https://nova.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:34944 + (1–0) line for the "blue asymmetry" spectroscopic signature of infall motion in a large sample of high-mass, dense molecular clumps observed to be at different evolutionary stages of star cluster formation according to their mid-infrared appearance. To quantify the degree of the line asymmetry, we measure the asymmetry parameter A=[formula could not be replicated], the fraction of the integrated intensity that lies to the blueshifted side of the systemic velocity determined from the optically thin tracer N₂H⁺ (1–0). For a sample of 1093 sources, both the mean and median of A are positive (A=0.0830 ± 010 and 0.065 ± 0.009, respectively) with high statistical significance, and a majority of sources (a fraction of 0.607 ± 0.015 of the sample) show positive values of A, indicating a preponderance of blue asymmetric profiles over red asymmetric profiles. Two other measures, the local slope of the line at the systemic velocity and the δv parameter of Mardones et al. (1997), also show an overall blue asymmetry for the sample, but with smaller statistical significance. This blue asymmetry indicates that these high-mass clumps are predominantly undergoing gravitational collapse. The blue asymmetry is larger (A ∼ 0.12) for the earliest evolutionary stages (quiescent, protostellar, and compact H ii region) than for the later H ii region (A ∼ 0.06) and photodissociation region (A ∼ 0) classifications.]]> Tue 03 Sep 2019 17:57:00 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:34952 ⊙), cold (14 K) 3.6–70 μm dark IRDC, G331.372-00.116. This infrared dark cloud (IRDC) has the potential to form high-mass stars, and given the absence of current star formation signatures, it seems to represent the earliest stages of high-mass star formation. We have mapped the whole IRDC with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.1 and 1.3 mm in dust continuum and line emission. The dust continuum reveals 22 cores distributed across the IRDC. In this work, we analyze the physical properties of the most massive core, ALMA1, which has no molecular outflows detected in the CO (2–1), SiO (5–4), and H₂CO (3–2) lines. This core is relatively massive (M = 17.6 M _⊙), subvirialized (virial parameter α _vir = M_vir/M = 0.14), and is barely affected by turbulence (transonic Mach number of 1.2). Using the HCO⁺ (3–2) line, we find the first detection of infall signatures in a relatively massive, prestellar core (ALMA1) with the potential to form a high-mass star. We estimate an infall speed of 1.54 km s⁻¹ and a high accretion rate of 1.96 × 10⁻³ M _⊙ yr⁻¹. ALMA1 is rapidly collapsing, out of virial equilibrium, which is more consistent with competitive accretion scenarios rather than the turbulent core accretion model. On the other hand, ALMA1 has a mass ~6 times larger than the clumps Jeans mass, as it is in an intermediate mass regime (M_J = 2.7 ⊙), contrary to what both the competitive accretion and turbulent core accretion theories predict.]]> Tue 03 Sep 2019 17:56:50 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:45526 J = 4(0, 4) − 3(0, 3) data at 3 mm, using two new pieces of software that we make available to the community. First, SCOUSEPY, a Python implementation of the spectral line fitting algorithm SCOUSE. Secondly, ACORNS (Agglomerative Clustering for ORganising Nested Structures), a hierarchical n-dimensional clustering algorithm designed for use with discrete spectroscopic data. Together, these tools provide an unbiased measurement of the line-of-sight velocity dispersion in this cloud, σ_vlos,1D=4.4±2.1 km s⁻¹, which is somewhat larger than predicted by velocity dispersion-size relations for the central molecular zone (CMZ). The dispersion of centroid velocities in the plane of the sky are comparable, yielding σ_vlos,1D/σ_vpos,1D∼1.2±0.3⁠. This isotropy may indicate that the line-of-sight extent of the cloud is approximately equivalent to that in the plane of the sky. Combining our kinematic decomposition with radiative transfer modelling, we conclude that G0.253+0.016 is not a single, coherent, and centrally condensed molecular cloud; ‘the Brick’ is not a brick. Instead, G0.253+0.016 is a dynamically complex and hierarchically structured molecular cloud whose morphology is consistent with the influence of the orbital dynamics and shear in the CMZ.]]> Thu 03 Nov 2022 12:56:08 AEDT ]]>