We investigated the kinematics and dynamics of gas structures on galaxy-cloud scales in two spiral galaxies NGC5236 (M83) and NGC4321 (M100) using CO (2$-$1) line. We utilised the FILFINDER algorithm on integrated intensity maps for the identification of filaments in two galaxies. Clear fluctuations in velocity and density were observed along these filaments, enabling the fitting of velocity gradients around intensity peaks. The variations in velocity gradient across different scales suggest a gradual and consistent increase in velocity gradient from large to small scales, indicative of gravitational collapse, something also revealed by the correlation between velocity dispersion and column density of gas structures. Gas structures at different scales in the galaxy may be organised into hierarchical systems through gravitational coupling. All the features of gas kinematics on galaxy-cloud scale are very similar to that on cloud-clump and clump-core scales studied in previous works. Thus, the interstellar medium from galaxy to dense core scales presents multi-scale/hierarchical hub-filament structures. Like dense core as the hub in clump, clump as the hub in molecular cloud, now we verify that cloud or cloud complex can be the hub in spiral galaxies. Although the scaling relations and the measured velocity gradients support the gravitational collapse of gas structures on galaxy-cloud scales, the collapse is much slower than a pure free-fall gravitational collapse.

Measurement of internal structures in the prestellar core is essential for understanding the initial conditions prior to star formation. In this work, we study the ammonia lines (NH$_{3}$) (J, K = 1,1 and 2,2) in the central region of the prestellar core L1517B with the Karl G. Jansky Very Large Array (VLA) radio telescope (spatial resolution $\sim$ 3.7′′). Our analysis indicates that the central region of the core is close-to-round in shape obtained both from NH$_{3}$ (1,1) and (2,2) emissions. Radially averaged kinetic temperature ($T_{k}$) is almost constant with a mean value of $\sim$ 9 K. A radially sharp decrease in kinetic temperature ($T_{k}$) has not been observed inside the central dense nucleus of this prestellar core. In addition, we also notice that there is an overall velocity gradient from north-east to south-west direction in this region, which may be indicative of the rotational motion of the core. We then calculate the parameter $\beta$, which is defined as the ratio of rotational energy to gravitational potential energy and find that $\beta$ equals to $\sim$ 5 $\times$ 10$^{-3}$; which indicates that rotation has no effect at least inside the central region of the core. We also perform the viral analysis and observe that the central region may be in a stage of contraction. From this study, we also show that turbulence inside the central region is subsonic in nature (sonic Mach number, $M_{s}$ $<$ 1) and has no prominent length-scale dependence. Furthermore, we notice that the decrement of excitation temperature ($T_{ex}$) and column density of NH$_{3}$ from the centre of the core to the outer side with the peak values of $\sim$ 5.6 K and $\sim$ 10$^{15}$ cm$^{-2}$, respectively. In conclusion, this work examines different physical and kinematical properties of the central region of the L1517B prestellar core.

We study the correlation between the non-thermal velocity dispersion ($\sigma_{nth}$) and the length scale (L) in the neutral interstellar medium (ISM) using a large number of Hi gas components taken from various published Hi surveys and previous Hi studies. We notice that above the length-scale (L) of 0.40 pc, there is a power-law relationship between $\sigma_{nth}$ and L. However, below 0.40 pc, there is a break in the power law, where $\sigma_{nth}$ is not significantly correlated with L. It has been observed from the Markov chain Monte Carlo (MCMC) method that for the dataset of L $\gt$ 0.40 pc, the most probable values of intensity (A) and power-law index (p) are 1.14 and 0.55, respectively. Result of p suggests that the power law is steeper than the standard Kolmogorov law of turbulence. This is due to the dominance of clouds in the cold neutral medium. This is even more clear when we separate the clouds into two categories: one for L is $\gt$ 0.40 pc and the kinetic temperature ($T_{k}$) is $\lt$250 K, which are in the cold neutral medium (CNM) and for other one where L is $\gt$0.40 pc and $T_{k}$ is between 250 and 5 000 K, which are in the thermally unstable phase (UNM). Most probable values of A and p are 1.14 and 0.67, respectively, in the CNM phase and 1.01 and 0.52, respectively, in the UNM phase. A greater number of data points is effective for the UNM phase in constructing a more accurate estimate of A and p, since most of the clouds in the UNM phase lie below 500 K. However, from the value of p in the CNM phase, it appears that there is a significant difference from the Kolmogorov scaling, which can be attributed to a shock-dominated medium.

