Search

Fuelling star formation in large, discy galaxies requires a continuous supply of gas accreting into star-forming regions. Previously, we characterized this accretion in four Milky Way mass galaxies (⁠|$M_{\rm halo}\sim 10^{12}{\rm M}_{\odot }$|⁠) in the FIRE-2 cosmological zoom-in simulations. At |$z\sim 0$|⁠ , we found that gas within the inner circumgalactic medium (iCGM) approaches the disc with comparable angular momentum (AM) to the disc edge, joining in the outer half of the gaseous disc. Within the disc, gas moves inwards at velocities of |$\sim$| 1–5 km s |$^{-1}$| while fully rotationally supported. In this study, we analyse the torques that drive these flows. In all cases studied, we find that the torques in discs enable gas accreted near the disc edge to transport inwards and fuel star formation in the central few kpc. The primary sources of torque come from gravity, hydrodynamical forces, and the sub-grid |$P \mathrm{ d}V$| work done by supernova (SN) remnants interacting with gas on |$\lesssim$| 10 pc scales. These SNe remnant interactions induce negative torques within the inner disc and positive torques in the outer disc. The gas–gas gravitational, hydro, and 'feedback' torques transfer AM outwards to where accreting gas joins the disc, playing an important role in driving inflows and regulating disc structure. Gravitational torques from stars and dark matter provide an AM sink within the innermost regions of the disc and iCGM, respectively. Feedback torques are dominant within the disc, while gravitational and hydrodynamical torques have similar significance depending on the system/region. Torques from viscous shearing, magnetic forces, stellar winds, and radiative transfer are less significant. [ABSTRACT FROM AUTHOR]

This paper analyses spectropolarimetric observations of the classical T Tauri star (CTTS) GM Aurigae collected with SPIRou, the near-infrared spectropolarimeter at the Canada–France–Hawaii Telescope, as part of the SLS and SPICE Large Programs. We report for the first time results on the large-scale magnetic field at the surface of GM Aur using Zeeman Doppler imaging. Its large-scale magnetic field energy is almost entirely stored in an axisymmetric poloidal field, which places GM Aur close to other CTTSs with similar internal structures. A dipole of about 730 G dominates the large-scale field topology, while higher order harmonics account for less than 30 per cent of the total magnetic energy. Overall, we find that the main difference between our three reconstructed maps (corresponding to sequential epochs) comes from the evolving tilt of the magnetic dipole, likely generated by non-stationary dynamo processes operating in this largely convective star rotating with a period of about 6 d. Finally, we report a |$5.5\sigma$| detection of a signal in the activity-filtered radial velocity data of semi-amplitude |$110\pm 20$|  m s |$^{-1}$|  at a period of |$8.745\pm 0.009$|  d. If attributed to a close-in planet in the inner accretion disc of GM Aur, it would imply that this planet candidate has a minimum mass of |$1.10 \pm 0.30\, M_\mathrm{Jup}$| and orbits at a distance of |$0.082 \pm 0.002$|  au. [ABSTRACT FROM AUTHOR]

In this study we present 18 |$-$| 24 GHz and high-angular-resolution (0.5 arcsec) radio wavelength Australia Telescope Compact Array follow-up observations towards a sample of 39 HC H  ii region candidates. These objects, taken from a sample hosting 6.7 GHz methanol masers, were chosen due to the compact and optically thick nature of their continuum emission. We have detected 27 compact radio sources and constructed their spectral energy distributions over the 5–24 GHz range to determine the young H  ii region's physical properties, i.e. diameter, electron density |${\it n}_{\mbox{e}}$|⁠ , emission measure, Lyman continuum flux |${\it N}_{\mbox{Ly}}$|⁠ , and turnover frequency |${\nu }_{\mbox{t}}$|⁠. The flux measurements are fitted for 20 objects assuming an ionization-bounded H  ii region with uniform density model. For the remaining seven objects that lack constraints spanning both their optically thick and thin regimes, we utilize relations from the literature to determine their physical properties. Comparing these determined parameters with those of known hypercompact (HC) and ultracompact (UC) H  ii regions, we have identified 13 HC H  ii regions, six intermediate objects that fall between HC H  ii and UC H  ii regions, six UC H  ii regions and one radio jet candidate which increases the known population of HC H  ii regions by |$\sim$| 50 per cent. All the young and compact H  ii regions are embedded in dusty and dense clumps and |$\sim$| 80 per cent of the HC H  ii regions identified in this work are associated with various maser species (CH |$_3$| OH, H |$_2$| O, and OH). Four of our radio sources remain optically thick at 24 GHz; we consider these to be among the youngest HC H  ii regions. [ABSTRACT FROM AUTHOR]

We present deep, sub-arcsecond (⁠|$\sim$| 2000 au) resolution ALMA 0.82-mm observations of the former high-mass prestellar core candidate G11.92–0.61 MM2, recently shown to be an |$\sim$| 500 au-separation protobinary. Our observations show that G11.92–0.61 MM2, located in the G11.92–0.61 protocluster, lies on a filamentary structure traced by 0.82-mm continuum and N |$_2$| H |$^+$| (4-3) emission. The N |$_2$| H |$^+$| (4-3) spectra are multipeaked, indicative of multiple velocity components along the line of sight. To analyse the gas kinematics, we performed pixel-by-pixel Gaussian decomposition of the N |$_2$| H |$^+$| spectra using scousepy and hierarchical clustering of the extracted velocity components using acorns. Seventy velocity- and position-coherent clusters (called 'trees') are identified in the N |$_2$| H |$^+$| -emitting gas, with the eight largest trees accounting for |$\gt $| 60 per cent of the fitted velocity components. The primary tree, with |$\sim$| 20 per cent of the fitted velocity components, displays a roughly north–south velocity gradient along the filamentary structure traced by the 0.82-mm continuum. Analysing an |$\sim$| 0.17 pc-long substructure, we interpret its velocity gradient of |$\sim$| 10.5 km s |$^{-1}$|  pc |$^{-1}$| as tracing filamentary accretion towards MM2 and estimate a mass inflow rate of |$\sim 1.8\times 10^{-4}$| to 1.2 |$\times 10^{-3}$|  M |$_\odot$| yr |$^{-1}$|⁠. Based on the recent detection of a bipolar molecular outflow associated with MM2, accretion on to the protobinary is ongoing, likely fed by the larger scale filamentary accretion flows. If 50 per cent of the filamentary inflow reaches the protostars, each member of the protobinary would attain a mass of 8 M |$_\odot$| within |$\sim 1.6\times 10^5$| yr, comparable to the combined time-scale of the 70- μ m- and mid-infrared-weak phases derived for ATLASGAL-TOP100 massive clumps using chemical clocks. [ABSTRACT FROM AUTHOR]

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

NGC 6357, a star-forming complex at |$\sim 1.7$|  kpc from the Sun, contains giant molecular clouds and three prominent star clusters alongside H  ii regions, very massive stars and thousands of young stellar objects in different evolutionary stages. We present a combined infrared kinematic and time domain study of the line of sight towards this region enabled by the VVVX survey. In terms of kinematics, a novel discovery emerges an asymmetrical distribution in the vector point diagram. Some stars in the sample exhibit spatial proximity to dusty regions, with their proper motions aligned with filament projections, hinting at a younger population linked to triggered star formation. However, this distribution could also stem from an asymmetric stellar expansion event within NGC 6357, warranting further investigation. Comparing these data with Gaia revealed inconsistencies likely due to high-extinction levels in the region. Additionally, owing to accretion episodes and surface cool spots, young stars display high variability. Using the |$K_{\rm s}$| -band time series data, we overcome the extreme levels of extinction towards the region, and compile a catalogue of 774 infrared light curves of young stars. Each light curve has been characterized in terms of asymmetry and periodicity, to infer the dominant underlying physical mechanism. These findings are then correlated with evolutionary stages, aiming to uncover potential age disparities among the observed stars. This study contributes to our understanding the intricate dynamics and evolutionary processes within NGC 6357, offering valuable insights into the formation and development of stellar populations within such complex environments. [ABSTRACT FROM AUTHOR]

