent outbursts that are accompanied by changes in spectral type. The most recent transient event occurred from 2017 to 2019 and was reported to be accompanied by a change in Seyfert classification from Seyfert 1.8 to Seyfert 1.2. Aims. We aim to study the transient event in detail by analyzing the variations in the optical broad-line profiles. In particular, we intend to determine the structure and kinematics of the broad-line region. Methods. We analyzed data from an optical spectroscopic variability campaign of NGC 1566 taken with the 9.2 m Southern African Large Telescope (SALT) between July 2018 and October 2019 triggered by the detection of hard X-ray emission in June 2018. We supplemented this data set with optical to near-infrared (NIR) spectroscopic archival data taken by VLT/MUSE in September 2015 and October 2017, and investigated the emission from different line species during the event. Results. NGC 1566 exhibits pronounced spectral changes during the transient event. We observe the emergence and fading of a strong power-law-like blue continuum as well as strong variations in the Balmer, He I, and He II lines and the coronal lines [Fe VII], [Fe X], and [Fe XI]. Moreover, we detect broad double-peaked emission line profiles of O Iλ8446 and the Ca IIλλ8498, 8542, 8662 triplet. This is the first time that genuine double-peaked O Iλ8446 and Ca IIλλ8498, 8542, 8662 emission in AGN is reported in the literature. All broad lines show a clear redward asymmetry with respect to their central wavelength and we find indications for a significant blueward drift of the total line profiles during the transient event. The profiles and the FWHM of the Balmer lines remain largely constant during all observations. We show that the double-peaked emission line profiles are well approximated by emission from a low-inclination, relativistic eccentric accretion disk, and that single-peaked profiles can be obtained by broadening due to scale-height-dependent turbulence. Small-scale features in the O I and Ca II lines suggest the presence of inhomogeneities in the broad-line region. Conclusions. We conclude that the broad-line region in NGC 1566 is dominated by the kinematics of a relativistic eccentric accretion disk. The broad-line region can be modeled to be vertically stratified with respect to scale-height turbulence with O I and Ca II being emitted close to the disk in a region with high (column) density, while the Balmer and helium lines are emitted at greater scale height above the disk. The observed blueward drift might be attributed to a low-optical-depth wind launched during the transient event. Except for this wind, the observed kinematics of the broad-line region remain largely unchanged during the transient event.

Bayesian analysis of the molecular emission and dust continuum of protoplanetary disks

The MIRI instrument on board the James Webb Space Telescope probes the chemistry and dust mineralogy of the inner regions of protoplanetary disks. The observed spectra are unprecedented in their detail and reveal a rich chemistry with strong diversity between objects. This complicates interpretations that are mainly based on manual continuum subtraction and 0D slab models. We investigate the physical conditions under which the gas emits in protoplanetary disks. Based on MIRI spectra, we apply a full Bayesian analysis that provides the posterior distributions of dust and molecular properties, such as column densities and emission temperatures. To do so, we introduced the Dust Continuum Kit with Line emission from Gas (DuCKLinG), a Python-based model simultaneously describing the molecular line emission and the dust continuum of protoplanetary disks without large computational cost. The model describes the dust continuum emission by dust models with precomputed dust opacities. The molecular emission is based on LTE slab models but from extended radial ranges with gradients in column densities and emission temperatures. We compare the model to observations using Bayesian analysis with linear regression techniques to reduce the dimension of the parameter space. We benchmarked this model to a complex thermo-chemical ProDiMo model of AA\,Tau and fit the MIRI spectrum of GW\,Lup. The latter allowed for a comparison to the previous results obtained with single slab models and hand-fitted continuum. We successfully decrease the computational time of the fitting method by a factor of $80$ by eliminating linear parameters, such as the emission areas, from the Bayesian run. This approach does not significantly change the retrieved molecular parameters, and only the calculated errors on the optically thin dust masses slightly decrease. For an AA\,Tau ProDiMo mock observation, we find that the retrieved molecular conditions from DuCKLinG (column densities from $3 cm^ $ to $4 cm^ $, radial range from $0.2\ au $ to $1.2\ au $, and temperature range from about $200\ K $ to $400\ K $) fall within the true values from ProDiMo (column densities between $4 cm^ $ to $5 cm^ $, radial extent $0.1\ au $ to $6.6\ au $, and temperature range from about $120\ K $ to $1000\ K $). The smaller DuCKLinG ranges can be explained by the relative flux contributions of the different parts of ProDiMo. The parameter posterior of GW\,Lup reinforces previously found results. The previously determined column densities fall within the retrieved ranges in this study for all examined molecules ( CO2 H2O HCN and C2H2 ). Similar overlap is found for the temperatures with only the temperature range of HCN (from $570^ K$ to K$) not including the previously found value ($875\ K$). This discrepancy may be due to the simultaneous fitting of all molecules compared to the step-by-step fitting of the previous study. There is statistically significant evidence for radial temperature and column density gradients for H2O and CO2 compared to the constant temperature and column density assumed in the 0D slab models. Additionally HCN and C2H2 emit from a small region with near constant conditions. Due to the small selected wavelength range $13.6\ m$ to $16.3\ m$, the dust properties are not well constrained for GW\,Lup. DuCKLinG can become an important tool to analyse the molecular emission and dust mineralogy of large samples based on JWST/MIRI spectra in an automated way.

