Molecular Clouds Research Articles

Mutual neutralization of C_60^+ and C_60^- ions. Excitation energies and state-selective rate coefficients

Mutual neutralization (MN) between cations and anions plays an important role in determining the charge balance in certain astrophysical environments. However, empirical data for such reactions involving complex molecular species have been lacking due to challenges in performing experimental studies, leaving the astronomical community to rely on decades-old models with large uncertainties for describing these processes in the interstellar medium. Our aim is to investigate the MN reaction C$_ ^+$ + C$_ ^-$ rightarrow C$_ ^*$ + C$_ $ for collisions at interstellar-like conditions. We studied the MN reaction between C$_ ^+$ and C$_ ^-$ at collision energies of 100\,meV using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) and its merged beam capabilities. To aid in the interpretation of the experimental results, semiclassical modeling based on the Landau-Zener approach was performed for the studied reaction. We experimentally identified a narrow range of kinetic energies for the neutral reaction products. Modeling was used to calculate the quantum state-selective reaction probabilities, absolute cross sections, and rate coefficients of these MN reactions, using the experimental results as a benchmark. We compared the MN cross sections with model results for electron attachment to C$_ $ and electron recombination with C$_ Our results show that it is crucial to take mutual polarization effects, the finite sizes, and the final quantum states of both molecular ions into account in order to obtain reliable predictions of MN rates expected to strongly influence the charge balance and chemistry in environments such as dense molecular clouds.

The Foundations of Multi-line Molecular Cloud Population Synthesis

Abstract While galactic molecular clouds have been studied in great detail, the spatial resolution of current single-dish radio telescopes inhibits our ability to resolve individual molecular clouds in external galaxies. In this case, the line luminosity signal received is an average over a ≥100 pc diameter beam containing several molecular clouds. This leads us to an interesting question: If we point the telescope beam at a region of molecular clouds in a nearby galaxy, can we meaningfully decompose the unresolved signal we receive? In this work, we formulate theoretical methods of decomposing a galaxy line luminosity signal into its cloud population line luminosity components.

Cosmic-ray ionization of low-excitation lines in active galactic nuclei and starburst galaxies

Cosmic rays (CRs) can significantly impact dense molecular clouds in galaxies, heating the interstellar medium (ISM) and altering its chemistry, ionization, and thermal properties. Their influence is particularly relevant in environments with high CR rates, such as starburst galaxies with supernova remnants or jets and outflows in active galactic nuclei (AGN). CRs also transfer substantial energy to the ionized phase of the ISM far from the ionization source, preventing gas cooling and driving large-scale winds. In this work, we use Cloudy photoionization models to investigate the effect of CRs on nebular gas which is an area of study that remains relatively under-explored, mainly focusing on cold molecular gas. Our models cover a broad range of density ($1$ to $10^4\ cm^ $), ionization parameter ($-3.5 U -1.5$), and CR ionization rate s^ $ to $10^ s^ $). These are compared to VLT/MUSE observations of two prototypical AGN, Centaurus A (radio-loud) and NGC 1068 (radio-quiet), and the starburst NGC 253. We find that high CR rates ($ s^ $) typical of AGN and strong starburst galaxies can significantly alter the thermal structure of the ionized gas by forming a deep secondary low-ionization layer beyond the photoionization-dominated region. This enhances emission from low-ionization transitions, such as N ii lambda 6584 S ii and O i lambda 6300 affecting classical line-ratio diagnostics, metallicity, and ionization estimates. Unlike pure photoionization models, AGN simulations with high CR ionization rates reproduce the Seyfert loci in Baldwin, Phillips, and Terlevich (BPT) diagrams without requiring supersolar metallicities for the narrow-line region. Additionally, star-formation simulations with high CR ionization rates can explain line ratios in the LINER domain. We propose new maximum starburst boundaries for BPT diagrams in order to distinguish regions dominated by AGN photoionization from those that could be explained by star formation in conjunction with high CR ionization rates.