We present the initial data for the |$(J = 3 \rightarrow 2)$| transition of |$^{13}\text{CO}$| obtained from the central molecular zone (CMZ) of the Milky Way as part of the CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). Covering |$359^{\circ } \le l \le 1^{\circ }$| and |$|b| \le 0.5^{\circ }$| with an angular resolution of 19 arcsec, velocity resolution of 1 km s |$^{-1}$|⁠ , and rms |$\Delta {T_{\rm A}^{*}} = 0.59\, \mathrm{K}$| at these resolutions, our observations unveil the complex structure of the CMZ molecular gas in improved detail. Complemented by the |$\rm {^{12}CO}$| CHIMPS2 data, we estimate a median optical depth of |$\tau _{13} = 0.087$|⁠. The preliminary analysis yields a median |$^{13}\text{CO}$| column-density range equal to |$N(^{13}{\rm CO}) = 2{\!-\!}5 \times 10^{18}\, \mathrm{cm}^{-2}$|⁠ , median H |$_{2}$| column density equal to |$N(\mathrm{H_{2}}) = 4 \times 10^{22}\, \mathrm{cm}^{-2}$| to |$1 \times 10^{23}\, \mathrm{cm}^{-2}$|⁠. We derive |$N({\rm H_{2}})$| -based total mass estimates of |$M({\rm H}_{2}) = 2{\!-\!}6 \times 10^{7}\, \mathrm{M}_{\odot }$|⁠ , in agreement with previous studies. We analyse the relationship between the integrated intensity of |$^{13}\text{CO}$| and the surface density of compact sources identified by Herschel Hi-GAL, and find that younger Hi-GAL sources detected at 500  |$\rm{\mu m}$| but not at 70  |$\rm{\mu m}$| follow the dense gas of the CMZ more closely than those that are bright at 70  |$\rm{\mu m}$|⁠. The latter, actively star-forming sources appear to be more associated with material in the foreground spiral arms. [ABSTRACT FROM AUTHOR]

We present the first large-scale 3D kinematic study of |$\sim$| 2700 spectroscopically confirmed young stars (⁠|$\lt $| 20 Myr) in 18 star clusters and OB associations (hereafter groups) from the combination of Gaia astrometry and Gaia –ESO Survey spectroscopy. We measure 3D velocity dispersions for all groups, which range from 0.61 to 7.4 km s |$^{-1}$| (1D velocity dispersions of 0.35–4.3 km s |$^{-1}$| ). We find the majority of groups have anisotropic velocity dispersions, suggesting they are not dynamically relaxed. From the 3D velocity dispersions, measured radii, and estimates of total mass, we estimate the virial state and find that all systems are super-virial when only the stellar mass is considered, but that some systems are sub-virial when the mass of the molecular cloud is taken into account. We observe an approximately linear correlation between the 3D velocity dispersion and the group mass, which would imply that the virial state of groups scales as the square root of the group mass. However, we do not observe a strong correlation between virial state and group mass. In agreement with their virial state, we find that nearly all of the groups studied are in the process of expanding and that the expansion is anisotropic, implying that groups were not spherical prior to expansion. One group, Rho Oph, is found to be contracting and in a sub-virial state (when the mass of the surrounding molecular cloud is considered). This work provides a glimpse of the potential of the combination of Gaia and data from the next generation of spectroscopic surveys. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) bubble structure of the Sgr-B molecular-cloud complex is derived by a kinematical analysis of CO-line archival cube data of the Galactic Centre (GC) observed with the Nobeyama 45-m telescope. The line-of-sight depth is estimated by applying the face-on transformation method of radial velocity to the projected distance on the Galactic plane considering the Galactic rotation of the central molecular zone (CMZ). The 3D complex exhibits a conical-horn structure with the Sgr-B2 cloud located in the farthest end on the line of sight at radial velocity |$v_{\rm lsr} \sim 70$|  km s |$^{-1}$|⁠ , and the entire complex composes a lopsided bubble opening toward the Sun at |$v_{\rm lsr}\sim 50$| to 30 km s |$^{-1}$|⁠. The line-of-sight extent of the complex is |$\sim 100$|  pc according to the large velocity extent for several tens of km s |$^{-1}$| from Sgr-B2 to the outskirts. The entire complex exhibits a flattened conical bubble with full sizes |$\sim 40 \ {\rm pc} \times 20 \ {\rm pc} \times 100 \ {\rm pc}$| in the l, b and line-of-sight directions, respectively. Based on the 3D analysis, we propose a formation scenario of the giant molecular bubble structure due to a galactic bow shock, and suggest that the star formation in Sgr-B2 was enhanced by dual-side compression (DSC) of the B2 cloud by the Galactic shock wave from up-stream and expanding H  ii region from the down-stream side of the GC Arm I in Galactic rotation. [ABSTRACT FROM AUTHOR]

We present a catalogue of dense cores and filaments in a |$3.8^\circ \times 2.4^\circ$| field around the TMC1 region of the Taurus molecular cloud. The catalogue was created using photometric data from the Herschel SPIRE and PACS instruments in the 70, 160, 250, 350, and 500 μ m continuum bands. Extended structure in the region was reconstructed from a Herschel column density map. Power spectra and probability density functions (PDFs) of this structure are presented. The PDF splits into lognormal and power-law forms, with the high-density power-law component associated primarily with the central part of TMC1. The total mass in the mapped region is 2000 M |$_\odot$|⁠ , of which 34 per cent is above an extinction of |$A_V\sim 3$| mag – a level that appears as a break in the PDF and as the minimum column density at which dense cores are found. A total of 35 dense filaments were extracted from the column density map. These have a typical full width at half-maximum (FWHM) width of 0.07 pc, but the TMC1 filament itself has a mean FWHM of |$\sim 0.13$| pc. The thermally supercritical filaments in the region are aligned orthogonal to the prevailing magnetic field direction. Derived properties for the supercritical TMC1 filament support the scenario of it being relatively young. A catalogue of 44 robust and candidate prestellar cores is created and is assessed to be complete down to 0.1 M |$_\odot$|⁠. The combined prestellar core mass function for the TMC1 and L1495 regions is well fit by a single lognormal distribution and is comparable to the standard initial mass function. [ABSTRACT FROM AUTHOR]

The majority of stars are in binary/multiple systems. How such systems form in turbulent, magnetized cores of molecular clouds in the presence of non-ideal magnetohydrodynamic (MHD) effects remains relatively underexplored. Through athena ++-based non-ideal MHD adaptive mesh refinement simulations with ambipolar diffusion, we show that the collapsing protostellar envelope is dominated by dense gravo-magneto-sheetlets, a turbulence-warped version of the classic pseudodisc produced by anisotropic magnetic resistance to the gravitational collapse, in agreement with previous simulations of turbulent, magnetized single-star formation. The sheetlets feed mass, magnetic fields, and angular momentum to a Dense ROtation-Dominated (DROD) structure, which fragments into binary/multiple systems. This DROD fragmentation scenario is a more dynamic variant of the traditional disc fragmentation scenario for binary/multiple formation, with dense spiral filaments created by inhomogeneous feeding from the highly structured larger-scale sheetlets rather than the need for angular momentum transport, which is dominated by magnetic braking. Provided that the local material is sufficiently demagnetized, with a plasma- |$\beta$| of 10 or more, collisions between the dense spiralling filaments play a key role in facilitating gravitational collapse and stellar companion formation by pushing the local magnetic Toomre parameter |$Q_\mathrm{m}$| below unity. This mechanism can naturally produce in situ misaligned systems on the 100-au scale, often detected with high-resolution Atacama Large Millimeter Array (ALMA) observations. Our simulations also highlight the importance of non-ideal MHD effects, which affect whether fragmentation occurs and, if so, the masses and orbital parameters of the stellar companions formed. [ABSTRACT FROM AUTHOR]

