Examinando por Autor "Barnes, A. T."

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Acceso Abierto
ALMA–IRDC – II. First high-angular resolution measurements of the 14N/15N ratio in a large sample of infrared-dark cloud cores
(Oxford Academics: Oxford University Press, 2021-03-22) Fontani, F.; Barnes, A. T.; Caselli, P.; Henshaw, J. D.; Cosentino, G.; Jimenez-Serra, Izaskun; Tan, J. C.; Pineda, Jaime E.; Law, C. Y.; European Research Council (ERC); Agencia Estatal de Investigación (AEI)
The 14N/15N ratio in molecules exhibits a large variation in star-forming regions, especially when measured from N2H+ isotopologues. However, there are only a few studies performed at high-angular resolution. We present the first interferometric survey of the 14N/15N ratio in N2H+ obtained with Atacama Large Millimeter Array observations towards four infrared-dark clouds harbouring 3 mm continuum cores associated with different physical properties. We detect N15NH+ (1–0) in ∼20−40 per cent of the cores, depending on the host cloud. The 14N/15N values measured towards the millimetre continuum cores range from a minimum of ∼80 up to a maximum of ∼400. The spread of values is narrower than that found in any previous single-dish survey of high-mass star-forming regions and than that obtained using the total power data only. This suggests that the 14N/15N ratio is on average higher in the diffuse gaseous envelope of the cores and stresses the need for high-angular resolution maps to measure correctly the 14N/15N ratio in dense cores embedded in IRDCs. The average 14N/15N ratio of ∼210 is also lower than the interstellar value at the Galactocentric distance of the clouds (∼300–330), although the sensitivity of our observations does not allow us to unveil 14N/15N ratios higher than ∼400. No clear trend is found between the 14N/15N ratio and the core physical properties. We find only a tentative positive trend between 14N/15N and H2 column density. However, firmer conclusions can be drawn only with higher sensitivity measurements.
Acceso Abierto
ALMA–IRDC: dense gas mass distribution from cloud to core scales
(Oxford Academics: Oxford University Press, 2021-03-22) Barnes, A. T.; Henshaw, J. D.; Fontani, F.; Pineda, Jaime E.; Cosentino, G.; Tan, J. C.; Caselli, P.; Wang, K.; Jimenez-Serra, Izaskun; Law, C. Y.; Avison, A.; Bigiel, F.; Feng, S.; Kong, S.; Longmore, Steven N.; Moser, L.; Parker, R. J.; Sánchez Monge, Álvaro ; European Research Council (ERC); Agencia Estatal de Investigación (AEI); Deutsche Forschungsgemeinschaft (DFG); East Asia Core Observatories Association (EACOA); National Natural Science Foundation of China (NSFC); National Key Research and Development Program of China; Peking University; Avison, A. [0000-0002-2562-8609]
Infrared dark clouds (IRDCs) are potential hosts of the elusive early phases of high mass star formation (HMSF). Here, we conduct an in-depth analysis of the fragmentation properties of a sample of 10 IRDCs, which have been highlighted as some of the best candidates to study HMSF within the Milky Way. To do so, we have obtained a set of large mosaics covering these IRDCs with Atacama Large Millimeter/submillimeter Array (ALMA) at Band 3 (or 3 mm). These observations have a high angular resolution (∼3 arcsec; ∼0.05 pc), and high continuum and spectral line sensitivity (∼0.15 mJy beam−1 and ∼0.2 K per 0.1 km s−1 channel at the N2H+ (1 − 0) transition). From the dust continuum emission, we identify 96 cores ranging from low to high mass (M = 3.4−50.9 M⊙) that are gravitationally bound (αvir = 0.3−1.3) and which would require magnetic field strengths of B = 0.3−1.0 mG to be in virial equilibrium. We combine these results with a homogenized catalogue of literature cores to recover the hierarchical structure within these clouds over four orders of magnitude in spatial scale (0.01–10 pc). Using supplementary observations at an even higher angular resolution, we find that the smallest fragments (<0.02 pc) within this hierarchy do not currently have the mass and/or the density required to form high-mass stars. None the less, the new ALMA observations presented in this paper have facilitated the identification of 19 (6 quiescent and 13 star-forming) cores that retain >16 M⊙ without further fragmentation. These high-mass cores contain trans-sonic non-thermal motions, are kinematically sub-virial, and require moderate magnetic field strengths for support against collapse. The identification of these potential sites of HMSF represents a key step in allowing us to test the predictions from high-mass star and cluster formation theories.