The protostellar environment where young stars form has physical conditions suitable to excite a number of molecular maser lines that have traditionally provided an unique probe of star formation kinematics, at the highest angular resolution of radio very long baseline interferometry (VLBI) observations. In the following, we will discuss a number of recent results on our understanding of the gas dynamics traced by masers in the vicinity of young forming stars. These findings provide direct clues on how our community can substantially contribute to the field of star formation in the next decade.

We are investigating the extended outflow from G25.82–W1, which is one of the members of the high-mass protocluster G25.82–0.17. The aim is to study the star-forming environment of G25.82–W1. To identify the outflow, we obtained CO 2-1 data using the Atacama Large Millimeter/submillimeter Array.

We have identified several spatial and spectral outflows, including: 1) an extended N1–S1 CO outflow, driven by a high-mass young stellar object (HM-YSO) named G25.82–W1; 2) an elongated SE–NW outflow powered by G25.82–W2; 3) a compact and curved N2–S2 CO outflow originating from G25.82–E; and 4) a pair of knotty lobes centered on G25.82–W.

Furthermore, the innermost region of the N1–S1 CO outflow, traced by the 22 GHz H2O maser, reveals a complex spatial and velocity structure within a 2” from its launching point.

To accurately calculate the properties of the N1–S1 CO outflow, we have utilized an accurate distance measurement of d=4.5 kpc, derived from the annual parallax of the H2O masers. The outflow rate and force are comparable to those observed in outflows from other HM-YSOs. The physical properties of the N1–S1 CO outflow follow a trend connecting the low and high-mass regimes, supporting the idea that the star-forming mode in G25.82–W1 is likely a scaled-up version of low-mass star formation.

Context: Theoretical scenarios describe the phenomenon of mass accumulation by high-mass young stellar objects (HMYSOs) through disk accretion. Aims: To find out whether the rotation of the core around hyper-compact (HC) HII regions is common Methods: The molecular core G301.1364-00.2249A was selected as the subject of investigation. Observations were carried out on CH3CN, SO2, H29α radio recombination line and continuum emission. Analysis involved the “Moment 0, 1, 2" and “Population-diagram” methods. Result: The structures of G301.1364-00.2249A exhibited clear definition. CH3CN moment 0 images revealed multiple enhanced emission regions and an absorption area. The moment 1 image depicted a velocity gradient from southeast to northwest. Conclusion: The molecular gas has a rotational motion in the direction from the southeast to northwest. The rotational temperature was measured at 293 K.

This is a multi-wavelength study to examine the G45.804-0.355 massive star-forming region (SFR) and its environs. Using MeerKAT with angular resolution (θ) of 8″ at 1.28 GHz, we identify for the first time, a faint radio continuum emission core in G45.804-0.355. At 1.3 mm, ALMA observations (θ∼0″ 7) resolved the core into multiple dust continuum condensations including MM1 which was found to be the primary massive dust dense core in the region (mass Mc∼ 54.3M⊙). The dust continuum shows an arm-like extended emission within which other dense cores are situated. The velocity gradient of the MM1 core indicates that the source is associated with a rotation gas motion. The red- and blue-shifted lobes overlap at the position of MM1. The compact morphology of the 4.5 μm IR emission, the presence of spiral arms and overlapping of the red- and blue-shifted lobes suggest a face-on geometry of G45.80-40.355.

Disk-jet systems are common in astrophysical sources of different nature, from black holes to gaseous giant planets. The disk drives the mass accretion onto a central compact object and the jet ejects material along the disk rotation axis. Magnetohydrodynamic disk winds can provide the link between mass accretion and ejection, which is essential to ensure that the excess angular momentum is removed and accretion can proceed. However, up to now, we have been lacking direct observational proof of disk winds. This work presents a direct view of the velocity field of a disk wind around a forming massive star. Achieving a very high spatial resolution of 0.05 au, our water maser observations trace the velocities of individual streamlines emerging from the disk orbiting the forming star. We find that, at low elevation above the disk midplane, the flow co-rotates with its launch point in the disk, in agreement with magneto-centrifugal acceleration. Beyond the co-rotation point, the flow rises spiraling around the disk rotation axis along a helical magnetic field. We have performed (resistive-radiative-gravito-) magnetohydrodynamic simulations of the formation of a massive star and record the development of a magneto-centrifugally launched jet presenting many properties in agreement with our observations.

