Physical Processes in the Interstellar Medium

Klessen, Ralf S.; Glover, Simon C. O.

doi:10.1007/978-3-662-47890-5_2

Cited by 155 publications

(57 citation statements)

References 738 publications

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“…This is more than 6 orders of magnitude lower than for Sgr A* but comparable to various heating processes operating in the disk of the Milky Way galaxy (Klessen & Glover 2016). We calculate the thermal equilibrium curves at two distances from the centre, i.e.…”

Section: Case Of M60-ucd1mentioning

confidence: 81%

Multiphase environment of compact galactic nuclei: the role of the nuclear star cluster

Różáńska

Kunneriath

Adhikari

et al. 2016

Mon. Not. R. Astron. Soc.

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We study the conditions for the onset of Thermal Instability in the innermost regions of compact galactic nuclei, where the properties of the interstellar environment are governed by the interplay of quasi-spherical accretion onto a supermassive black hole (SMBH) and the heating/cooling processes of gas in a dense nuclear star cluster. Stellar winds are the source of material for radiatively inefficient (quasi-spherical, non-magnetised) inflow/outflow onto the central SMBH, where a stagnation point develops within the Bondi type accretion. We study the local thermal equilibrium to determine the parameter space which allows cold and hot phases in mutual contact to co-exist. We include the effects of mechanical heating by stellar winds and radiative cooling/heating by the ambient field of the dense star cluster. We consider two examples: the Nuclear Star Cluster (NSC) in the Milky Way central region (including the gaseous Mini-spiral of Sgr A*), and the Ultra-Compact Dwarf galaxy M60-UCD1. We find that the two systems behave in different ways because they are placed in different areas of parameter space in the instability diagram: gas temperature vs. dynamical ionization parameter. In the case of Sgr A*, stellar heating prevents the spontaneous formation of cold clouds. The plasma from stellar winds joins the hot X-ray emitting phase and forms an outflow. In M60-UCD1 our model predicts spontaneous formation of cold clouds in the inner part of the galaxy. These cold clouds may survive since the cooling timescale is shorter than the inflow/outflow timescale.

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Section: Case Of M60-ucd1mentioning

confidence: 81%

Multiphase environment of compact galactic nuclei: the role of the nuclear star cluster

Różáńska

Kunneriath

Adhikari

et al. 2016

Mon. Not. R. Astron. Soc.

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“…However, the spectrum decays too quickly at larger l indicating that the corresponding maps exhibit to little small-scale structure. We conclude that the presence of supersonic turbulence, which is ubiquitously observed in the Galactic interstellar medium and which is known to be one of the primary physical agents controlling the star formation process (Elmegreen & Scalo 2004;Mac Low & Klessen 2004;Klessen & Glover 2016), is also important in determining the small-scale characteristics of the Galactic synchrotron emission.…”

Section: Synchrotron Emission and Polarisation Observationsmentioning

confidence: 88%

Radiative Transfer with POLARIS. II. Modeling of Synthetic Galactic Synchrotron Observations

Reißl¹,

Brauer

Klessen

et al. 2019

ApJ

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We present an updated version of POLARIS, a well established code designated for dust polarisation and line radiative transfer (RT) in arbitrary astrophysical environments. We extend the already available capabilities with a synchrotron feature for polarised emission. Here, we combine state-ofthe-art solutions of the synchrotron RT coefficients with numerical methods for solving the complete system of equations of the RT problem, including Faraday rotation (FR) as well as Faraday conversion (FC). We validate the code against Galactic and extragalactic observations by performing a statistical analysis of synthetic all-sky synchrotron maps for positions within the galaxy and for extragalactic observations. For these test scenarios we apply a model of the Milky Way based on sophisticated magneto-hydrodynamic (MHD) simulations and population-synthesis post-processing techniques.We explore different parameters for modeling the distribution of free electrons and for a turbulent magnetic field component. We find that a strongly fluctuating field is necessary for simulating synthetic synchrotron observations on small scales, we argue that Faraday rotation alone can account for the depolarisation of the synchrotron signal, and we discuss the importance of the observer position within the Milky Way. Altogether, we conclude that POLARIS is a highly reliable tool for predicting synchrotron emission and polarisation, including Faraday rotation in a realistic galactic context. It can thus contribute to better understand the results from current and future observational missions.

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“…Schneider et al 2016). At lower densities the molecule is only subthermally excited, at higher densities it becomes quickly optically thick (Draine 2011;Klessen & Glover 2015). The density variation of the associated clumps probably stems from the different optical depths while both isotopes have about the same critical density for the collisional excitation.…”

Section: Discussionmentioning

confidence: 99%

Spatially associated clump populations in Rosette from CO and dust maps

Veltchev

Ossenkopf-Okada

Stanchev

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Spatial association of clumps from different tracers turns out to be a valuable tool to determine the physical properties of molecular clouds. It provides a reliable estimate for the X-factors, serves to trace the density of clumps seen in column densities only and allows to measure the velocity dispersion of clumps identified in dust emission. We study the spatial association between clump populations, extracted by use of the Gaussclumps technique from 12 CO (1 − 0), 13 CO (1 − 0) line maps and Herschel dust-emission maps of the star-forming region Rosette, and analyse their physical properties. All CO clumps that overlap with another CO or dust counterpart are found to be gravitationally bound and located in the massive star-forming filaments of the molecular cloud. They obey a single mass-size relation M cl ∝ R γ cl with γ ≃ 3 (implying constant mean density) and display virtually no velocity-size relation. We interpret their population as low-density structures formed through compression by converging flows and still not evolved under the influence of self-gravity. The high-mass parts of their clump mass functions are fitted by a power law dN cl /d log M cl ∝ M Γ cl and display a nearly Salpeter slope Γ ∼ −1.3. On the other hand, clumps extracted from the dust-emission map exhibit a shallower mass-size relation with γ = 2.5 and mass functions with very steep slopes Γ ∼ −2.3 even if associated with CO clumps. They trace density peaks of the associated CO clumps at scales of a few tenths of pc where no single density scaling law should be expected.

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Physical Processes in the Interstellar Medium

Cited by 155 publications

References 738 publications

Multiphase environment of compact galactic nuclei: the role of the nuclear star cluster

Multiphase environment of compact galactic nuclei: the role of the nuclear star cluster

Radiative Transfer with POLARIS. II. Modeling of Synthetic Galactic Synchrotron Observations

Spatially associated clump populations in Rosette from CO and dust maps

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