Tracing hierarchical star formation out to kiloparsec scales in nearby spiral galaxies with UVIT

abstract Molecular clouds fragment under the action of supersonic turbulence and gravity, which results in a scale-free hierarchical distribution of star formation within galaxies. Recent studies suggest that the hierarchical distribution of star formation in nearby galaxies shows a dependence on host galaxy properties. In this context, we study the hierarchical distribution of star formation from a few tens of parsecs up to several kiloparsecs in four nearby spiral galaxies: NGC 1566, NGC 5194, NGC 5457, and NGC 7793, by leveraging large-field-of-view and high-resolution far-ultraviolet (FUV) and near-ultraviolet (NUV) observations from the UltraViolet Imaging Telescope (UVIT). Using the two-point correlation function, we infer that the young star-forming clumps (SFCs) in the galaxies are arranged in a fractal-like hierarchical distribution, but only up to a maximum scale. This largest scale of hierarchy ($l_ corr $) is ubiquitous in all four galaxies and ranges from 0.5 kpc to 3.1 kpc. The flocculent spiral NGC 7793 has roughly five times smaller $l_ corr $ than the other three grand design spirals, possibly due to its lower mass, lower pressure environment, and a lack of strong spiral arms. $l_ corr $ being much smaller than the galaxy size suggests that the star formation hierarchy does not extend to the full galaxy size and it is likely an effect set by multiple physical mechanisms in the galaxy. The hierarchical distribution of SFCs dissipates almost completely within 10$-$50 Myr in our galaxy sample, signifying the migration of SFCs away from their birthplaces with increasing age. The fractal dimension of the hierarchy for our galaxies is found to be between 1.05 and 1.50. We also find that depending upon the star formation environment, significant variations can exist in the local and global hierarchy parameters of a galaxy. Overall, our results suggest that the global hierarchical properties of star formation in galaxies are not universal. This study also demonstrates the capabilities of UVIT in characterising the star formation hierarchy in nearby galaxies. In the future, a bigger sample can be employed to better understand the role of large-scale galaxy properties such as morphology and environment as well as physical processes like feedback, turbulence, shear, and interstellar medium conditions in determining the non-universal hierarchical properties of star formation in galaxies. abstract

First detection of a deuterated molecule in a starburst environment within NGC 253

Deuterium was primarily created during the Big Bang nucleosynthesis. This fact, alongside its fractionation reactions resulting in enhanced abundances of deuterated molecules, means that deuterium abundances can be used to better understand many processes within the interstellar medium as well as its history. Previously, observations of deuterated molecules have been limited to the Galaxy, the Magellanic Clouds, and (with respect to HD) to quasar absorption spectra. We present the first robust detection of a deuterated molecule in a starburst environment and, apart from HD, the first one detected outside the Local Group. As such, we could constrain the deuterium fractionation as observed by DCN. We observed the central molecular zone (CMZ) of the nearby starburst galaxy NGC 253 covering multiple giant molecular clouds (GMCs) with cloud scale observations ($ 30$ pc) using the Atacama Large Millimeter/submillimeter Array. Via the MADCUBA package, we were able to perform local thermodynamic equilibrium analysis in order to obtain deuterium fractionation estimates. We detected DCN in the nuclear region of the starburst galaxy NGC 253 and estimated the deuterium fractionation (D/H ratio) of DCN within the GMCs of the CMZ of NGC 253. We found a range of $5 $ to $10 $, which is relatively similar to the values observed in warm galactic star-forming regions. We also determined an upper limit of D/H of $8 $ from DCO within one region, closer to the cosmic value of D/H. Our observations of deuterated molecules within NGC 253 appear to be consistent with previous galactic studies of star-forming regions. This implies that warmer gas temperatures increase the abundance of DCN relative to other deuterated species. This study also further expands the regions, particularly in the extragalactic domain, in which deuterated species have been detected.