We study the wide-binary eccentricity (e) distribution in young star clusters and the role of turbulence in setting the form of the e distribution using magnetohydrodynamical simulations of star cluster formation. The simulations incorporate gravity, turbulence, magnetic fields, protostellar heating, and jets/outflows. We find that (1) simulations that employ purely compressive turbulence driving produce binaries with a superthermal e distribution [ |$\alpha \gt 1$| in |$p(e) \propto e^\alpha$| ], while simulations with purely solenoidal driving or natural mixture of driving modes produce subthermal/thermal distributions (⁠|$\alpha \le$| 1), (2) the e distribution over the full range of binary separations in our simulations is set at the early stages of the star cluster formation process, (3) while binaries (separation of |$r_{\mathrm{pair}} \le 1000\, \mathrm{AU}$|⁠) have subthermal to thermal e distributions (⁠|$\alpha \sim 0.8$|⁠), wide binaries (⁠|$r_{\mathrm{pair}} \gt 1000\, \mathrm{AU}$|⁠) have a superthermal distribution (⁠|$\alpha \sim 1.8$|⁠), and (4) low-mass binary systems (system masses of |$M_{\mathrm{sys}} \le 0.8\, \mathrm{M_\odot }$|⁠) have a highly superthermal distribution (⁠|$\alpha \sim 2.4$|⁠), whereas high-mass systems (⁠|$M_{\mathrm{sys}} \gt 0.8\, \mathrm{M_\odot }$|⁠) exhibit a subthermal/thermal distribution (⁠|$\alpha \sim 0.8$|⁠). The binary eccentricity distribution is often modelled as a thermal distribution. However, our results suggest that the e distribution depends on the range of separation of the sampled binaries, which agrees with the findings from recent Gaia observations. We conclude that the dependence of the e distribution on the binary separation and mass is linked to the binary formation mechanism governed by the turbulent properties of the parent cloud. [ABSTRACT FROM AUTHOR]

We present the overview and first results from the North-PHASE Legacy Survey, which follows six young clusters for five years, using the 2 deg |$^2$| FoV of the JAST80 telescope from the Javalambre Observatory (Spain). North-PHASE investigates stellar variability on time-scales from days to years for thousands of young stars distributed over entire clusters. This allows us to find new YSO, characterize accretion, and study inner disc evolution within the cluster context. Each region (Tr 37, Cep OB3, IC 5070, IC 348, NGC 2264, and NGC 1333) is observed in six filters (SDSS griz, u band, and J0660, which covers H |$\alpha$|⁠), detecting cluster members as well as field variable stars. Tr 37 is used to prove feasibility and optimize the variability analysis techniques. In Tr 37, variability reveals 50 new YSO, most of them proper motion outliers. North-PHASE independently confirms the youth of astrometric members, efficiently distinguishes accreting and non-accreting stars, reveals the extent of the cluster populations along Tr37/IC 1396 bright rims, and detects variability resulting from rotation, dips, and irregular bursts. The proper motion outliers unveil a more complex star formation history than inferred from Gaia alone, and variability highlights previously hidden proper motion deviations in the surrounding clouds. We also find that non-YSO variables identified by North-PHASE cover a different variability parameter space and include long-period variables, eclipsing binaries, RR Lyr, and |$\delta$| Scuti stars. These early results also emphasize the power of variability to complete the picture of star formation where it is missed by astrometry. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive multiwavelength investigation of the intermediate-age open cluster NGC 1912. We identified 401 member stars for NGC 1912 using K-nearest neighbour and Gaussian Mixture Model machine learning techniques. The fundamental parameters determined for the cluster are metallicity (z) = 0.0141 |$\pm$| 0.0006, log(age) = 8.519 |$\pm$| 0.040, binary fraction (⁠|$b_{\text{frac}}$|⁠) = 0.445 |$\pm$| 0.035, visual extinction (⁠|$A_V$|⁠) = 0.864 |$\pm$| 0.033 mag, total-to-selective extinction ratio (⁠|$R_V$|⁠) = 3.007 |$\pm$| 0.096, distance = 1096 |$\pm$| 15 pc. The central density (⁠|$\rho _o$|⁠), core radius (⁠|$r_c$|⁠), tidal radius (⁠|$r_t$|⁠), and background density (⁠|$\rho _{\mathrm{bg}}$|⁠) for the cluster are obtained as 0.643 |$\pm$| 0.067 stars arcmin |$^{-2}$| , 7.743 |$\pm$| 0.784 arcmin, 84.633 |$\pm$| 7.188 arcmin, and 0.001 |$\pm$| 0.000 stars arcmin |$^{-2}$| , respectively. Dynamical mass segregation study revealed a concentration of some apparently massive stars towards the cluster centre. Polarimetric analysis of 90 stars in |$BVR_cI_c$| wavelength bands revealed that the observed polarization in NGC 1912 is not solely attributed to interstellar dust. The Galactic magnetic field is dominant in this region. Dust grain sizes within the intracluster region are found to be relatively smaller than that of the general ISM. The extinction map revealed the existence of a potential 'interstellar bubble' located close to the cluster region. Towards the periphery of the probable bubble region, which displays an ovoid-like geometry, 16 probable young stellar objects have been detected, suggesting the ongoing triggering of secondary star formation events in this region. [ABSTRACT FROM AUTHOR]

First stars play crucial roles in the development of the Universe, influencing events like cosmic reionization and the chemcal enrichment of the intergalactic medium. While first stars are conventionally thought to form at around |$z \sim 20$| –30 in the standard |$\Lambda$| cold dark matter (⁠|$\Lambda$| CDM) cosmology, observational constraints on small-scale (⁠|$\\lt $| Mpc) density fluctuations remain limited, possibly differing significantly from the scale-invariant fluctuations assumed in the |$\Lambda $| CDM model. Should this be the case, the formation of first stars could occur much earlier than typically predicted. In this study, we investigate the formation process of first stars in the extremely early epochs of |$z \gtrsim 100$| in the post-recombination Universe. At such early times, the effects of the warm cosmic microwave background (CMB) become significant. We calculate the collapse of primordial star-forming clouds using a one-zone thermo-chemical model that accounts for CMB influences on radiative heating, Compton cooling, and photodissociation reactions. We found that the impact of the CMB on the evolution is limited at |$z \lesssim 100 $|⁠ , with the temperature evolution closely resembling the conventional model. However, within the range |$100 \lesssim z \lesssim 400$|⁠ , the formation of H |$_{2}$| via the H |$^{-}$| channel is impeded by H |$^{-}$| photo-detachment induced by the CMB, leading to higher temperatures compared to standard thermal evolution. Consequently, first stars with masses exceeding |$1000\, {M}_{\odot }$| can emerge at |$z \gtrsim 100$|⁠. Furthermore, at |$z \gtrsim 500$|⁠ , the temperature evolution becomes nearly isothermal at several thousand Kelvin solely due to atomic cooling, as H |$_{2}$| formation is entirely suppressed, including the less-efficient H |$_2^{+}$| channel, which is blocked by H |$_2^{+}$| photodissociation. In such cases, supermassive stars with masses around |$\sim 10^{5}\, {M}_{\odot }$| are expected to form solely via atomic cooling. These findings emphasize the significant variation in the typical mass of the first stars depending on the epoch of formation. [ABSTRACT FROM AUTHOR]

Recent cosmological hydrodynamic simulations have suggested that the first stars in the Universe often form as binary or multiple systems. However, previous studies typically overlooked the potential influence of magnetic fields during this process, assuming them to be weak and minimally impactful. Emerging theoretical investigations, however, propose an alternative perspective, suggesting that turbulent dynamo effects within first-star forming clouds can generate strong magnetic fields. In this study, we perform three-dimensional ideal magnetohydrodynamics simulations, starting from the gravitational collapse of a turbulent cloud core to the early accretion phase, where disk fragmentation frequently occurs. Our findings reveal that turbulent magnetic fields, if they reach an equipartition level with turbulence energy across all scales during the collapse phase, can significantly affect the properties of the multiple systems. Specifically, both magnetic pressure and torques contribute to disk stabilization, leading to a reduction in the number of fragments, particularly for low-mass stars. Additionally, our observations indicate the launching of protostellar jets driven by magnetic pressure of toroidal fields, although their overall impact on star formation dynamics appears to be minor. Given the case with which seed magnetic fields amplify to the full equipartition level, our results suggest that magnetic fields likely play a significant role in shaping the initial mass function of the first stars, highlighting the importance of magnetic effects on star formation in the early Universe. [ABSTRACT FROM AUTHOR]