Even though galactic winds are common in galaxies with starbursts or active galactic nuclei (AGN), the role of such gas flows in galaxy evolution remains uncertain. Here we examine how winds vary along a likely evolutionary sequence connecting starburst to post-starburst to quiescent galaxies. To detect the interstellar medium and measure its bulk flows, we examine the residual Na D absorption line doublet after the stellar contribution has been removed from each galaxy’s spectrum. We discover that outflows diminish along this sequence, i.e., as star formation ends. We then focus on the wind behavior within the post-starburst sample, for which we have measured the time elapsed since the starburst ended (post-burst age) via detailed modeling of their star formation histories (French et al.2018). Even within our post-starburst sample, the fraction of galaxies with significant winds and the average wind velocities decrease with post-burst age after controlling for stellar mass.

We have carried out ALMA observations toward the environments of G333.0162+00.7615 which was considered as a candidate of high-mass young stellar object (HMYSO) in previous studies. Our dust continuum, molecular line emission and radio recombination line emission observations show that this source is not HMYSO associated with hypercompact (HC) HII regions. Instead, we discovered two new hot cores associate with earliest stages of high mass star formation region. We estimated the rotational temperatures of these cores about 270 K from J=14→13 rotational transition of CH3CN ladder. The moment maps show velocity gradients confirming that this cores are rotating.

We employ the Feedback In Realistic Environments (FIRE-2) physics model to study how the properties of giant molecular clouds (GMCs) evolve during galaxy mergers. Due to the rarity of mergers in the local Universe, samples of nearby merging galaxies suitable for studies of individual GMCs are limited. Idealized simulations provide us with a new window to study GMC evolution during a merger, and assist in interpreting observations. We conduct a pixel-by-pixel analysis of the simulated molecular gas properties in both undisturbed control galaxies and galaxy mergers. The simulated GMC-pixels follow a similar trend in a diagram of velocity dispersion (σv) versus gas surface density (Σmol) as observed in normal spiral galaxies in the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey. For simulated mergers, we see a significant increase in both the Σmol and σv for GMC-pixels by a factor of 5 – 10, which put these pixels to be above the trend of PHANGS galaxies in the σv vs Σmol diagram. This deviation indicates that GMCs in the simulated merger are more gravitationally unbound and have higher virial parameter (αvir) of 10 – 100, which is much larger than that of simulated control galaxies. Furthermore, we find that the increase in αvir generally happens at the same time as the increase in global star formation rate (SFR), which suggests feedback is playing a role in dispersing the gas. The correspondence between high αvir and SFR also suggests some other physical mechanisms besides self-gravity are helping the GMCs in starburst mergers to collapse and form stars.

The Sun moves with respect to the local interstellar medium (LISM) and modifies its properties to heliocentric distances as large as 1 pc. The solar wind (SW) is affected by penetration of the LISM neutral particles, especially H and He atoms. Charge exchange between the LISM atoms and SW ions creates pickup ions (PUIs) and secondary neutral atoms that can propagate deep into the LISM. Neutral atoms measured at 1 au can provide us with valuable information on the properties of pristine LISM. Voyager 1 and 2 spacecraft perform in situ measurements of the LISM perturbed by the presence of the heliosphere and relate them to the unperturbed region. We discuss observational data and numerical simulations that shed light onto the mutual influence of the SW and LISM. Physical phenomena accompanying the SW–LISM interaction are discussed, including the coupling of the heliospheric and interstellar magnetic field at the heliopause.

Thanks to deep optical to near-IR imaging and spectroscopy, significant progress is made in characterizing the rest-frame UV to optical properties of galaxies in the early universe (z > 4. Surveys with Hubble, Spitzer, and ground-based facilities (Keck, Subaru, and VLT) provide spectroscopic and photometric redshifts, measurements of the spatial structure, stellar masses, and optical emission lines for large samples of galaxies. Recently, the Atacama Large (Sub) Millimeter Array (ALMA) has become a major player in pushing studies of high redshift galaxies to far-infrared wavelengths, hence making panchromatic surveys over many orders of frequencies possible. While past studies focused mostly on bright sub-millimeter galaxies, the sensitivity of ALMA now enables surveys like ALPINE, which focuses on measuring the gas and dust properties of a large sample of normal main-sequence galaxies at z > 4. Combining observations across different wavelengths into a single, panchromatic picture of galaxy formation and evolution is currently and in the future an important focus of the astronomical community.