The Impact of Shear on Disk Galaxy Star Formation Rates

Abstract Determining the physical processes that control galactic-scale star formation rates is essential for an improved understanding of galaxy evolution. The role of orbital shear is currently unclear, with some models expecting reduced star formation rates and efficiencies with increasing shear, e.g., if shear stabilizes gas against gravitational collapse, while others predicting enhanced rates, e.g., if shear-driven collisions between giant molecular clouds trigger star formation. Expanding on the analysis of 16 galaxies by C. Suwannajak et al., we assess the shear dependence of star formation efficiency (SFE) per orbital time (ϵ orb) in 49 galaxies selected from the PHANGS-ALMA survey. In particular, we test a prediction of the shear-driven giant molecular cloud​​​​​​ (GMC) collision model that ϵ orb ∝ (1–0.7β), where β ≡ d ln v circ / d ln r , i.e., SFE per orbital time declines with decreasing shear. We fit the function ϵ orb = ϵ orb,0(1 − α CC β) finding α CC ≃ 0.76 ± 0.16; an alternative fit with ϵ orb normalized by the median value in each galaxy yields α CC * = 0.80 ± 0.15 . These results are in good agreement with the prediction of the shear-driven GMC collision theory. We also examine the impact of a galactic bar on ϵ orb finding a modest decrease in SFE in the presence of a bar, which can be attributed to lower rates of shear in these regions. We discuss the implications of our results for the GMC life cycle and environmental dependence of star formation activity.

High-resolution observations of 12CO and 13CO J = 3 → 2 towards the NGC 6334 extended filament

NGC 6334 is a giant molecular cloud (GMC) complex that exhibits elongated filamentary structure and harbours numerous OB-stars, H II regions, and star-forming clumps. To study the emission morphology and velocity structure of the gas in the extended NGC 6334 region using high-resolution molecular line data, we made observations of the 12CO and 13CO J = 3 → 2 lines with the LAsMA instrument at the APEX telescope. The LAsMA data provided a spatial resolution of 20″ (~0.16 pc) and sensitivity of 0.4 K at a spectral resolution of 0.25 km s−1. Our observations revealed that gas in the extended NGC 6334 region exhibits connected velocity coherent structure over ~80 pc parallel to the Galactic plane. The NGC 6334 complex has its main velocity component at approximately −3.9 km s−1 with two connected velocity structures at velocities approximately −9.2 km s−1 (the ‘bridge’ features) and −20 km s−1 (the northern filament, NGC 6334-NF). We observed local velocity fluctuations at smaller spatial scales along the filament that are likely tracing local density enhancement and infall, while the broader V-shaped velocity fluctuations observed towards the NGC 6334 central ridge and G352.1 region located in the eastern filament EF1 indicate globally collapsing gas onto the filament. We investigated the 13CO emission and velocity structure around 42 WISE H II regions located in the extended NGC 6334 region and found that most H II regions show signs of molecular gas dispersal from the centre (36 of 42) and intensity enhancement at their outer radii (34 of 42). Furthermore most H II regions (26 of 42) are associated with least one ATLASGAL clump within or just outside of their radii, the formation of which may have been triggered by H II bubble expansion. Typically towards larger H II regions we found visually clear signatures of bubble shells emanating from the filamentary structure. Overall the NGC 6334 filamentary complex exhibits sequential star formation from west to east. Located in the west, the GM-24 region exhibits bubbles within bubbles and is at a relatively evolved stage of star formation. The NGC 6334 central ridge is undergoing global gas infall and exhibits two gas bridge features possibly connected to the cloud-cloud collision scenario of the NGC 6334-NF and the NGC 6334 main gas component. The relatively quiescent eastern filament (EF1 - G352.1) is a hub-filament in formation, which shows the kinematic signature of global gas infall onto the filament. Our observations highlight the important role of H II regions in shaping the molecular gas emission and velocity structure as well as the overall evolution of the molecular filaments in the NGC 6334 complex.