In our previous study (Tsukamoto et al. 2023b, PASJ, 75, 835), we investigated the formation and early evolution of protoplanetary disks with 3D non-ideal magnetohydrodynamics simulations considering dust growth, and found that the modified equations of the conventional steady accretion disk model that consider magnetic braking, dust growth, and ambipolar diffusion reproduce the disk structure (such as density and vertical magnetic field) obtained from simulations very well. In this paper, as a sequel to our previous study, we analytically investigate the structure and evolution of protoplanetary disks corresponding to Class 0/I young stellar objects using the modified steady accretion disk model combining an analytical model of envelope accretion. We estimate that the disk radius is several astronomical units at the disk formation epoch and increases to several hundred astronomical units at the end of the accretion phase. The disk mass is estimated to be |$0.01 \lesssim M_{\rm disk} \lesssim 0.1 \, M_\odot$| for a disk with a radius of several tens of astronomical units and a mass accretion rate of |$\dot{M}_{\rm disk} \sim 10^{-6} \, M_\odot \,\, {\rm yr^{-1}}$|⁠. These estimates seems to be consistent with recent observations. We also found that, with typical disk ionization rates (ζ ≳ 10−19 s−1) and a moderate mass accretion rate (⁠|$\dot{M}_{\rm disk}\gtrsim 10^{-8} \, M_\odot \,\, {\rm yr^{-1}}$|⁠), magnetorotational instability is suppressed in the disk because of low plasma β and efficient ambipolar diffusion. We argue that the radial profile of specific angular momentum (or rotational velocity) at the disk outer edge should be continuously connected to that of the envelope if the disk evolves by magnetic braking, and should be discontinuous if the disk evolves by an internal angular momentum transport process such as gravitational instability or magnetorotational instability. Future detailed observations of the specific angular momentum profile around the disk outer edge are important for understanding the angular momentum transport mechanism of protoplanetary disks. [ABSTRACT FROM AUTHOR]

In order to develop a complete theory of star formation, one essentially needs to know two things: what collapses and how long it takes. This is the second paper in a series, where we query how long a parcel of gas takes to collapse and the process it undergoes. We embed pseudo-Lagrangian tracer particles in simulations of collapsing molecular clouds, identify the particles that end in dense knots, and then examine the collapse history of the gas. We find a nearly universal behaviour of cruise-then-collapse, wherein a core stays at intermediate densities for a significant fraction of its life before finally collapsing. We identify time immediately before each core collapses, |$t_{\rm {sing}}$|⁠ , and examine how it transitions to high density. We find that the time to collapse is uniformly distributed between |$0.25 t_{\rm {ff}}$| and the end of the simulation at |$\sim\!\! 1 t_{\rm {ff}}$|⁠ , and that the duration of collapse is universally short, |$\Delta t \sim 0.1 t_{\rm {ff}}$|⁠ , where |$t_{\rm {ff}}$| is the free-fall time at the mean density. We describe the collapse in three stages: collection, hardening, and singularity. Collection sweeps low-density gas into moderate density. Hardening brings kinetic and gravitational energies into quasi-equipartition. Singularity is the free-fall collapse, forming an envelope in rough energy balance and central overdensity in |$\sim\!\! 0.1 t_{\rm {ff}}$|⁠. [ABSTRACT FROM AUTHOR]

Context. Interstellar surface chemistry is a complex process that occurs in icy layers that have accumulated onto grains of different sizes. The efficiency of the surface processes often depends on the immediate environment of the adsorbed molecules. Aims. We investigated how gas-grain chemistry changes when the surface molecule binding energy is modified, depending on the properties of the surface. Methods. In a gas-grain astrochemical model, molecular binding energy gradually changes for three different environments –(1) the bare grain surface, (2) polar water-dominated ices, and (3) weakly polar carbon monoxide-dominated ices. In addition to diffusion, evaporation, and chemical desorption, photodesorption was also made binding energy-dependent, in line with experimental results. These phenomena occur in a collapsing prestellar core model that considers five grain sizes with ices arranged into four layers. Results. Variable desorption energy moderately affects gas-grain chemistry. Bare-grain effects slow down ice accumulation, while easier diffusion of molecules on weakly polar ices promotes the production of carbon dioxide. Efficient chemical desorption from bare grains significantly delays the appearance of the first ice monolayer. Conclusions. The combination of multiple aspects of grain surface chemistry creates a gas-ice balance that is different from simpler models. The composition of the interstellar ices is regulated by several binding-energy dependent desorption mechanisms. Their actions overlap in time and space, explaining the similar proportions of major ice components (water and carbon oxides) observed in all directions. [ABSTRACT FROM AUTHOR]

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

Context. Signposts of early planet formation are ubiquitous in substructured young discs. Dense, hot, and high-pressure regions that formed during the gravitational collapse process, integral to star formation, facilitate dynamical mixing of dust within the protostellar disc. This provides an incentive to constrain the role of gas and dust interaction and resolve potential zones of dust concentration during star and disc formation stages. Aims. We explore whether the thermal and dynamical conditions that developed during protostellar disc formation can generate gas flows that efficiently mix and transport the well-coupled gas and dust components. Methods. We simulated the collapse of dusty molecular cloud cores with the hydrodynamics code PLUTO augmented with radiation transport and self-gravity. We used a two-dimensional axisymmetric geometry and followed the azimuthal component of the velocity. The dust was treated as Lagrangian particles that are subject to drag from the gas, whose motion is computed on a Eulerian grid. We considered 1, 10, and 100 µm-sized neutral, spherical dust grains. Importantly, the equation of state accurately includes molecular hydrogen dissociation. We focus on molecular cloud core masses of 1 and 3 M⊙ and explore the effects of different initial rotation rates and cloud core sizes. Results. Our study underlines mechanisms for the early transport of dust from the inner hot disc regions via the occurrence of two transient gas motions, namely meridional flow and outflow. The vortical flow fosters dynamical mixing and retention of dust, while the thermal pressure driven outflow replenishes dust in the outer disc. Notably, these phenomena occur regardless of the initial cloud core mass, size, and rotation rate. Conclusions. Young dynamical precursors to planet-forming discs exhibit regions with complex hydrodynamical gas features and high-temperature structures. These can play a crucial role in concentrating dust for subsequent growth into protoplanets. Dust transport, especially, from sub-au scales surrounding the protostar to the outer relatively cooler parts, offers an efficient pathway for thermal reprocessing during pre-stellar core collapse. [ABSTRACT FROM AUTHOR]

Context. The detections of narrow channels of accretion toward protostellar disks, known as streamers, have increased in number in the last few years. However, it is unclear whether streamers are a common feature around protostars that were previously missed, or if they are a rare phenomenon. Aims. Our goals are to obtain the incidence of streamers toward a region of clustered star formation and to trace the origins of their gas to determine whether they originate within the filamentary structure of molecular clouds or from beyond. Methods. We used combined observations of the nearby NGC 1333 star-forming region, carried out with the NOEMA interferometer and the IRAM 30m single dish. Our observations cover the area between the systems IRAS 4 and SVS 13. We traced the chemically fresh gas within NGC 1333 with HC3N molecular gas emission and the structure of the fibers in this region with N2H+ emission. We fit multiple velocity components in both maps and used clustering algorithms to recover velocity-coherent structures. Results. We find streamer candidates toward 7 out of 16 young stellar objects within our field of view. This represents an incidence of approximately 40% of young stellar objects with streamer candidates in a clustered star-forming region. The incidence increases to about 60% when we only considered embedded protostars. All streamers are found in HC3N emission. Conclusions. Given the different velocities between HC3N and N2H+ emission, and because by construction, N2H+ traces the fiber structure, we suggest that the gas that forms the streamers comes from outside the fibers. This implies that streamers can connect cloud material that falls onto the filaments with protostellar disk scales. [ABSTRACT FROM AUTHOR]