Merging filaments II: The origin of the tuning fork

Abstract We suggest that filaments in star-forming regions undergo frequent mergers. As stellar nurseries, filaments play a vital role in understanding star formation and mergers could pave the way for understanding the formation of more complex filamentary systems, such as networks and hubs. We compare the physical properties derived from hydrodynamic RAMSES simulations of merging filaments to those obtained from ALMA observations towards the LDN 1641-North region in Orion. We find similarities in the distributions of line-mass, column density and velocity dispersion. Such common features support the hypothesis of filament mergers shaping the structure of the interstellar medium.

The Scatter Matters: Circumgalactic Metal Content in the Context of the M–σ Relation

The interaction between supermassive black hole (SMBH) feedback and the circumgalactic medium (CGM) continues to be an open question in galaxy evolution. In our study, we use smoothed particle hydrodynamics simulations to explore the impact of SMBH feedback on galactic metal retention and the motion of metals and gas into and through the CGM of L* galaxies. We examine 140 galaxies from the 25 Mpc cosmological volume Romulus25, with stellar masses between log(M */M ⊙) = 9.5–11.5. We measure the fraction of metals remaining in the interstellar medium (ISM) and CGM of each galaxy and calculate the expected mass of each SMBH based on the M BH–σ relation (Kormendy & Ho 2013). The deviation of each SMBH from its expected mass, ΔM BH, is compared to the potential of its host via σ. We find that SMBHs with accreted mass above M BH–σ are more effective at removing metals from the ISM than undermassive SMBHs in star-forming galaxies. Overall, overmassive SMBHs suppress the total star formation of their host galaxies and more effectively move metals from the ISM into the CGM. However, we see little to no evacuation of gas from the CGM out of their halos, in contrast with other simulations. Finally, we predict that C iv column densities in the CGM of L* galaxies are unlikely to depend on host galaxy SMBH mass. Our results show that the scatter in the low-mass end of the M BH–σ relation may indicate how effective an SMBH is in the local redistribution of mass in its host galaxy.

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

Episodic accretion in protostars leads to luminosity outbursts that end up heating their surroundings. This rise in temperature pushes the snow lines back, enabling the desorption of chemical species from dust grain surfaces, which may significantly alter the chemical history of the accreting envelope. However, a limited number of extensive chemical surveys of eruptive young stars have been performed thus far. In the present study, we carry out a large spectral survey of the binary Class I protostar L1551 IRS 5, known to be a FUor-like object, in the 3mm and 2mm bands with the IRAM-30m telescope. As a result, we detected more than 400 molecular lines. The source displays a great chemical richness with the detection of 75 species, including isotopologues. Among these species, there are 13 hydrocarbons, 25 N-bearing species, 30 O-bearing species, 15 S-bearing species, 12 deuterated molecules, and a total of 10 complex organic molecules (l-C$_4$H$_2$, CH$_3$CCH, CH$_2$DCCH, CH$_3$CHO, CH$_3$CN, CH$_3$OCH$_3$, CH$_3$OCHO, CH$_3$OH, CH$_2$DOH, and HC$_5$N). With the help of local thermodynamic equilibrium (LTE) and non-LTE models, we determined the column densities of most molecules as well as excitation and kinetic temperatures. While most of those molecules trace the cold envelope ($ 20$ K), the OCS and CH$_3$OH emission arise from the warm ($> 100$ K) innermost ($< 2$ regions. We compared the chemical inventory of L1551 IRS 5 and its column density ratios, including isotopic ratios, with other protostellar sources. A broad chemical diversity is seen among Class I objects. More observations with both single-dish telescopes and interferometers are needed to characterize the diversity in a larger sample of protostars, while more astrochemical models would help explain this diversity, in addition to the impact of luminosity outbursts on the chemistry of protostellar envelopes.

