| 1. |
- Soler, J. D., et al.
(författare)
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Histogram of oriented gradients: a technique for the study of molecular cloud formation
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 622
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Tidskriftsartikel (refereegranskat)abstract
- We introduce the histogram of oriented gradients (HOG), a tool developed for machine vision that we propose as a new metric for the systematic characterization of spectral line observations of atomic and molecular gas and the study of molecular cloud formation models. In essence, the HOG technique takes as input extended spectral-line observations from two tracers and provides an estimate of their spatial correlation across velocity channels. We characterized HOG using synthetic observations of HI and (CO)-C-13(J = 1 -> 0) emission from numerical simulations of magnetohydrodynamic (MHD) turbulence leading to the formation of molecular gas after the collision of two atomic clouds. We found a significant spatial correlation between the two tracers in velocity channels where v(HI) approximate to v(13CO), almost independent of the orientation of the collision with respect to the line of sight. Subsequently, we used HOG to investigate the spatial correlation of the HI, from The HI/OH/recombination line survey of the inner Milky Way (THOR), and the (CO)-C-13(J = 1 -> 0) emission from the Galactic Ring Survey (GRS), toward the portion of the Galactic plane 33.degrees 75 <= l <= 35.degrees 25 and vertical bar b vertical bar <= 1.degrees 25. We found a significant spatial correlation between the two tracers in extended portions of the studied region. Although some of the regions with high spatial correlation are associated with HI self-absorption (HISA) features, suggesting that it is produced by the cold atomic gas, the correlation is not exclusive to this kind of region. The HOG results derived for the observational data indicate significant differences between individual regions: some show spatial correlation in channels around v(HI) approximate to v(13CO) while others present spatial correlations in velocity channels separated by a few kilometers per second. We associate these velocity offsets to the effect of feedback and to the presence of physical conditions that are not included in the atomic-cloud-collision simulations, such as more general magnetic field configurations, shear, and global gas infall.
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| 2. |
- Treviño Morales, Sandra, 1985, et al.
(författare)
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Dynamics of cluster-forming hub-filament systems The case of the high-mass star-forming complex Monoceros R2
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 629
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Tidskriftsartikel (refereegranskat)abstract
- Context. High-mass stars and star clusters commonly form within hub-filament systems. Monoceros R2 (hereafter Mon R2), at a distance of 830 pc, harbors one of the closest of these systems, making it an excellent target for case studies. Aims. We investigate the morphology, stability and dynamical properties of the Mon R2 hub-filament system. Methods. We employed observations of the (CO)-C-13 and (CO)-O-18 1 -> 0 and 2 -> 1 lines obtained with the IRAM-30m telescope. We also used H-2 column density maps derived from Herschel dust emission observations. Results. We identified the filamentary network in Mon R-2 with the DisPerSE algorithm and characterized the individual filaments as either main (converging into the hub) or secondary (converging to a main filament). The main filaments have line masses of 30-100 M-circle dot pc(-1) and show signs of fragmentation, while the secondary filaments have line masses of 12-60 M-circle dot pc(-1) and show fragmentation only sporadically. In the context of Ostriker's hydrostatic filament model, the main filaments are thermally supercritical. If non-thermal motions are included, most of them are transcritical. Most of the secondary filaments are roughly transcritical regardless of whether non-thermal motions are included or not. From the morphology and kinematics of the main filaments, we estimate a mass accretion rate of 10(-4)-10(-3) M-circle dot yr(-1) into the central hub. The secondary filaments accrete into the main filaments at a rate of 0.1-0.4 x 10(-4) M-circle dot yr(-1). The main filaments extend into the central hub. Their velocity gradients increase toward the hub, suggesting acceleration of the gas. We estimate that with the observed infall velocity, the mass-doubling time of the hub is similar to 2.5 Myr, ten times longer than the free-fall time, suggesting a dynamically old region. These timescales are comparable with the chemical age of the HII region. Inside the hub, the main filaments show a ring-or a spiral-like morphology that exhibits rotation and infall motions. One possible explanation for the morphology is that gas is falling into the central cluster following a spiral-like pattern.
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| 3. |
- André, Ph., et al.
(författare)
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Probing the cold magnetised Universe with SPICA-POL (B-BOP)
- 2019
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Ingår i: Publications Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 36
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Forskningsöversikt (refereegranskat)abstract
- Space Infrared Telescope for Cosmology and Astrophysics (SPICA), the cryogenic infrared space telescope recently pre-selected for a 'Phase A' concept study as one of the three remaining candidates for European Space Agency (ESA's) fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager [SPICA-POL, now called B-fields with BOlometers and Polarizers (B-BOP)], which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetised Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100-350 mu m images of linearly polarised dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 mu m images will also have a factor similar to 30 higher resolution than Planck polarisation data. This will make B-BOP a unique tool for characterising the statistical properties of the magnetised ISM and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing Galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.
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