Context. The presence of grains is key to the synthesis of molecules in the interstellar medium that cannot form in the gas phase due to its low density and temperature conditions. In these reactions, the role of the grains is to enhance the encounter rate of the reactive species on their surfaces and to dissipate the energy excess of largely exothermic reactions, but less is known about their role as chemical catalysts; namely, bodies that provide low activation energy pathways with enhanced reaction rates. Different refractory materials with catalytic properties, such as those containing space-abundant d-block transition metals like iron (Fe), are present in astrophysical environments. Aims. Here, we report for first time mechanistic insights into the Fischer-Tropsch-type (FTT) synthesis of ethanol (CH3CH2OH), through ketene (CH2CO) and acetaldehyde (CH3CHO) intermediates, and methane (CH4) via a chain growing mechanism using a single-Fe atom supported on silica (SiO2) surfaces as a heterogeneous astrocatalyst. Methods. Quantum chemical simulations based on extended periodic surfaces were carried out to characterize the potential energy surfaces of the FTT chain growing mechanism. Calculations of the binding energies of reaction intermediates and products and Rice–Ramsperger–Kassel–Marcus kinetic calculations were performed to evaluate catalytic efficiencies and determine the feasibility of the reactions in different astrophysical environments. Results. Mechanistic studies demonstrate that the FTT chain growing mechanism enters into direct competition with FTT methanol formation, since formation of the CH2 chain growth initiator is feasible. The coupling of the CH2 with CO (forming ketene) and subsequent H2 additions yield acetaldehyde and finally ethanol, while direct H2 addition to CH2 produces methane. Thermodynamically, both processes are largely exergonic, but they present energy barriers that require external energy inputs to be overcome. Kinetic calculations demonstrate the strong temperature dependency of the FTT processes as tunneling does not dominate. Conclusions. The results could explain the presence of CH3CH2OH and CH4 in diverse astrophysical regions where current models fail to reproduce their observational quantities. The evidence that the chain growing mechanism is operating opens a new reactivity paradigm toward the formation of complex organic molecules, which is constrained by the temperature-dependent behaviour of the FTT reactions and by making their energy features a crucial aspect. [ABSTRACT FROM AUTHOR]

The kinetic temperature structure of the massive filament DR21 within the Cygnus X molecular cloud complex has been mapped using the IRAM 30 m telescope. This mapping employed the para-H2CO triplet (JKaKc = 303−202, 322−221, and 321–220) on a scale of ~0.1 pc. By modeling the averaged line ratios of para-H2CO 322–221/303–202 and 321–220/303 –202 with RADEX under non local thermodynamic equilibrium (LTE) assumptions, the kinetic temperature of the dense gas was derived, which ranges from 24 to 114 K, with an average temperature of 48.3 ± 0.5 K at a density of n(H2)= 105 cm−3. In comparison to temperature measurements using NH3 (1, 1)/(2,2) and far-infrared (FIR) wavelengths, the para-H2CO(3–2) lines reveal significantly higher temperatures. The dense clumps in various regions appear to correlate with the notable kinetic temperature (Tkin ≳ 50 K) of the dense gas traced by H2CO. Conversely, the outskirts of the DR21 filament display lower temperature distributions (Tkin < 50 K). Among the four dense cores (N44, N46, N48, and N54), temperature gradients are observed on a scale of ~0.1–0.3 pc. This suggests that the warm dense gas traced by H2CO is influenced by internal star formation activity. With the exception of the dense core N54, the temperature profiles of these cores were fitted with power-law indices ranging from −0.3 to −0.5, with a mean value of approximately −0.4. This indicates that the warm dense gas probed by H2CO is heated by radiation emitted from internally embedded protostar(s) and/or clusters. While there is no direct evidence supporting the idea that the dense gas is heated by shocks resulting from a past explosive event in the DR21 region on a scale of ~0.1 pc, our measurements of H2CO toward the DR21W1 region provide compelling evidence that the dense gas in this specific area is indeed heated by shocks originating from the western DR21 flow. Higher temperatures as traced by H2CO appear to be associated with turbulence on a scale of ~0.1 pc. The physical parameters of the dense gas as determined from H2CO lines in the DR21 filament exhibit aremarkable similarity to the results obtained in OMC-1 and N113, albeit on a scale of approximately 0.1–0.4 pc. This may imply that the physical mechanisms governing the dynamics and thermodynamics of dense gas traced by H2CO in diverse star formation regions may be dominated by common underlying principles despite variations in specific environmental conditions. [ABSTRACT FROM AUTHOR]

Context. Understanding circumstellar disks is of prime importance in astrophysics; however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. Aims. We aim to elucidate the small-scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. Methods. We carried out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent, dense molecular cloud core to stellar densities. We studied the birth of the protostar, the circumstellar disk, and its early evolution (< 6 yr after protostellar formation). Results. Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot (∼103 K), dense, and highly flared circumstellar disk. The protostar is embedded within the disk such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock was shown to be supercritical, whereas its equatorial counterpart is subcritical. We also find a remarkable convergence of our results with respect to initial conditions. Conclusions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger-scale physics. [ABSTRACT FROM AUTHOR]

Aims. We aim to identify and characterize cores in the high-mass protocluster W49A, determine their evolutionary stages, and measure the associated lifetimes. Methods. We built a catalog of 129 cores extracted from an ALMA 1.3 mm continuum image at 0.26″ (2900 au) angular resolution. The association between cores and hypercompact or ultracompact HII (H/UC HII) regions was established from the analysis of VLA 3.3 cm continuum and H30α line observations. We also looked for emission of hot molecular cores (HMCs) using the methyl formate doublet at 218.29 GHz. Results. We identified 40 cores associated with an H/UC HII region and 19 HMCs over the ALMA mosaic. The 52 cores with an H/UC HII region and/or an HMC are assumed to be high-mass protostellar cores, while the rest of the core population likely consists of prestellar cores and low-mass protostellar cores. We found a good agreement between the two tracers of ionized gas, with 23 common detections and only four cores detected at 3.3 cm and not in H30α. The spectral indexes from 3.3 cm to 1.3 mm range from 1, for the youngest cores with partially optically thick free-free emission, to about −0.1, which is for the optically thin free-free emission obtained for cores that are likely more evolved. Conclusions. Using the H/UC HII regions as a reference, we found the statistical lifetimes of the HMC and massive protostellar phases in W49N to be about 6 × 104 yr and 1.4 × 105 yr, respectively. We also showed that HMCs can coexist with H/UC HII regions during a short fraction of the core lifetime, about 2 × 104 yr. This indicates a rapid dispersal of the inner molecule envelope once the HC HII is formed. [ABSTRACT FROM AUTHOR]

Aims. We study a new mechanism of dust accumulation and planetesimal formation in a gravitationally unstable disk with suppressed magnetorotational instability and we compare it with the classical dead zone in a layered disk model. Methods. We used numerical hydrodynamics simulations in the thin-disk limit (FEOSAD code) to model the formation and long-term evolution of gravitationally unstable disks, including dust dynamics and growth. Results. We found that in gravitationally unstable disks with a radially varying strength of gravitational instability (GI), an inner region (of several astronomical units) of low mass and angular momentum transport is formed. This region is characterized by a low effective value for the αGI parameter, often used to describe the efficiency of mass transport by GI in young protoplanetary disks. The inner region is also similar in terms of characteristics to the dead zone in the layered disk model. As the disk forms and evolves, the GI-induced dead zone accumulates a massive dust ring, which is susceptible to the development of the streaming instability. The model and observationally inferred dust masses and radii may differ significantly in gravitationally unstable disks with massive inner dust rings. Conclusions. The early occurrence of the GI-induced dust ring, followed by the development of the streaming instability suggest that this mechanism may be behind the formation of the first generation of planetesimals in the inner terrestrial zone of the disk. The proposed mechanism, however, crucially depends on the susceptibility of the disk to gravitational instability and requires the magnetorotational instability to be suppressed. [ABSTRACT FROM AUTHOR]

Context. 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. Aims. 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. Methods. 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″ 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. Results. 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″ beam. [ABSTRACT FROM AUTHOR]

