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It is widely accepted that supersonic, magnetised turbulence plays a fundamental role for star formation in molecular clouds. It produces the initial dense gas seeds out of which new stars can form. However, the exact relation between gas…

Astrophysics of Galaxies · Physics 2012-04-13 F. Z. Molina , S. C. O. Glover , C. Federrath , R. S. Klessen

The probability density function (PDF) of the gas density in subsonic and supersonic, isothermal, driven turbulence is analyzed with a systematic set of hydrodynamical grid simulations with resolutions up to 1024^3 cells. We performed a…

Solar and Stellar Astrophysics · Physics 2014-11-27 Lukas Konstandin , Philipp Girichidis , Christoph Federrath , Ralf S. Klessen

The density variance - Mach number relation of the turbulent interstellar medium is relevant for theoretical models of the star formation rate, efficiency, and the initial mass function of stars. Here we use high-resolution hydrodynamical…

Astrophysics of Galaxies · Physics 2015-05-08 Christopher A. Nolan , Christoph Federrath , Ralph S. Sutherland

Supersonic turbulence in molecular clouds is a key agent in generating density enhancements that may subsequently go on to form stars. The stronger the turbulence - the higher the Mach number - the more extreme the density fluctuations are…

Astrophysics of Galaxies · Physics 2015-05-18 Chris Brunt

Although there are a wealth of column density tracers for both the molecular and diffuse interstellar medium, there are very few observational studies investigating the relationship between the density variance ($\sigma^2$) and the sonic…

Astrophysics of Galaxies · Physics 2015-06-05 Blakesley Burkhart , A. Lazarian

The density distribution of supersonic isothermal turbulence plays a critical role in many astrophysical systems. It is commonly approximated by a lognormal distribution with a variance of $\sigma_{s,{\rm V}}^2 \approx \ln(1 + b^2 M_{\rm…

Astrophysics of Galaxies · Physics 2026-01-15 Evan Scannapieco , Marcus Brüggen , Philipp Grete , Liubin Pan

We model driven, compressible, isothermal, turbulence with Mach numbers ranging from the subsonic ($\mathcal{M} \approx 0.65$) to the highly supersonic regime ($\mathcal{M}\approx 16 $). The forcing scheme consists both solenoidal…

Solar and Stellar Astrophysics · Physics 2016-06-15 Lukas Konstandin , Wolfram Schmidt , Philipp Girichidis , Thomas Peters , Rahul Shetty , Ralf S. Klessen

Colliding supersonic bulk flows shape observable properties and internal physics of various astrophysical objects, like O-star winds, molecular clouds, galactic sheets, binaries, or gamma-ray bursts. Using numerical simulations, we show…

Solar and Stellar Astrophysics · Physics 2014-01-07 Doris Folini , Rolf Walder , Jean M. Favre

We propose a model for the density statistics in supersonic turbulence, which play a crucial role in star-formation and the physics of the interstellar medium (ISM). Motivated by [Hopkins, MNRAS, 430, 1880 (2013)], the model considers the…

Astrophysics of Galaxies · Physics 2017-08-30 Jonathan Squire , Philip F. Hopkins

In star-forming clouds, high velocity flow gives rise to large fluctuations of density. In this work we explore the correlation between velocity magnitude (speed) and density. We develop an analytic formula for the joint probability…

Astrophysics of Galaxies · Physics 2023-08-02 Branislav Rabatin , David C. Collins

Firstly, we give a historical overview of attempts to incorporate magnetic fields into the Smoothed Particle Hydrodynamics method by solving the equations of Magnetohydrodynamics (MHD), leading an honest assessment of the current…

Astrophysics of Galaxies · Physics 2015-05-20 Daniel J. Price

We study how the estimation of the sonic Mach number ($M_s$) from $^{13}$CO linewidths relates to the actual 3D sonic Mach number. For this purpose we analyze MHD simulations which include post-processing to take radiative transfer effects…

The probability density function (PDF) of the gas density in turbulent supersonic flows is investigated with high-resolution numerical simulations. In a systematic study, we compare the density statistics of compressible turbulence driven…

Astrophysics · Physics 2009-11-13 Christoph Federrath , Ralf S. Klessen , Wolfram Schmidt

Supersonic flows in the interstellar medium (ISM) are believed to be a key driver of the molecular cloud formation and evolution. Among molecular clouds' properties, the ratio between the solenoidal and compressive modes of turbulence plays…

Astrophysics of Galaxies · Physics 2022-05-18 Masato I. N. Kobayashi , Tsuyoshi Inoue , Kengo Tomida , Kazunari Iwasaki , Hiroki Nakatsugawa

Density fluctuations produced by supersonic turbulence are of great importance to astrophysical chemical models. A property of these density fluctuations is that the two point correlation function decreases with increasing scale separation.…

Astrophysics of Galaxies · Physics 2020-09-22 Shmuel Bialy , Blakesley Burkhart

Supersonic turbulence is a key player in controlling the structure and star formation potential of molecular clouds (MCs). The three-dimensional (3D) turbulent Mach number, $\mathcal{M}$, allows us to predict the rate of star formation.…

Astrophysics of Galaxies · Physics 2019-07-17 James R. Beattie , Christoph Federrath , Ralf S. Klessen , Nicola Schneider

[abridged] We determine the relationship between turbulence energy and gas density variance for 15 molecular clouds in the Solar neighbourhood. We use the linewidths of the CO molecule as the probe of the turbulence energy (sonic Mach…

Astrophysics of Galaxies · Physics 2017-12-06 Jouni Kainulainen , Christoph Federrath

This paper investigates the statistical properties of isothermal turbulence in both the subsonic and supersonic regimes. The focus is on the influence of the Mach number ($Ma$) and the Reynolds number ($Re$) on both the space-local and…

Fluid Dynamics · Physics 2025-10-16 F. Thiesset , C. Federrath

Shocks form the basis of our understanding for the density and velocity statistics of supersonic turbulent flows, such as those found in the cool interstellar medium (ISM). The variance of the density field, $\sigma^2_{\rho/\rho_0}$, is of…

Astrophysics of Galaxies · Physics 2021-04-28 James R. Beattie , Philip Mocz , Christoph Federrath , Ralf S. Klessen

We performed numerical simulations of supersonic isothermal turbulence driven by mostly compressive large-scale forcing, using both a static grid and adaptive mesh refinement with an effective resolution N=768^3. After a transient phase…

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