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Hydrogen radio recombination lines (RRLs) are one of the major diagnostics of the physical properties of H  ii regions. We use RRL H40α, He40α, and 3 mm continuum emission to investigate the properties of a large sample of resolved UC H  ii regions identified in the ATOMS survey. In total, we identify 94 UC H  ii regions from H40α emission. The basic parameters for these UC H  ii regions, such as electron density, emission measure, electron temperature, ionic abundance ratio (n |$_{\rm He^+}$| /n |$_{\rm H^+}$|⁠), and line width are derived. The median electron density and the median n |$_{\rm He^+}$| /n |$_{\rm H^+}$| ratio of these UC H  ii regions derived from RRLs are ∼9000 cm−3 and 0.11, respectively. Within UC H  ii regions, the n |$_{\rm He^+}$| /n |$_{\rm H^+}$| ratios derived from the intensity ratio of the He40α and H40α lines seems to be higher in the boundary region than in the centre. The H40α line width is mainly broadened by thermal motion and microturbulence. The electron temperature of these UC H  ii regions has a median value of ∼6700 K, and its dependence on galactocentric distance is weak. [ABSTRACT FROM AUTHOR]

Investigating the physical and chemical structure of massive star-forming regions is critical for understanding the formation and early evolution of massive stars. We performed a detailed line survey toward six dense cores, named MM1, MM4, MM6, MM7, MM8, and MM11, in the G9.62+0.19 star-forming region resolved in Atacama Large Millimeter/submillimeter Array (ALMA) band 3 observations. Toward these cores, about 172 transitions have been identified and attributed to 16 species, including organic oxygen-, nitrogen-, and sulphur-bearing molecules and their isotopologues. Four dense cores, MM7, MM8, MM4, and MM11, are line-rich sources. Modelling of these spectral lines reveals that the rotational temperature lies in the range 72–115, 100–163, 102–204, and 84–123 K for MM7, MM8, MM4, and MM11, respectively. The molecular column densities are 1.6 × 1015–9.2 × 1017 cm−2 toward the four cores. The cores MM8 and MM4 show a chemical difference between oxygen- and nitrogen-bearing species, i.e. MM4 is rich in oxygen-bearing molecules, while nitrogen-bearing molecules, especially vibrationally excited HC3N lines, are mainly observed in MM8. The distinct initial temperatures at the accretion phase may lead to this N/O differentiation. Through analysing column densities and spatial distributions of O-bearing complex organic molecules (COMs), we found that C2H5OH and CH3OCH3 might have a common precursor, CH3OH. CH3OCHO and CH3OCH3 are likely chemically linked. In addition, the observed variation in HC3N and HC5N emission may indicate their different formation mechanisms in hot and cold regions. [ABSTRACT FROM AUTHOR]

To understand the nature of SiO emission, we conducted ACA observations of the SiO (2-1) lines toward 146 massive star-forming regions, as part of the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey. We detected SiO emission in 128 (87.7 |${{\ \rm per\ cent}}$|⁠) sources and identified 171 SiO clumps, 105 of which are spatially separated from 3 mm continuum emission. A large amount of the SiO line profiles (60 |${{\ \rm per\ cent}}$|⁠) are non-Gaussian. The velocity dispersion of the SiO lines ranges from 0.3 to 5.43 km s−1. In 63 sources the SiO clumps are associated with H  ii regions characterized by H40α emission. We find that 68 |${{\ \rm per\ cent}}$| (116) of the SiO clumps are associated with strong outflows. The median velocity dispersion of the SiO line for outflow sources and non-outflow sources is 1.91 km s−1 and 0.99 km s−1, respectively. These results indicate that outflow activities could be connected to strongly shocked gas. The velocity dispersion and [SiO]/[H13CO+] intensity ratio do not show any correlation with the dust temperature and particle number density of clumps. We find a positive correlation between the SiO line luminosity and the bolometric luminosity, implying stronger shock activities are associated with more luminous protoclusters. The SiO clumps in associations with H  ii regions were found to show a steeper feature in |$L_{\rm{sio}}$| / |$L_{\rm{bol}}$|⁠. The SiO line luminosity and the fraction of shocked gas have no apparent evidence of correlation with the evolutionary stages traced by luminosity to mass ratio (⁠|$L_{\rm{bol}}/M$|⁠). [ABSTRACT FROM AUTHOR]