In the Orion Nebula Cluster (ONC), protoplanetary disks exhibit ionized gas clouds in the form of a striking teardrop shape as massive stars irradiate the disk material. We present the first spatially and spectrally resolved observations of 12 such objects, known as proplyds, using integral field spectroscopy observations performed with the Multi-Unit Spectroscopic Explorer (MUSE) instrument in Narrow Field Mode (NFM) on the Very Large Telescope (VLT). We present the morphology of the proplyds in seven emission lines and measure the radius of the ionization front (I-front) of the targets in four tracers, covering transitions of different ionization states for the same element. We also derive stellar masses for the targets. The measurements follow a consistent trend of increasing I-front radius for a decreasing strength of the far-UV radiation as expected from photoevaporation models. By analyzing the ratios of the I-front radii as measured in the emission lines of Hα, [O I] 6300 A, [O II] 7330 A, and [O III] 5007 A, we observe the ionization stratification, that is, the most ionized part of the flow being the furthest from the disk (and closest to the UV source). The ratios of ionization front radii scale in the same way for all proplyds in our sample regardless of the incident radiation. We show that the stratification can help constrain the densities near the I-front by using a 1D photoionization model. We derive the upper limits of photoevaporative mass-loss rates (Ṁloss) by assuming ionization equilibrium, and estimate values in the range 1.07–94.5 × 10−7M⊙ yr−1, with Ṁloss values decreasing towards lower impinging radiation. We do not find a correlation between the mass-loss rate and stellar mass. The highest mass-loss rate is for the giant proplyd 244–440. These values of Ṁloss, combined with recent estimates of the disk mass with ALMA, confirm previous estimates of the short lifetime of these proplyds. This work demonstrates the potential of this MUSE dataset and offers a new set of observables to be used to test current and future models of external photoevaporation. [ABSTRACT FROM AUTHOR]

Context. Regularly spaced star-forming regions along the spiral arms of nearby galaxies provide insight into the early stages and initial conditions of star formation. The regular separation of these star-forming regions suggests spiral arm instability as their origin. Aims. We explore the effects of magnetic fields on the spiral arm instability. Methods. We use 3D global magnetohydrodynamical simulations of isolated spiral galaxies, comparing three different initial plasma β values (ratios of the thermal to magnetic pressure) of β = ∞, 50, and 10. We perform a Fourier analysis to calculate the separation of the over-dense regions that formed as a result of the spiral instability. We then compare the separations with observations. Results. We find that the spiral arms in the hydro case (β = ∞) are unstable. The fragments are initially connected by gas streams that are reminiscent of the Kelvin-Helmholtz instability. For β = 50, the spiral arms also fragment, but the fragments separate earlier and tend to be slightly elongated in the direction perpendicular to the spiral arms. However, in the β = 10 run, the arms are stabilised against fragmentation by magnetic pressure. Despite the difference in the initial magnetic field strengths of the β = 50 and 10 runs, the magnetic field is amplified to βarm ∼ 1 inside the spiral arms for both runs. The spiral arms in the unstable cases (hydro and β = 50) fragment into regularly spaced over-dense regions. We determine their separation to be ∼0.5 kpc in the hydro and ∼0.65 kpc in the β = 50 case. These two values agree with the observed values found in nearby galaxies. We find a smaller median characteristic wavelength of the over-densities along the spiral arms of 0.73−0.36+0.31 kpc in the hydro case compared to 0.98−0.46+0.49 kpc in the β = 50 case. Moreover, we find a higher growth rate of the over-densities in the β = 50 run compared to the hydro run. We observe magnetic hills and valleys along the fragmented arms in the β = 50 run, which is characteristic of the Parker instability. [ABSTRACT FROM AUTHOR]

Context. Recent molecular surveys have revealed the rich gas organization of sonic-like filaments at small scales (so-called fibers) in all types of environments prior to the formation of low- and high-mass stars. These fibers form at the end of the turbulent cascade and are identified as the fine substructure within the hierarchical nature of the gas in the interstellar medium (ISM). Aims. Isolated fibers provide the subsonic conditions for the formation of low-mass stars. This paper introduces the Emergence of high-mass stars in complex fiber networks (EMERGE) project, which investigates whether complex fiber arrangements (networks) can also explain the origin of high-mass stars and clusters. Methods. We analyzed the EMERGE Early ALMA Survey including seven star-forming regions in Orion (OMC-1,2,3, and 4 South, LDN 1641N, NGC 2023, and the Flame Nebula) that were homogeneously surveyed in three molecular lines (N2H+J = 1–0, HNC J = 1–0, and HC3N J = 10–9) and in the 3 mm continuum using a combination of interferometric ALMA mosaics and IRAM-30 m single-dish (SD) maps, together with a series of Herschel, Spitzer, and WISE archival data. We also developed a systematic data reduction framework allowing the massive data processing of ALMA observations. Results. We obtained independent continuum maps and spectral cubes for all our targets and molecular lines at different (SD and interferometric) resolutions, and we explored multiple data combination techniques. Based on our low-resolution (SD) observations (30″ or ~12 000 au), we describe the global properties of our sample, which covers a wide range of physical conditions, including low-(OMC-4 South and NGC 2023), intermediate (OMC-2, OMC-3, and LDN 1641N), and high-mass (OMC-1 and Flame Nebula) star-forming regions in different evolutionary stages. The comparison between our single-dish maps and ancillary YSO catalogs denotes N2H+ (1–0) as the best proxy for the dense, star-forming gas in our targets, which show a constant star formation efficiency and a fast time evolution of ≲1 Myr. While apparently clumpy and filamentary in our SD data, all targets show a much more complex fibrous substructure at the enhanced resolution of our combined ALMA+IRAM-30 m maps (4″.5 or ~2000 au). A large number of filamentary features at subparsec scales are clearly recognized in the high-density gas (≳ 105 cm−3) that is traced by N2H+ (1–0) directly connected to the formation of individual protostars. Surprisingly, this complex gas organization appears to extend farther into the more diffuse gas (~103−104 cm−3) traced by HNC (1–0). Conclusions. This paper presents the EMERGE Early ALMA Survey, which includes a first data release of continuum maps and spectral products for this project that are to be analysed in future papers of this series. A first look at these results illustrates the need of advanced data combination techniques between high-resolution interferometric (ALMA) and high-sensitivity, low-resolution single-dish (IRAM-30 m) datasets to investigate the intrinsic multiscale, gas structure of the ISM. [ABSTRACT FROM AUTHOR]

Context. The star formation process leads to an increased chemical complexity in the interstellar medium. Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. Aims. We aim to systematically search for and identify a sample of hot cores toward the 15 Galactic protoclusters of the ALMA-IMF Large Program and investigate their statistical properties. Methods. We built a comprehensive census of hot core candidates toward the ALMA-IMF protoclusters based on the detection of two CH3OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH3OCHO) emission, a complex species commonly observed toward sites of star formation. We performed a cross-matching with the catalog of thermal dust continuum sources from the ALMA-IMF 1.3 mm continuum data to infer their physical properties. Results. We built a catalog of 76 hot core candidates with masses ranging from ~0.2 M⊙ to ~80 M⊙, of which 56 are new detections. A large majority of these objects, identified from methyl formate emission, are compact and rather circular, with deconvolved full width at half maximum (FWHM) sizes of ~2300 au on average. The central sources of two target fields show more extended, but still rather circular, methyl formate emission with deconvolved FWHM sizes of ~6700 au and 13 400 au. About 30% of our sample of methyl formate sources have core masses above 8 M⊙ and range in size from ~1000 au to 13 400 au, which is in line with measurements of archetypical hot cores. The origin of the CH3OCHO emission toward the lower-mass cores may be explained as a mixture of contributions from shocks or may correspond to objects in a more evolved state (i.e., beyond the hot core stage). We find that the fraction of hot core candidates increases with the core mass, suggesting that the brightest dust cores are all in the hot core phase. Conclusions. Our results suggest that most of these compact methyl formate sources are readily explained by simple symmetric models, while collective effects from radiative heating and shocks from compact protoclusters are needed to explain the observed extended CH3OCHO emission. The large fraction of hot core candidates toward the most massive cores suggests that they rapidly enter the hot core phase and that feedback effects from the forming protostar(s) impact their environment on short timescales. [ABSTRACT FROM AUTHOR]