Filament Accretion and Fragmentation in the Perseus Molecular Cloud

Observations suggest that filaments in molecular clouds can grow by mass accretion while forming cores via fragmentation. Here, we present one of the first large-sample studies of filament accretion using velocity gradient measurements of star-forming filaments on the ∼0.05 pc scale with NH3 observations of the Perseus Molecular Cloud, primarily obtained as a part of the Green Bank Ammonia Survey. In this study, we find significant correlations between the velocity gradient, velocity dispersion, mass per unit length, and number of cores per unit length of the Perseus filaments. Our results suggest a scenario in which filaments not only grow through mass accretion, but also form new cores continuously in the process, well into the thermally supercritical regime. Such behavior is contrary to that expected from isolated filament models but consistent with how filaments form within a more realistic cloud environment, suggesting that the cloud environment plays a crucial role in shaping core formation and evolution in filaments. Furthermore, even though velocity gradients within filaments are not oriented randomly, we find no correlation between velocity gradient orientation and the filament properties we analyzed. This result suggests that gravity is unlikely to be the dominant mechanism imposing order on the ∼0.05 pc scale for dense star-forming gas.

PRODIGE – envelope to disk with NOEMA

Context. The formation of stars has been subject to extensive studies in the past decades on scales from molecular clouds to proto-planetary disks. It is still not fully understood how the surrounding material in a protostellar system, which often shows asymmetric structures with complex kinematic properties, feeds the central protostar(s) and their disk(s). Aims. We study the spatial morphology and kinematic properties of the molecular gas surrounding the IRS3A and IRS3B protostellar systems in the L1448N region located in the Perseus molecular cloud. Methods. We present 1 mm Northern Extended Millimeter Array (NOEMA) observations of the large program PROtostars & DIsks: Global Evolution (PRODIGE). We analyzed the kinematic properties of molecular lines. Because the spectral profiles are complex, the lines were fit with up to three Gaussian velocity components. The clustering algorithm called density-based spatial clustering of applications with noise (DBSCAN) was used to disentangle the velocity components in the underlying physical structure. Results. We discover an extended gas bridge (≈3000 au) surrounding both the IRS3A and IRS3B systems in six molecular line tracers (C18O, SO, DCN, H2CO, HC3N, and CH3OH). This gas bridge is oriented in the northeast-southwest direction and shows clear velocity gradients on the order of 100 km s−1 pc−1 toward the IRS3A system. We find that the observed velocity profile is consistent with analytical streamline models of gravitational infall toward IRS3A. The high-velocity C18O (2-1) emission toward IRS3A indicates a protostellar mass of ≈1.2 M⊙. Conclusions. While high angular resolution continuum data often show IRS3A and IRS3B in isolation, molecular gas observations reveal that these systems are still embedded within a large-scale mass reservoir, whose spatial morphology and velocity profiles are complex. The kinematic properties of the extended gas bridge are consistent with gravitational infall toward the protostar IRS3A.

Pulsational mode stability in complex EiBI-gravitating polarized astroclouds with (r,q)-distributed electrons

The pulsational mode of gravitational collapse (PMGC) originating from the combined gravito-electrostatic interaction in complex dust molecular clouds (DMCs) is a canonical mechanism leading to the onset of astronomical structure formation dynamics. A generalized semi-analytic model is formulated to explore the effects of the Eddington-inspired Born-Infeld (EiBI) gravity, non-thermal (r,q)-distributed electrons, and dust-polarization force on the PMGC stability concurrently. The thermal ions are treated thermo-statistically with the Maxwellian distribution law and the non-thermal electrons with the (r,q)-distribution law. The constitutive partially ionized dust grains are modeled in the fluid fabric. A spherical normal mode analysis yields a generalized linear PMGC dispersion relation. Its oscillatory and propagation characteristics are investigated in a judicious numerical platform. It is found that an increase in the polarization force and positive EiBI parameter significantly enhances the instability, causing the DMC collapse and vice versa. The electron non-thermality spectral parameters play as vital stabilizing factors, and so on. Its reliability and applicability are finally outlined in light of astronomical predictions previously reported in the literature.