With the aim of understanding the role of outflows in star formation, we performed a statistical study of the physical parameters of outflows in 11 massive protoclusters associated with ultracompact H  ii regions. A total of 106 outflow lobes are identified in these protoclusters using the ALMA CO (3–2), HCN (4–3), and HCO+ (4–3) line observations. Although the position angles of outflow lobes do not differ in these three tracers, HCN and HCO+ tend to detect lower terminal velocity of the identified outflows compared to CO. The majority of the outflows in our targets are young with typical dynamical time-scales of 102–104 yr, and are mostly composed of low-mass outflows along with at least one high-mass outflow in each target. An anticorrelation of outflow rate with dynamical time-scale indicates that the outflow rate possibly decreases with time. Also, a rising trend of dynamical time-scale with the mass of the associated core hints that the massive cores might have longer accretion histories than the low-mass cores. Estimation of different energies in these protoclusters shows that outflows studied here cannot account for the generation of the observed turbulence, but can sustain the turbulence at the current epoch as the energy injection rate from the outflows is similar to the estimated dissipation rate. [ABSTRACT FROM AUTHOR]

We have analysed the chemical and kinematic properties of the 20 and 50 km s-1 molecular clouds in the Central Molecular Zone of the Milky Way Galaxy, as well as those of the molecular ridge bridging these two clouds. Our work has utilized 37 molecular transitions in the 0.65, 3 and 7-mm wavebands, from the Mopra and NANTEN2 telescopes. The 0.65-mm NANTEN2 data highlights a dense condensation of emission within the western part of the 20 km s-1 cloud, visible in only four other transitions, which are 3-mm H13CN (1-0), H13CO+ (1-0), HNC (1-0) and N2H+ (1-0), suggesting that the condensation is moderately optically thick and cold. We find that while the relative chemical abundances between both clouds are alike in many transitions, suggesting little variation in the chemistry between both clouds; the 20 km s-1, cold cloud is brighter than the 50 km s-1 cloud in shock and high density tracers. The spatial distribution of enhanced emission is widespread in the 20 km s-1 cloud, as shown via line ratio maps. The position velocity diagrams across both clouds indicate that the gas is well mixed. We show that the molecular ridge is most likely part of the 20 km s-1 cloud and that both of them may possibly extend to include the 50 km s-1 cloud, as part of one larger cloud. Furthermore, we expect that the 20 km s-1 cloud is being tidally sheared as a result of the gravitational potential from Sgr A*. [ABSTRACT FROM AUTHOR]

We present a 30-50 GHz survey of Sagittarius B2(N) conducted with the Australia Telescope Compact Array with ~5-10 arcsec resolution. This work releases the survey data and demonstrates the utility of scripts that perform automated spectral line fitting on broad-band line data. We describe the line-fitting procedure, evaluate the performance of the method, and provide access to all data and scripts. The scripts are used to characterize the spectra at the positions of three H II regions, each with recombination line emission and molecular line absorption. Towards the most line-dense of the three regions characterized in this work, we detect ~500 spectral line components of which ~90 percent are confidently assigned to H and He recombination lines and to 53 molecular species and their isotopologues. The data reveal extremely sub-thermally excited molecular gas absorbing against the continuum background at two primary velocity components. Based on the line radiation over the full spectra, the molecular abundances and line excitation in the absorbing components appear to vary substantially towards the different positions, possibly indicating that the two gas clouds are located proximate to the star-forming cores instead of within the envelope of Sgr B2. Furthermore, the spatial distributions of species including CS, OCS, SiO, and HNCO indicate that the absorbing gas components likely have high UV-flux. Finally, the data contain line-of-sight absorption by ~15 molecules observed in translucent gas in the Galactic Centre, bar, and intervening spiral arm clouds, revealing the complex chemistry and clumpy structure of this gas. Formamide (NH2CHO) is detected for the first time in a translucent cloud. [ABSTRACT FROM AUTHOR]