Context. Only indirect evidence of the role of magnetic braking in regulating gravitational collapse and the formation of circumstellar disks, such as compact disk sizes and the launching of high-velocity collimated protostellar jets, has been found from observational work. Aims. More direct tests of the magnetic braking shaping the angular momentum of the gas in Class 0 protostars are crucially needed to confirm and make progress on the magnetically regulated disk formation scenario. Methods. In the present work we used nonideal magnetohydrodynamic models of protostellar collapse and synthetic observations of molecular gas spectral emission, from the radiative transfer post-processing of these models. We analyzed the synthetic observations to test whether possible kinematic signatures of the magnetic braking in the gas velocity field can be captured from maps of the molecular gas emission in protostellar envelopes. Results. By comparing the 3D specific angular momentum of models with varying turbulent energy and magnetization, we show that, in the numerical models of protostellar evolution explored, the increase in magnetization and its consequences on the spatial redistribution of angular momentum modifies the shapes of the radial profiles of specific angular momentum probed along the equatorial plane. However, various analysis of gas kinematics from the synthetic observations of molecular line emission mostly fail to capture the magnitude and differences in radial profiles of specific angular momentum due to different magnetization. Finally, we compare our synthetic observations to observational datasets from the literature to discuss possible magnetic braking signatures in protostellar envelopes. Conclusions. We show that widely used observational methods fail to quantitatively capture the magnitude of angular momentum of the gas in protostellar envelopes, and that no method makes it possible to measure the differences in radial evolution of angular momentum due to different magnetization at all envelope radii. This is especially true in the more magnetized cases where the rotational velocities are of the order of the thermal broadening of the molecular lines. However, our analysis suggests that the detection of symmetric patterns and organized velocity fields in the moment 1 maps of the molecular line emission, and monotonous radial profiles of the specific angular momentum showing a power law decline, should be suggestive of a less magnetized scenario. Protostellar cores where efficient magnetic braking is at work are more likely to present a highly asymmetric velocity field, and more prone to show complex radial profiles of their specific angular momentum measured in the equatorial plane. [ABSTRACT FROM AUTHOR]

Phosphorus plays an essential role in prebiotic chemistry. The origin of P-bearing molecules in the protostellar gas remains highly uncertain. Only PO and PN have been detected towards low-mass star-forming regions and their emission is mainly associated with outflow shocks. In order to make progress in the characterisation of P-chemistry, we present NOEMA observations of PO and PN at 3″−4″ resolution towards the outflow shock region L1157-B1. Our resolved observations confirm the association of both P species with the apex of the bow shock. High-velocity emission is detected in the compact region where the jet impacts the shock. Analysis of the spatial distributions of PO and PN indicates that these molecules are not sputtered from the icy mantles of dust grains; they are the gas-phase products of a P-mother species released in the shock. PO appears to form first in the gas phase, followed by PN, which remains longer in the shock, when PO is no longer detected. Variations of the PO/PN abundance ratio in the range 1–5 are detected over the apex and confirm the short time variability of P-chemistry, which typically lasts a few hundred years. These results are consistent with the previous modelling of P-chemistry in L1157-B1. Complementary observations of N-bearing species at high angular resolution are needed to better understand the formation pathways of PO and PN. [ABSTRACT FROM AUTHOR]

We present synthetic line observations of a simulated molecular cloud, utilizing a self-consistent treatment of the dynamics and time-dependent chemical evolution. We investigate line emission from the three most common CO isotopologues (12CO, 13CO, C18O) and six supposed tracers of dense gas (NH3, HCN, N2H+, HCO+, CS, HNC). Our simulation produces a range of line intensities consistent with that observed in real molecular clouds. The HCN-to-CO intensity ratio is relatively invariant with column density, making HCN (and chemically similar species such as CS) a poor tracer of high-density material in the cloud. The ratio of N2H+ to HCN or CO, on the other hand, is highly selective of regions with densities above |$10^{22} \, {\rm cm}^{-2}$|⁠ , and the N2H+ line is a very good tracer of the dynamics of high volume density (⁠|$\gt 10^4 \, {\rm cm}^{-3}$|⁠) material. Focusing on cores formed within the simulated cloud, we find good agreement with the line intensities of an observational sample of prestellar cores, including reproducing observed CS line intensities with an undepleted elemental abundance of sulphur. However, agreement between cores formed in the simulation, and models of isolated cores which have otherwise-comparable properties, is poor. The formation from and interaction with the large-scale environment has a significant impact on the line emission properties of the cores, making isolated models unsuitable for interpreting observational data. [ABSTRACT FROM AUTHOR]

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

The given text appears to be a correction to a previous paper that examined the relationship between neutron star mass and dark matter accumulation within dark matter clumps. The authors identified an error in their code that resulted in distance measurements being given with respect to the Sun instead of the Galactic center. They corrected the distance values and found that the resulting plots changed, but the results and conclusions remained qualitatively similar. The document includes figures and graphs that illustrate the corrected analysis. [Extracted from the article]

Star formation is generally considered to be 'universal', meaning that it is statistically the same everywhere (and at all times). We investigate whether it is possible to find a simple rule for the conversion of molecular cores into bound stellar systems, along with the resulting secular decay and dynamical destruction of these systems, which can match the field initial mass functions (IMFs) and multiplicity statistics. We find that extreme cases, in which the core fragmentation is self-similar or has a strong dependence on initial core mass, cannot reproduce the observations of the field. However, a model in which core fragmentation is fairly weakly dependent on core mass has some success, if we include the effects of secular decay on the multiplicity statistics. This model both fits the IMF well and has an overabundance of low-mass binary systems over the field that matches local star-forming regions. However, it is unclear whether this overabundance could be dynamically processed to match the field. [ABSTRACT FROM AUTHOR]

In this paper, we report near-infrared observations of the classical T Tauri star TW Hya with the SPIRou high-resolution spectropolarimeter and velocimeter at the 3.6-m Canada–France–Hawaii Telescope in 2019, 2020, 2021, and 2022. By applying Least-Squares Deconvolution (LSD) to our circularly polarized spectra, we derived longitudinal fields that vary from year to year from –200 to +100 G, and exhibit low-level modulation on the 3.6 d rotation period of TW Hya, despite the star being viewed almost pole-on. We then used Zeeman–Doppler Imaging to invert our sets of unpolarized and circularly polarized LSD profiles into brightness and magnetic maps of TW Hya in all four seasons, and obtain that the large-scale field of this T Tauri star mainly consists of a 1.0–1.2 kG dipole tilted at about 20° to the rotation axis, whereas the small-scale field reaches strengths of up to 3–4 kG. We find that the large-scale field is strong enough to allow TW Hya to accrete material from the disc on the polar regions at the stellar surface in a more or less geometrically stable accretion pattern, but not to succeed in spinning down the star. We also report the discovery of a radial velocity signal of semi-amplitude |$11.1^{+3.3}_{-2.6}$| m s−1 (detected at 4.3σ) at a period of 8.3 d in the spectrum of TW Hya, whose origin may be attributed to either a non-axisymmetric density structure in the inner accretion disc, or to a |$0.55^{+0.17}_{-0.13}$| MꝜ candidate close-in planet (if orbiting in the disc plane), at an orbital distance of 0.075 ± 0.001 au. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The detection of Keplerian rotation is rare among Class 0 protostellar systems. We have investigated the high-density tracer HCN as a probe of the inner disc in a Class 0 proto-brown dwarf candidate. Our ALMA high angular resolution observations show the peak in the HCN (3–2) line emission arises from a compact component near the proto-brown dwarf with a small bar-like structure and a deconvolved size of ∼50 au. Radiative transfer modelling indicates that this HCN feature is tracing the innermost, dense regions in the proto-brown dwarf where a small Keplerian disc is expected to be present. The limited velocity resolution of the observations, however, makes it difficult to confirm the rotational kinematics of this feature. A brightening in the HCN emission towards the core centre suggests that HCN can survive in the gas phase in the inner, dense regions of the proto-brown dwarf. In contrast, modelling of the HCO+ (3–2) line emission indicates that it originates from the outer pseudo-disc/envelope region and is centrally depleted. HCN line emission can reveal the small-scale structures and can be an efficient observational tool to study the inner disc properties in such faint compact objects where spatially resolving the disc is nearly impossible. [ABSTRACT FROM AUTHOR]