Molecular cloud matching in CO and dust in M33. I. High-resolution hydrogen column density maps from Herschel

This study is aimed to contribute to a more comprehensive understanding of the molecular hydrogen distribution in the galaxy M33 by introducing novel methods for generating high angular resolution ($18.2''$, equivalent to $75\ pc $ for a distance of $847\ kpc $) column density maps of molecular hydrogen ($N_ H_2 $). M33 is a local group galaxy that has been observed with Herschel in the far-infrared (FIR) wavelength range from $70$ to $500\ Previous studies have presented total hydrogen column density maps ($N_ H $), using these FIR data (partly combined with mid-IR maps), employing various methods. We first performed a spectral energy distribution (SED) fit to the $160$, $250$, $350,$ and $500\ continuum data obtain $N_ H $, using a technique similar to one previously reported in the literature. We also use a second method which involves translating only the $250\ map into a $N_ H $ map at the same angular resolution of $18.2''$. An $N_ H_2 $ map via each method is then obtained by subtracting the component. Distinguishing our study from previous ones, we adopt a more versatile approach by considering a variable emissivity index, $ and dust absorption coefficient, $ This choice enables us to construct a $ map, thereby enhancing the depth and accuracy of our investigation of the hydrogen column density. We address the inherent biases and challenges within both methods (which give similar results) and compare them with existing maps available in the literature. Moreover, we calculate a map of the carbon monoxide $ CO(1-0) $-to-molecular hydrogen (htwo ) conversion factor ( factor), which shows a strong dispersion around an average value of $1.8 throughout the disk. We obtain column density probability distribution functions ($N$-PDFs) from the $N_ H $, $N_ H_2 $, and $N_ hi $ maps and discuss their shape, consisting of several log-normal and power-law tail components.

Evidence of Pop III stars' chemical signature in neutral gas at z ~ 6. A study based on the E-XQR-30 spectroscopic sample

This study explores the metal enrichment signatures attributed to the first generation of stars (Pop III) in the Universe, focusing on the E-XQR-30 sample -- a collection of 42 high signal-to-noise ratio spectra of quasi-stellar objects (QSOs) with emission redshifts ranging from 5.8 to 6.6. We aim to identify traces of Pop III metal enrichment by analyzing neutral gas in the interstellar medium of primordial galaxies and their satellite clumps, detected in absorption. To chase the chemical signature of Pop III stars, we studied metal absorption systems in the E-XQR-30 sample, selected through the detection of the neutral oxygen absorption line at 1302 The line is a reliable tracer of neutral hydrogen and allowed us to overcome the challenges posed by the Lyman-alpha forest's increasing saturation at redshifts above $ to identify damped Lyman-alpha systems (DLAs). We detected and analyzed 29 systems at $z 5.4$, differentiating between proximate DLAs (PDLAs) and intervening DLAs. Voigt function fits were applied to obtain ionic column densities, and relative chemical abundances were determined for 28 systems. These were then compared with the predictions of theoretical models. Our findings expand the study of systems at $z 5.4$ fourfold. No systematic differences were observed in the average chemical abundances between PDLAs and intervening DLAs. The chemical abundances in our sample align with literature systems at $z > 4.5$, suggesting a similar enrichment pattern for this class of absorption systems. A comparison between these DLA-analogs at $4.5 < z < 6.5$ with a sample of very metal-poor DLAs at $2 < z < 4.5$ shows in general similar average values for the relative abundances, with the exception of C/O Si/Fe and Si/O which are significantly larger for the high-$z$ sample. Furthermore, the dispersion of the measurements significantly increases in the high-redshift bin. This increase is predicted by the theoretical models and indicates a potential retention of Pop III signatures in the probed gas. This work represents a significant advancement in the study of the chemical properties of highly neutral gas at $z 5.4$, shedding light on its potential association with the metal enrichment from Pop III stars. Future advancements in observational capabilities, specifically high-resolution spectrographs, are crucial for refining measurements and addressing current limitations in the study of these distant absorption systems.