Assessing the accuracy of star formation rate measurements by direct star count in molecular clouds

Assessing the accuracy of star formation rate measurements by direct star count in molecular clouds

Molecular Clouds in the Outer Milky Way Disk: Sample, Integrated Properties, and Radial Trends with Galactocentric Radius

We present a catalog of 32,162 12CO molecular clouds that covers the northern outer Galactic plane (l = [15°, 165°] and l = [195°, 230°], and b = [−5.°25, +5.°25]). The catalog was produced using a DBSCAN algorithm applied to the Milky Way Imaging Scroll Painting project data. We systematically analyze both the integrated properties and scaling relationships of these molecular clouds across different Galactocentric radii (8 < R GC < 26 kpc). An interesting finding is that each cloud property’s mean, median, and maximum values generally decrease systematically with increasing R GC, approximated quantitatively by exponential functions. The mass and size spectra for the entire sample show power-law indices of γ = −2.00 ± 0.13 and an upper mass limit of M 0 = (4.5 ± 2.8) × 106 M ⊙, and γ = −3.68 ± 0.48 with an upper size limit of R 0 = 144 ± 80 pc, respectively. These spectra exhibit steeper slopes and reduced upper limits as R GC increases. The derived scaling relations are M=12.00Reff2.41±0.003 , σv=0.25Reff0.66±0.003 , and α vir = 37.2M −0.40 ± 0.002 for the whole outer Galaxy clouds. These scaling relations show slightly steeper correlations observed in more distant locations and notably deviate from Larson’s relations. We find that 44.3% of the molecular mass resides in gravitationally bound structures, a proportion significantly higher than systematic studies from the CfA survey and external galaxies. Moreover, comparisons among different R GC subsamples also reveal a decrease in the amount of bound mass with increasing R GC. The scale length of the molecular disk is estimated to be approximately 2 kpc. These results, based on a constant CO conversion factor of XCO=2.0×1020cm−2Kkms−1−1 , may be slightly altered by variations in X CO. In summary, our findings provide robust evidence for the influence of Galactic evolution on molecular cloud properties, at least in the outer Galaxy region studied.

Triggered and dispersed under feedback of super H ii region W4

The W3/4 Giant Molecular Cloud (GMC) was an ideal target to study the impact of H ii regions onto the surrounding molecular gas and star formation. We utilized PMO CO (1--0) data from the Milky Way Imaging Scroll Painting (MWISP) survey to analyze the cloud structure and the feedback effect from the W4 H ii region. Our observations showed that cold gas, traced by CO, mainly resided in the W3 GMC, with C18O concentrated in dense regions, while gas around W4 was dispersed. The 13CO position-position-velocity (PPV) distributions revealed a "C" shaped structure in the W3 cloud with more redshifted gas at higher galactic longitudes. A high density layer (HDL) region on the eastern side of the W3 region exhibited a flattened structure facing W4. Subdividing the area into sixteen subregions, we found that regions 6--9 on the HDL layer exhibited the strongest radiation, while clouds at the W4 bubble boundary not facing W3 exhibited weak signals, possibly due to star formation triggering and subsequent molecular gas dispersal by the H ii region. Analysis along four paths from the W4 H ii region to the far side showed a consistent trend of sharply increasing intensity followed by a slow decrease, indicating the gas was effectively eroded and heated by the photon dominated region (PDR) near the boundary of the H ii region. Clump identification based on 13CO emission revealed 288 structures categorized as "bubble," "HDL," and "quiescent" clumps. Analysis of mass-radius and Virial-mass relationships showed a potential for high-mass star formation in 29.5$&lt;!PCT!&gt;$ (85/288) of the clumps, with 39.2$&lt;!PCT!&gt;$ (113/288) being gravitationally bound. HDL clumps exhibited distinct $L/M$ and velocity dispersion, suggesting an earlier evolutionary stage and gravitational instability compared to quiescent and bubble clumps. Clump parameter differences provided evidence for triggered and dispersed effects of the W4 H ii region on the HDL and bubble regions, respectively.