The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS 4A protobinary system. This analysis is based on ALMA observations of SiO(5–4), H2CO(30, 3–20, 3), and HDCO(41, 4–31, 3) with a spatial resolution of ∼150 au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS 4A1 and IRAS 4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterize the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS 4A1 exhibit extensions of 10 and 13 arcsec with position angles (PA) of 0° and -12°, respectively, while those of IRAS 4A2 are more extended, spanning 18 and 25 arcsec with PAs of 29° and 26°. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events. [ABSTRACT FROM AUTHOR]

Molecular clouds are the prime locations of star formation. These clouds contain filamentary structures and cores which are crucial in the formation of young stars. In this work, we aim to quantify the physical properties of structural characteristics within the molecular cloud L1251 to better understand the initial conditions for star formation. We applied the getsf algorithm to identify cores and filaments within the molecular cloud L1251 using the Herschel multi-band dust continuum image, enabling us to measure their respective physical properties. Additionally, we utilized an enhanced differential term algorithm to produce high-resolution temperature maps and column density maps with a resolution of 13.5 ′ ′ . We identified 122 cores in the region. Of those, 23 are protostellar cores, 13 are robust prestellar cores, 32 are candidate prestellar cores (including 13 robust prestellar cores and 19 strictly candidate prestellar cores), and 67 are unbound starless cores. getsf also found 147 filament structures in the region. Statistical analysis of the physical properties (mass (M), temperature (T), size and core brightness (hereafter, we are using the word luminosity (L)) for the core brightness) of obtained cores shows a negative correlation between core mass and temperature and a positive correlation between (M/L) and (M/T). Analysis of the filaments gives a median width of 0.14 pc and no correlation between width and length. Out of those 122 cores, 92 are present in filaments (∼ 75.4%) and the remaining were outside them. Out of the cores present in filaments, 57 (∼ 62%) cores are present in supercritical filaments ( M line > 16 M ⊙ / pc ). [ABSTRACT FROM AUTHOR]

The spatial–kinematic structure of 48 young star clusters and associations is investigated. Moran's I statistic is used to quantify the degree of kinematic substructure in each region, and the results are compared to those expected assuming the hierarchical or monolithic models of star cluster formation. Of the observed regions, 39 are found to have significant kinematic substructure, such that they are compatible with the hierarchical model and incompatible with the monolithic model. This includes multiple regions whose Q parameter shows the region to be centrally concentrated and clustered. The remaining nine are compatible with both models. From this, it is concluded that the kinematic substructure of the observed star clusters represents strong evidence in favour of the hierarchical model of star cluster formation over the monolithic model. [ABSTRACT FROM AUTHOR]

Molecular clouds are prime locations to study the process of star formation. These clouds contain filamentary structures and cores, which are crucial sites for the formation of young stars. The star-formation process has been investigated using various techniques, including polarimetry, for tracing magnetic fields. In this small review-cum-short report, we put together the efforts (mainly from the Indian community) to understand the roles of turbulence and magnetic fields in star formation. These are two components of the ISM competing against gravity, which is primarily responsible for the collapse of gas to form stars. We also include attempts made using simulations of molecular clouds to study this competition. Studies on feedback and magnetic fields are combined and listed to understand the importance of the interaction between two energies in setting the current observed star formation efficiency. We have listed available and upcoming facilities with the polarization capabilities needed to trace magnetic fields. We have also stated the importance of ongoing and desired collaborations between Indian communities and facilities abroad to shed more light on the roles of turbulence and magnetic fields in the process of star formation. [ABSTRACT FROM AUTHOR]

We present a comprehensive investigation on the mass function (MF) of a snake-like stellar structure in the solar neighbourhood, building on our previous discovery. To ensure the reliability of the data, we reselect the member stars of the Stellar 'Snake' in the latest Gaia Data Release 3 using the same approach as the initial series of articles. We also precisely measure the physical parameters of the clusters within the Stellar Snake. In light of the high completeness of the member stars in the cluster regions, we develop a simulated model colour–magnitude diagram-based inference method to derive the mass function, binary fraction, and mass-ratio distribution of the clusters in the Stellar Snake. Notably, despite their similar ages and metallicity, we discover systematic variations in the MFs along the elongation direction of the Snake in the mass range of 0.5 to 2.0 M⊙. The 'head' of the Snake conforms to a canonical initial mass function with a power-law slope of α ∼ −2.3. Extending towards the 'tail', the MF becomes more top-light, indicating a deficiency of massive stars within these clusters. This result provides evidence for the delayed formation of massive stars in the clusters. Such clues give support to the hypothesis that the Stellar Snake constitutes as a hierarchically primordial structure. [ABSTRACT FROM AUTHOR]

We have investigated the physical properties of Planck Galactic Cold Clumps (PGCCs) located in the Galactic Plane, using the JCMT Plane Survey (JPS) and the SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE) survey. By utilizing a suite of molecular-line surveys, velocities, and distances were assigned to the compact sources within the PGCCs, placing them in a Galactic context. The properties of these compact sources show no large-scale variations with Galactic environment. Investigating the star-forming content of the sample, we find that the luminosity-to-mass ratio (L / M) is an order of magnitude lower than in other Galactic studies, indicating that these objects are hosting lower levels of star formation. Finally, by comparing ATLASGAL sources that are associated or are not associated with PGCCs, we find that those associated with PGCCs are typically colder, denser, and have a lower L / M ratio, hinting that PGCCs are a distinct population of Galactic Plane sources. [ABSTRACT FROM AUTHOR]

The chemistry of H2O, CO, and other small molecular species in an isolated pre-stellar core, L1544, has been assessed in the context of a comprehensive gas-grain chemical model, coupled to an empirically constrained physical/dynamical model. Our main findings are (i) that the chemical network remains in near equilibrium as the core evolves towards star formation and the molecular abundances change in response to the evolving physical conditions. The gas-phase abundances at any time can be calculated accurately with equilibrium chemistry, and the concept of chemical clocks is meaningless in molecular clouds with similar conditions and dynamical time-scales, and (ii) A comparison of the results of complex and simple chemical networks indicates that the abundances of the dominant oxygen and carbon species, H2O, CO, C, and C+ are reasonably approximated by simple networks. In chemical equilibrium, the time-dependent differential terms vanish, and a simple network reduces to a few algebraic equations. This allows rapid calculation of the abundances most responsible for spectral line radiative cooling in molecular clouds with long dynamical time-scales. The dust ice mantles are highly structured and the ice layers retain a memory of the gas-phase abundances at the time of their deposition. A complex (gas-phase and gas-grain) chemical structure therefore exists, with cosmic-ray induced processes dominating in the inner regions. The inferred H2O abundance profiles for L1544 require that the outer parts of the core and also any medium exterior to the core are essentially transparent to the interstellar radiation field. [ABSTRACT FROM AUTHOR]

During the last decade, cosmological simulations have managed to reproduce realistic and morphologically diverse galaxies, spanning the Hubble sequence. Central to this success was a phenomenological calibration of the few included feedback processes, while glossing over higher complexity baryonic physics. This approach diminishes the predictive power of such simulations, preventing to further our understanding of galaxy formation. To tackle this fundamental issue, we investigate the impact of cosmic rays (CRs) and magnetic fields on the interstellar medium and the launching of outflows in a cosmological zoom-in simulation of a Milky Way-like galaxy. We find that including CRs decreases the stellar mass of the galaxy by a factor of 10 at high redshift and ∼4 at cosmic noon, leading to a stellar mass to halo mass ratio in good agreement with abundance matching models. Such decrease is caused by two effects: (i) a reduction of cold, high-density, star-forming gas, and (ii) a larger fraction of supernova (SN) events exploding at lower densities, where they have a higher impact. SN-injected CRs produce enhanced, multiphase galactic outflows, which are accelerated by CR pressure gradients in the circumgalactic medium of the galaxy. While the mass budget of these outflows is dominated by the warm ionized gas, warm neutral and cold gas phases contribute significantly at high redshifts. Importantly, our work shows that future JWST observations of galaxies and their multiphase outflows across cosmic time have the ability to constrain the role of CRs in regulating star formation. [ABSTRACT FROM AUTHOR]