ALMA-IMF XII: Point-process mapping of 15 massive protoclusters

A crucial aspect in addressing the challenge of measuring the core mass function (CMF), that is pivotal for comprehending the origin of the initial mass function (IMF), lies in constraining the temperatures of the cores. We aim to measure the luminosity, mass, column density and dust temperature of star-forming regions imaged by the ALMA-IMF large program. These fields were chosen to encompass early evolutionary stages of massive protoclusters. High angular resolution mapping is required to capture the properties of protostellar and pre-stellar cores within these regions, and to effectively separate them from larger features, such as dusty filaments. We employed the point process mapping (PPMAP) technique, enabling us to perform spectral energy distribution fitting of far-infrared and submillimeter observations across the 15 ALMA-IMF fields, at an unmatched 2.5$^ prime $ angular resolution. By combining the modified blackbody model with near-infrared data, we derived bolometric luminosity maps. We estimated the errors impacting values of each pixel in the temperature, column density, and luminosity maps. Subsequently, we employed the extraction algorithm getsf on the luminosity maps in order to detect luminosity peaks and measure their associated masses. We obtained high-resolution constraints on the luminosity, dust temperature, and mass of protoclusters, that are in agreement with previously reported measurements made at a coarser angular resolution. We find that the luminosity-to-mass ratio correlates with the evolutionary stage of the studied regions, albeit with intra-region variability. We compiled a PPMAP source catalog of 313 luminosity peaks using getsf on the derived bolometric luminosity maps. The PPMAP source catalog provides constraints on the mass and luminosity of protostars and cores, although one source may encompass several objects. Finally, we compare the estimated luminosity-to-mass ratio of PPMAP sources with evolutionary tracks and discuss the limitations imposed by the 2.5$^ prime $ beam.

Unexpected HCHO transnational transport: influence on the temporal and spatial distribution of HCHO in Tibet from 2013 to 2021 based on satellite

Formaldehyde (HCHO) is a serious hazardous air pollutant and crucial precursor of PM2.5 and ozone compound pollution. There has been a dearth of HCHO research in Tibet where pressing need to protect the unique ecosystem. Therefore, this study aims to investigate the spatial-temporal distribution of HCHO from 2013 to 2021 and identify its influencing factors using satellite observations. Our findings reveal a noteworthy annual growth rate of 2.25% yr−1 in HCHO vertical column density (VCD) in Tibet. This rate is comparable to that in India and even surpasses levels observed in many other regions worldwide, including eastern China. Furthermore, unlike other areas, the eastern region of Tibet exhibits no discernible seasonal pattern in HCHO VCD. The anomalous variation in HCHO concentrations in Tibet can primarily be attributed to long-distance transnational transport originating from incomplete combustion in India Assam. Our research underscores the urgent need for enhanced atmospheric environmental management in Tibet.

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

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

Introducing two improved methods for approximating radiative cooling in hydrodynamical simulations of accretion discs

ABSTRACT The evolution of many astrophysical systems depends strongly on the balance between heating and cooling, in particular star formation in giant molecular clouds and the evolution of young protostellar systems. Protostellar discs are susceptible to the gravitational instability, which can play a key role in their evolution and in planet formation. The strength of the instability depends on the rate at which the system loses thermal energy. To study the evolution of these systems, we require radiative cooling approximations because full radiative transfer is generally too expensive to be coupled to hydrodynamical models. Here, we present two new approximate methods for computing radiative cooling that make use of the polytropic cooling approximation. This approach invokes the assumption that each parcel of gas is located within a spherical pseudo-cloud, which can then be used to approximate the optical depth. The first method combines the methods introduced by Stamatellos et al. and Lombardi et al. to overcome the limitations of each method at low and high optical depths, respectively. The second method, the ‘modified Lombardi’ method, is specifically tailored for self-gravitating discs. This modifies the scale height estimate from the method of Lombardi et al. using the analytical scale height for a self-gravitating disc. We show that the modified Lombardi method provides an excellent approximation for the column density in a fragmenting disc, a regime in which the existing methods fail to recover the clumps and spiral structures. We therefore recommend this improved radiative cooling method for more realistic simulations of self-gravitating discs.