Applying the Velocity Gradient Technique in NGC 1333: Comparison with Dust Polarization Observations

Magnetic fields (B-fields) are ubiquitous in the interstellar medium (ISM), and they play an essential role in the formation of molecular clouds and subsequent star formation. However, B-fields in interstellar environments remain challenging to measure, and their properties typically need to be inferred from dust polarization observations over multiple physical scales. In this work, we seek to use a recently proposed approach called the velocity gradient technique (VGT) to study B-fields in star-forming regions and compare the results with dust polarization observations in different wavelengths. The VGT is based on the anisotropic properties of eddies in magnetized turbulence to derive B-field properties in the ISM. We investigate that this technique is synergistic with dust polarimetry when applied to a turbulent diffused medium for the purpose of measuring its magnetization. Specifically, we use the VGT on molecular line data toward the NGC 1333 star-forming region (12CO, 13CO, C18O, and N2H+), and we compare the derived B-field properties with those inferred from 214 and 850 μm dust polarization observations of the region using Stratospheric Observatory for Infrared Astronomy/High-Resolution Airborne Wide-band Camera Plus and James Clerk Maxwell Telescope/POL-2, respectively. We estimate both the inclination angle and the 3D Alfvénic Mach number M A from the molecular line gradients. Crucially, testing this technique on gravitationally bound, dynamic, and turbulent regions, and comparing the results with those obtained from polarization observations at different wavelengths, such as the plane-of-sky field orientation, is an important test on the applicability of the VGT in various density regimes of the ISM. We in general do not find a close correlation between the velocity gradient inferred orientations and the dust inferred magnetic field orientations.

Deviations from the universal Initial Mass Function in binary star clusters

Abstract The stellar mass distribution in star-forming regions, stellar clusters and associations, the Initial Mass Function (IMF), appears to be invariant across different star-forming environments, and is consistent with the IMF observed in the Galactic field. Deviations from the field, or standard, IMF, if genuine, would be considered strong evidence for a different set of physics at play during the formation of stars in the birth region in question. We analyse N-body simulations of the evolution of spatially and kinematically substructured star-forming regions to identify the formation of binary star clusters, where two (sub)clusters which form from the same Giant Molecular Cloud orbit a common centre of mass. We then compare the mass distributions of stars in each of the subclusters and compare them to the standard IMF, which we use to draw the stellar masses in the star-forming region from which the binary cluster(s) form. In each binary cluster that forms, the mass distributions of stars in one subcluster deviates from the standard IMF, and drastically so when we apply similar mass resolution limits as for the observed binary clusters. Therefore, if a binary subcluster is observed to have an unusual IMF, this may simply be the result of dynamical evolution, rather than different physical conditions for star formation in these systems.

3D structure of the Milky Way out to 10 kpc from the Sun. Catalogue of large molecular clouds in the Galactic plane

3D structure of the Milky Way out to 10 kpc from the Sun. Catalogue of large molecular clouds in the Galactic plane

Molecular cloud matching in CO and dust in M33. II. Physical properties of giant molecular clouds

Understanding the physical properties such as mass, size, and surface mass density of giant molecular clouds or associations (GMCs/GMAs) in galaxies is crucial for gaining deeper insights into the molecular cloud and star formation (SF) processes. We determine these quantities for the Local Group flocculent spiral galaxy M33 using Herschel dust and archival $^ CO(2-1) $ data from the IRAM 30m telescope, and compare them to GMC/GMA properties of the Milky Way derived from CO literature data. For M33, we apply the Dendrogram algorithm on a novel 2D dust-derived Nhtwo map at an angular resolution of $18.2''$ and on the $^ CO(2-1) $ data and employ an factor map instead of a constant value. Dust and CO-derived values are similar, with mean radii of $ for the dust and $ for CO respectively. However, the largest GMAs have a radius of around $150\,$pc, similar to what was found in the Milky Way and other galaxies, suggesting a physical process that limits the size of GMAs. The less massive and smaller M33 galaxy also hosts less massive and lower-density GMCs compared to the Milky Way by an order of magnitude. Notably, the most massive ($&gt;$ a few $10^6\ M_ odot $) GMC population observed in the Milky Way is mainly missing in M33. The mean surface mass density of M33 is significantly smaller than that of the Milky Way and this is attributed to higher column densities of the largest GMCs in the Milky Way, despite similar GMC areas. We find no systematic gradients in physical properties with the galactocentric radius in M33. However, surface mass densities and masses are higher near the center, implying increased SF activity. In both galaxies, the central region contains $ of the total molecular mass. The index of the power-law spectrum of the GMC masses across the entire disk of M33 is $ and $ for dust- and CO-derived data, respectively. We conclude that GMC properties in M33 and the Milky Way are largely similar, though M33 lacks high-mass GMCs, for which there is no straightforward explanation. Additionally, GMC properties are only weakly dependent on the galactic environment, with stellar feedback playing a role that needs further investigation.

