https://nova.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:31211 Wed 11 Apr 2018 17:23:17 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:33990 Wed 04 Sep 2019 09:48:58 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:52899 Tue 31 Oct 2023 15:46:12 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:38595 L_{[C II]}/L_FIR, varies by a factor of at least 140 among these four clumps. In particular, for AGAL313.576+0.324, no [C II] line emission is detected despite a FIR luminosity of 24,000 L. AGAL313.576+0.324 lies a factor of more than 100 below the empirical correlation curve between L_{[C II]}/L_FIR and S_v (63 μm) S_v (158 μm) found for galaxies. AGAL313.576+0.324 may be in an early evolutionary “protostellar” phase with insufficient ultraviolet flux to ionize carbon, or in a deeply embedded “‘hypercompact” H II region phase where dust attenuation of UV flux limits the region of ionized carbon to undetectably small volumes. Alternatively, its apparent lack of [C II] emission may arise from deep absorption of the [C II] line against the 158 μm continuum, or self-absorption of brighter line emission by foreground material, which might cancel or diminish any emission within the FIFI-LS instrument’s broad spectral resolution element (AV ~ 250 km s⁻¹).]]> Tue 16 Nov 2021 15:25:30 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:34083 ⊙), cold (12 K), and 3.6–70 μm IR dark clump (MM1) that has the potential to form high-mass stars. We observed this prestellar clump candidate with the Submillimeter Array (~3".5 resolution) and Jansky Very Large Array (~2farcs1 resolution) in order to characterize the early stages of high-mass star formation and to constrain theoretical models. Dust emission at 1.3 mm wavelength reveals five cores with masses ≤15 M_⊙. None of the cores currently have the mass reservoir to form a high-mass star in the prestellar phase. If the MM1 clump will ultimately form high-mass stars, its embedded cores must gather a significant amount of additional mass over time. No molecular outflows are detected in the CO (2-1) and SiO (5-4) transitions, suggesting that the SMA cores are starless. By using the NH₃ (1, 1) line, the velocity dispersion of the gas is determined to be transonic or mildly supersonic (ΔV_nt/ΔV_th ~ 1.1–1.8). The cores are not highly supersonic as some theories of high-mass star formation predict. The embedded cores are four to seven times more massive than the clump thermal Jeans mass and the most massive core (SMA1) is nine times less massive than the clump turbulent Jeans mass. These values indicate that neither thermal pressure nor turbulent pressure dominates the fragmentation of MM1. The low virial parameters of the cores (0.1–0.5) suggest that they are not in virial equilibrium, unless strong magnetic fields of ~1–2 mG are present. We discuss high-mass star formation scenarios in a context based on IRDC G028.23-00.19, a study case believed to represent the initial fragmentation of molecular clouds that will form high-mass stars.]]> Tue 03 Sep 2019 18:23:32 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:34949 1,6–5_2,3 maser line at 22.235 GHz, and several other molecular lines. We present a representative portion of the data from the pilot survey, including NH₃(1,1) and NH₃(2,2) integrated intensity maps, H₂O maser positions, maps of NH₃ velocity, NH₃ line width, total NH₃ column density, and NH₃ rotational temperature. These data and the data cubes from which they were produced are publicly available on the RAMPS website (http://sites.bu.edu/ramps/).]]> Tue 03 Sep 2019 18:17:26 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:34924 10⁴ M_⊙), remains an open problem, largely because they are so rare that examples of their cold, dense, molecular progenitors continue to be elusive. The molecular cloud G337.342−0.119, the "Pebble," is a candidate cold progenitor. Although G337.342−0.119 was originally identified as four separate ATLASGAL clumps, the similarities in their molecular line velocities and line widths in the MALT90 data set demonstrate that these four clumps are in fact one single, coherent cloud. This cloud is unique in the MALT90 survey for its combination of both cold temperatures (T _dust ~ 14 K) and large line widths (ΔV ~ 10 km s−1). The near/far kinematic distance ambiguity is difficult to resolve for G337.342−0.119. At the near kinematic distance (4.7 kpc), the mass is 5000 M_⊙ and the size is 7 × 2 pc. At the far kinematic distance (11 kpc), the mass is 27,000 M_⊙ and the size is 15 × 4 pc. The unusually large line widths of G337.342−0.119 are difficult to reconcile with a gravitationally bound system in equilibrium. If our current understanding of the Galaxy's Long Bar is approximately correct, G337.342−0.119 cannot be located at its end. Rather, it is associated with a large star-forming complex that contains multiple clumps with large line widths. If G337.342−0.119 is a prototypical cold progenitor for a high-mass cluster, its properties may indicate that the onset of high-mass star cluster formation is dominated by extreme turbulence.]]> Tue 03 Sep 2019 17:58:48 AEST ]]> 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:34953 Tue 03 Sep 2019 17:56:40 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:38094 ⊙ infrared dark molecular filament that exhibits large NH₃ velocity dispersions (σ ~ 8 km s⁻¹) and bright, narrow NH₃(3, 3) line emission. We have probed G23.33-0.30 at the < 0.1 pc scale and confirmed that the narrow NH₃(3, 3) line is emitted by four rare NH₃(3, 3) masers, which are excited by a large-scale shock impacting the filament. G23.33-0.30 also displays a velocity gradient along its length, a velocity discontinuity across its width, shock-tracing SiO(5–4) emission extended throughout the filament, and broad turbulent line widths in NH₃(1, 1) through (6, 6), CS(5–4), and SiO(5–4), as well as an increased NH₃ rotational temperature (T_rot) and velocity dispersion (σ) associated with the shocked, blueshifted component. The correlations among T_rot, σ, and V_LSR imply that the shock is accelerating, heating, and adding turbulent energy to the filament gas. Given G23.33-0.30's location within the giant molecular cloud G23.0-0.4, we speculate that the shock and NH₃(3, 3) masers originated from the supernova remnant (SNR) W41, which exhibits additional evidence of an interaction with G23.0-0.4. We have also detected the 1.3 mm dust continuum emission from at least three embedded molecular cores associated with G23.33-0.30. Although the cores have moderate gas masses (M = 7–10 M_⊙), their large virial parameters (α = 4–9) suggest that they will not collapse to form stars. The turbulent line widths of the (α > 1) cores may indicate negative feedback due to the SNR shock.]]> Tue 03 Aug 2021 18:28:28 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:52118 45 K). The detection rate of the N2D+ emission toward the protostellar cores is 38%, which is higher than 9% for the prestellar cores, indicating that N2D+ does not exclusively trace prestellar cores. The detection rates of the DCO+ emission are 35% for the prestellar cores and 49% for the protostellar cores, which are higher than those for N2D+, implying that DCO+ appears more frequently than N2D+ in both prestellar and protostellar cores. Both the N2D+ and DCO+ abundances appear to decrease from the prestellar to the protostellar stage. The DCN, C2D, and 13CS emission lines are rarely seen in the dense cores of early evolutionary phases. The detection rate of the H2CO emission toward dense cores is 52%, three times higher than that for CH3OH (17%). In addition, the H2CO detection rate, abundance, line intensities, and line widths increase with the core evolutionary status, suggesting that the H2CO line emission is sensitive to protostellar activity.]]> Thu 28 Sep 2023 15:04:02 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:32637 Fri 23 Jun 2023 12:15:31 AEST ]]>