Toward a direct measurement of the cosmic acceleration: The pilot observation of HI 21cm absorption line at FAST

Abstract In this study, we present findings on the detection of neutral atomic hydrogen (HI) 21cm absorption in the spectrum of PKS1413+135 at redshift $z=0.24670041$. The observations were conducted by FAST, with a spectral resolution of 10 Hz, using 10 minutes of observing time.The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10kHz within a 2MHz bandwidth. The goal is to determine the rate of the latest cosmic acceleration by directly measuring the evolution of the redshift of HI 21cm absorption line with Hubble flow towards a common background Quasar over a decade or longer time span. This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift $z < 1$, specifically redshift drift $\dot{z}$ or the SL effect.The measured HI gas column density in this DLA system is approximately equivalent to the initial observation value, considering uncertainties in the spin temperature of a spiral host galaxy. The high signal-to-noise ratio of 57, obtained at a 10kHz resolution, strongly supports the feasibility of using the HI 21cm absorption line in DLA systems to accurately measure the redshift rate at a precision level of around $10^{-10}$ per decade.

The rotation-tunneling spectrum of 3-hydroxypropenal and confirmation of its detection toward IRAS 16293-2422 B

3-Hydroxypropenal (HOCHCHCHO) is the lower energy tautomer of malonaldehyde which displays a complex rotation-tunneling spectrum. It was detected somewhat tentatively toward the solar-type protostellar system IRAS 16293$-$2422 with ALMA in the framework of the Protostellar Interferometric Line Survey (PILS). Several transitions, however, had large residuals, preventing not only their detection, but also the excitation temperature of the species from being determined unambiguously. We want to extend the existing rotational line list of 3-hydroxypropenal to shed more light on the recent observational results and to facilitate additional radio astronomical searches for this molecule. We recorded and analyzed the rotation-tunneling spectrum of 3-hydroxypropenal in the frequency regions between 150 and 330 GHz and between 400 and 660 GHz. Transitions were searched for in the PILS observations of IRAS 16293$-$2422. Local thermodynamic equilibrium (LTE) models were carried out and compared to the observations to constrain the excitation temperature. Additional transitions were searched for in other ALMA archival data of the same source to confirm the presence of 3-hydroxypropenal. More than 7500 different spectral lines, corresponding to more than 11500 transitions, were assigned in the course of our investigation with quantum numbers $2 J 100$, $K_a 59$, and $K_c 97$, resulting in a greatly improved set of spectroscopic parameters. The comparison between the LTE models and the observations yields an excitation temperature of 125 K with a column density $N = 1.0 $ cm$^ $ for this species. We identified seven additional lines of 3-hydroxypropenal that show a good agreement with the model in the ALMA archive data. The calculated rotation-tunneling spectrum of 3-hydroxypropenal has sufficient accuracy for radio astronomical searches. With the solution of the excitation temperature conundrum and the detection of seven more lines, we consider the detection of 3-hydroxypropenal toward IRAS 16293$-$2422 as secure.

Laboratory and astronomical discovery of cyanothioketene, NCCHCS, in the cold starless core TMC-1

We present the detection of cyanothioketene, NCCHCS, in the laboratory and toward TMC-1. This transient species was produced through a discharge of a gas mixture of CH$_2$CHCN and CS$_2$ using argon as carrier gas, and its rotational spectrum between 9 and 40 GHz was characterized using a Balle-Flygare narrowband-type Fourier-transform microwave spectrometer. A total of 21 rotational transitions were detected in the laboratory, all of them exhibiting hyperfine structure induced by the spin of the N nucleus. The spectrum for NCCHCS was predicted in the domain of our line surveys using the derived rotational and distortion constants. The detection in the cold starless core TMC-1 was based on the QUIJOTE$^1$ line survey performed with the Yebes 40m radio telescope. Twenty-three lines were detected with $K_a$=0, 1, and 2 and $J_u$=9 up to 14. The derived column density is (1.2pm 0.1)times 1011 cm$^ $ for a rotational temperature of 8.5pm 1\,K. The abundance ratio of thioketene and its cyano derivative, H$_2$CCS/NCCHCS, is 6.5pm 1.3. Although ketene is more abundant than thioketene by sim 15 times, its cyano derivative NCCHCO surprisingly is not detected with a 3sigma upper level to the column density of 3.0times 1010 $, which results in an abundance ratio H$_2$CCO/NCCHCO \,$>$\,430. Hence, the chemistry of CN derivatives seems to be more favored for S-bearing than for O-bearing molecules. We carried out chemical modeling calculations and found that the gas-phase neutral-neutral reactions CCN + H$_2$CS and CN + H$_2$CCS could be a source of NCCHCS in TMC-1.