High-temperature 205Tl decay clarifies 205Pb dating in early Solar System

Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth1,2. Among such nuclei whose decay signatures are found in the oldest meteorites, 205Pb is a powerful example, as it is produced exclusively by slow neutron captures (the s process), with most being synthesized in asymptotic giant branch (AGB) stars3–5. However, making accurate abundance predictions for 205Pb has so far been impossible because the weak decay rates of 205Pb and 205Tl are very uncertain at stellar temperatures6,7. To constrain these decay rates, we measured for the first time the bound-state β− decay of fully ionized 205Tl81+, an exotic decay mode that only occurs in highly charged ions. The measured half-life is 4.7 times longer than the previous theoretical estimate8 and our 10% experimental uncertainty has eliminated the main nuclear-physics limitation. With new, experimentally backed decay rates, we used AGB stellar models to calculate 205Pb yields. Propagating those yields with basic galactic chemical evolution (GCE) and comparing with the 205Pb/204Pb ratio from meteorites9–11, we determined the isolation time of solar material inside its parent molecular cloud. We find positive isolation times that are consistent with the other s-process short-lived radioactive nuclei found in the early Solar System. Our results reaffirm the site of the Sun’s birth as a long-lived, giant molecular cloud and support the use of the 205Pb–205Tl decay system as a chronometer in the early Solar System.

Captured molecules could make a Bose star visible

A Bose star passing through cold molecular clouds may capture atoms, molecules, and dust particles. The observational signature of such an event would be a relatively small amount of matter that is gravitationally bound. This binding may actually be provided by invisible dark matter forming the Bose star. We may expect a relative excess of heavier atoms, molecules, and solid dust compared to the content of giant cold molecular clouds since the velocity of heavy particles at a given temperature is lower and it may be small compared to the escape velocity, vrms=3kBT/mgas≪vesc=2GM/R. Finally, the velocity of this captured matter cloud may correlate with the expected velocity of free dark matter particles (e.g., expected axion wind velocity relative to Earth). Published by the American Physical Society 2024

Extinction of Taurus, Orion, Perseus and California Molecular Clouds Based on the LAMOST, 2MASS, and Gaia Surveys. II. The Extinction Law

The extinction law from ultraviolet (UV) to infrared (IR; 0.2–24 μm) is determined by relying on the blue-edge method and color-excess ratios for some nearby molecular clouds, from the low-mass star-forming region to the massive star-forming region. The observational data are collected from nine photometric surveys, along with stellar parameters from the Apache Point Observatory Galaxy Evolution Experiment and LAMOST spectroscopic surveys. Within the uncertainties, the optical ratio of selective to total extinction ( RGBP ) does not vary substantially across the clouds, irrespective of the density, specifically RGBP=2.302±0.027 , where RGBP≡AGBP/EGBP,GRP . The IR extinction law is consistent with Wang & Chen. The extinction law in the UV band is compromised by the shallow depth with A V ≤ 2 mag and is hard to describe by one parameter R. In addition, the extinction in the WISE/W1 band is significantly larger than in the Spitzer/IRAC1 band in the dense regions, which is attributed to the ice water absorption.