The pore structure of vapour deposited ASW is poorly understood, despite its importance to fundamental processes such as grain chemistry, cooling of star forming regions, and planet formation. We studied structural changes of vapour deposited D2O on intra-molecular to 30 nm length scales at temperatures ranging from 18 to 180 K and observed enhanced mobility from 100 to 150 K. An Arrhenius type model describes the loss of surface area and porosity with a common set of kinetic parameters. The low activation energy (428 K) is commensurate with van der Waals forces between nm-scale substructures in the ice. Our findings imply that water porosity will always change with time, even at low temperatures.

Complex organic molecules (COMs) may have played a role in the formation of life in the early Earth (Herbst & van Dishoeck (2009)). Here we present the formation of NH2CHO and CH3CHO upon vacuum-ultraviolet (VUV) irradiation of CO:NH3 and CO:CH4 ice mixtures, simulating the UV processing of interstellar ices in the interior of dense clouds. We have found that the conversion from ${\rm{N}}{{\rm{H}}_{\dot 2}}$ radicals to NH2CHO is 4–15 times higer than that from ${\rm{N}}{{\rm{H}}_{\dot 3}}$ to CH3CHO, probably due to the competing formation of larger hydrocarbons in the latter case.

Star formation started as a cosmic process soon after the big bang and still continues in the Milky Way, although at a decreasing rate. The formation of dense interstellar clouds, their fragmentation and eventual collapse lead to the birth of stars. The nearby clouds provide the highest resolution for the study of this process. The progress is closely following the improvement of the infrared and radio-wavelength facilities that enables us to follow even the earliest stages of the star-formation process inside molecular clouds. On the other hand, modern numerical simulations can take into account most of the relevant physics and often provide a more direct access into the general principles of star formation. The comparison of observations and simulations is therefore essential. In this paper, will discuss star formation in the solar neighbourhood, concentrating on the prestellar phases leading up to the formation of protostars.

Meteoritic evidence shows that the Solar system at birth contained significant quantities of short-lived radioisotopes (SLRs) such as 60Fe and 26Al produced in supernova explosions and in the Wolf-Rayet winds. Explaining how they travelled from these origin sites to the primitive Solar system before decaying is an outstanding problem. In this paper, we present a chemo-hydrodynamical simulation of the entire Milky Way to measure for the distribution of 60Fe/56Fe and 26Al/27Al ratios over all stars in the Galaxy. We show that the Solar abundance ratios are well within the normal range. We find that SLRs are abundant in newborn stars because star formation is correlated on Galactic scales, so that ejecta preferentially enrich atomic gas that will subsequently be accreted onto existing GMCs or will form new ones. Thus new generations of stars preferentially form in patches of the Galaxy contaminated by previous generations of stellar feedback.

Our ALMA observations of HCO+ and HCN show such redshifted absorption toward an isolated core, BHR 71. Both lines show a similar redshifted absorption profile. We also found emissions of complex organic molecules (COMs) around 345 GHz from a compact region centered on the continuum source, which is barely resolved with a beam of 0″27, corresponding to ∼50 AU.

The connection between low- and high-mass filaments is a matter of strong debate. In order to bridge these two filamentary regimes, we have investigated the internal structure of the Integral Filament in Orion using ALMA observations of the N2H+ (1-0) emission line in Band 3 in combination with previous single-dish data. Our ALMA mosaics, the largest of its kind carried out so-far in local clouds, reveal the presence of multiple sonic-like fibers inside this massive filament. In combination with the identification of fibers in regions such as Taurus, Musca, and Perseus, the first unambiguous detection of fibers in Orion highlights the importance of these gas substructures as the fundamental building blocks of both low- and high-mass filaments.

PNe are known to be photoionized objects. However they also have low-ionization structures (LIS) with different excitation behavior. We are only now starting to answer why most LIS have lower electron densities than the PN shells hosting them, and whether or not their intense emission in low-ionization lines is the key to their main excitation mechanism. Can LIS line ratios, chemical abundances and kinematics enlight the interplay between the different excitation and formation processes in PNe? Based on the spectra of five PNe with LIS and using new diagnostic diagrams from shock models, we demonstrate that LIS’s main excitation is due to shocks, whereas the other components are mainly photoionized. We propose new diagnostic diagrams involving a few emission lines ([N II], [O III], [S II]) and fshocks/f*, where fshocks and f* are the ionization photon fluxes due to the shocks and to the central star ionizing continuum, respectively.