Acceso Abierto
Magnetic field morphology and evolution in the Central Molecular Zone and its effect on gas dynamics
(EDP Sciences, 2024-11-22) Tress, Robin; Sormani, Mattia Carlo; Girichidis, P.; Glover, Simon; Klessen, Ralf Stephan; Smith, Rowan; Sobacchi, E.; Armillotta, Lucia; Barnes, A. T.; Battersby, C.; Bogue, Kamran R. J.; Brucy, Noé; Colzi, Laura; Federrath, C.; García, Pablo; Ginsburg, A.; Göller, Junia Aletta Beatrix; Hatchfield, H. P.; Henkel, C.; Hennebelle, P.; Henshaw, J. D.; Hirschmann, M.; Hu, Y.; Kauffmann, J.; Kruijssen, J. M. D.; Lazarian, A.; Lipman, Dani R.; Longmore, S. N.; Morris, Mark; Nogueras Lara, Francisco; Petkova, Maya A.; Pillai, Thushara; Rivilla, Victor M.; Sánchez Monge, Álvaro; Soler, Juan Diego; Whitworth, David; Zhang, Qizhou; European Research Council (ERC); Royal Society; National Science Foundation (NSF); Consejo Superior de Investigaciones Científicas (CSIC); European Commission (EC); Deutsche Forschungsgemeinschaft (DFG); Ministerio de Ciencia e Innovación (MICINN); Agencia Estatal de Investigación (AEI); Chinese Academy of Science (CAS); Consejo Nacional de Ciencia y Tecnología (CONACyT); Unidad de Excelencia Científica María de Maeztu INSTITUTO DE CIENCIAS DEL ESPACIO, CEX2020-001058-M
The interstellar medium in the Milky Way’s Central Molecular Zone (CMZ) is known to be strongly magnetised, but its large-scale morphology and impact on the gas dynamics are not well understood. We explore the impact and properties of magnetic fields in the CMZ using three-dimensional non-self gravitating magnetohydrodynamical simulations of gas flow in an external Milky Way barred potential. We find that: (1) The magnetic field is conveniently decomposed into a regular time-averaged component and an irregular turbulent component. The regular component aligns well with the velocity vectors of the gas everywhere, including within the bar lanes. (2) The field geometry transitions from parallel to the Galactic plane near ɀ = 0 to poloidal away from the plane. (3) The magneto-rotational instability (MRI) causes an in-plane inflow of matter from the CMZ gas ring towards the central few parsecs of 0.01−0.1 M⊙ yr−1 that is absent in the unmagnetised simulations. However, the magnetic fields have no significant effect on the larger-scale bar-driven inflow that brings the gas from the Galactic disc into the CMZ. (4) A combination of bar inflow and MRI-driven turbulence can sustain a turbulent vertical velocity dispersion of σɀ = 5 km s−1 on scales of 20 pc in the CMZ ring. The MRI alone sustains a velocity dispersion of σɀ ≃ 3 km s−1. Both these numbers are lower than the observed velocity dispersion of gas in the CMZ, suggesting that other processes such as stellar feedback are necessary to explain the observations. (5) Dynamo action driven by differential rotation and the MRI amplifies the magnetic fields in the CMZ ring until they saturate at a value that scales with the average local density as B ≃ 102 (n/103 cm−3)0.33 µG. Finally, we discuss the implications of our results within the observational context in the CMZ.
Acceso Abierto
SiO emission as a probe of cloud–cloud collisions in infrared dark clouds
(Oxford Academics: Oxford University Press, 2020-09-25) Cosentino, R.; Jiménez Serra, I.; Henshaw, J. D.; Caselli, P.; Viti, S.; Barnes, A. T.; Tan, T. C.; Fontani, F.; Wu, B.; European Research Council (ERC); Ministerio de Economía y Competitividad (MINECO); Henshaw, J. [0000-0001-9656-7682]; Fontani, F. [0000-0003-0348-3418]; Barnes, A. [0000-0003-0410-4504]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Infrared dark clouds (IRDCs) are very dense and highly extincted regions that host the initial conditions of star and stellar cluster formation. It is crucial to study the kinematics and molecular content of IRDCs to test their formation mechanism and ultimately characterize these initial conditions. We have obtained high-sensitivity Silicon Monoxide, SiO(2–1), emission maps towards the six IRDCs, G018.82–00.28, G019.27+00.07, G028.53–00.25, G028.67+00.13, G038.95–00.47, and G053.11+00.05 (cloud A, B, D, E, I, and J, respectively), using the 30-m antenna at the Instituto de Radioastronomía Millimétrica (IRAM30m). We have investigated the SiO spatial distribution and kinematic structure across the six clouds to look for signatures of cloud–cloud collision events that may have formed the IRDCs and triggered star formation within them. Towards clouds A, B, D, I, and J, we detect spatially compact SiO emission with broad-line profiles that are spatially coincident with massive cores. Towards the IRDCs A and I, we report an additional SiO component that shows narrow-line profiles and that is widespread across quiescent regions. Finally, we do not detect any significant SiO emission towards cloud E. We suggest that the broad and compact SiO emission detected towards the clouds is likely associated with ongoing star formation activity within the IRDCs. However, the additional narrow and widespread SiO emission detected towards cloud A and I may have originated from the collision between the IRDCs and flows of molecular gas pushed towards the clouds by nearby H II regions.