Polytropic models of filamentary interstellar clouds – I. Structure and stability

Toci, Claudia; Galli, Daniele

doi:10.1093/mnras/stu2168

Cited by 34 publications

(38 citation statements)

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“…A different equation of state or additional physical contribute to the radial stability and can change the morphology of cores. Observed radial density profiles are better matched by polytropic indices lower than one (Toci & Galli 2015). As long as there is a maximum radius in dependence of the linemass we still expect a dichotomy in morphology but with the division not necessarily at half the critical line-mass.…”

Section: Core Morphologymentioning

confidence: 76%

“…Observationally, filaments often show a shallower power law exponent of -1.6 to -2.5 at large radii (Arzoumanian et al 2011;Palmeirim et al 2013). Several processes can explain this difference: truncation of the filament radius in pressure equilibrium (Fischera & Martin 2012), magnetic fields (Fiege & Pudritz 2000), the equation of state (Gehman et al 1996a;Toci & Galli 2015) or filaments formed by shock interaction (Federrath 2016). As the physical reason for the observed profile and how it would impact the radial stability is still unclear, we use the basic isothermal model.…”

Section: Basic Conceptsmentioning

confidence: 99%

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Morphology of prestellar cores in pressure-confined filaments

Heigl

Gritschneder

Burkert

2018

Monthly Notices of the Royal Astronomical Society: Letters

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Observations of prestellar cores in star-forming filaments show two distinct morphologies. While molecular line measurements often show broad cores, submillimeter continuum observations predominantly display pinched cores compared to the bulk of the filament gas. In order to explain how different morphologies arise, we use the gravitational instability model where prestellar cores form by growing density perturbations. The radial extent at each position is set by the local line-mass. We show that the ratio of core radius to filament radius is determined by the initial line-mass of the filament. Additionally, the core morphology is independent of perturbation length scale and inclination, which makes it an ideal diagnostic for observations. Filaments with a line-mass of less than half its critical value should form broad cores, whereas filaments with more than half its critical line-mass value should form pinched cores. For filaments embedded in a constant background pressure, the dominant perturbation growth times significantly differ for low and high line-mass filaments. Therefore, we predict that only one population of cores is present if all filaments within a region begin with similar initial perturbations.

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Section: Core Morphologymentioning

confidence: 76%

Section: Basic Conceptsmentioning

confidence: 99%

Morphology of prestellar cores in pressure-confined filaments

Heigl

Gritschneder

Burkert

2018

Monthly Notices of the Royal Astronomical Society: Letters

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“…The spheroid is not required to be in MHD force balance, but it is expected to be close to self-gravitating equilibrium in at least one dimension, since the Plummer sphere density as a function of spherical radius is similar to that of the isothermal sphere (Bonnor 1966;Ebert 1965). Also, an extended Plummer prolate spheroid has density as a function of cylindrical radius similar to that of a self-gravitating polytropic cylinder (Toci & Galli 2015).…”

Section: This Papermentioning

confidence: 99%

Magnetic Field Structure in Spheroidal Star-forming Clouds

Myers

Basu

Auddy

2018

ApJ

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A model of magnetic field structure is presented to help test the prevalence of flux freezing in star-forming clouds of various shapes, orientations, and degrees of central concentration, and to estimate their magnetic field strength.The model is based on weak-field flux freezing in centrally condensed Plummer spheres and spheroids of oblate and prolate shape. For a spheroid of given density contrast, aspect ratio, and inclination, the model estimates the local field strength and direction, and the global field pattern of hourglass shape. Comparisons with a polarization simulation indicate typical angle agreement within 1 -10 degrees.Scalable analytic expressions are given to match observed polarization patterns, and to provide inputs to radiative transfer codes for more accurate predictions.The model may apply to polarization observations of dense cores, elongated filamentary clouds, and magnetized circumstellar disks. keywords: ISM: clouds¾stars: formation 350 µm showed evidence of the hourglass polarization pattern expected in simple models of flux freezing (Schleuning 1998). Submillimeter observations with the JCMT SCUPOL instrument (Matthews et al. 2009) and with the Planck satellite (Planck Collaboration I. 2016) show highly ordered polarization directions in and around numerous star-forming clouds. The Planck polarization directions agree well with those of near-infrared observations of the same regions. This agreement supports the idea of magnetic grain alignment in star-forming regions, on scales of a few 0.1 pc to a few 10 pc (Soler et al. 2016). At the same time the large-scale structure of nearby star-forming clouds has become available in much greater detail, due to imaging in near-infrared dust extinction by wide-field array cameras (e.g. Lombardi et al. 2006) and due to imaging in far-infrared dust emission by the Herschel satellite (e.g. André et al. 2010). Ordered polarization is seen in the Musca, B211, and L1506 filamentary dark clouds at 1 mm wavelength, where Planck polarization directions lie within 10 deg of perpendicular to the crest direction in the denser Musca and B211 filaments, while they are parallel to the crest direction in the less dense filament L1506 (Planck Collaboration Int. XXXIII 2016). Similarly, polarization directions are observed to be mostly perpendicular to the massive infrared dark cloud filament G11.11-0.12 (Pillai et al. 2016). Recent improvements in the sensitivity and resolution of polarization measurements at far-infrared and submillimeter wavelengths offer new opportunities to relate detailed maps of dust polarization to corresponding maps of dust column density. These include the balloon-borne BLAST-Pol mission (Fissel et al. 2016) and the JCMT BISTRO survey (Pattle et al. 2017), which have made polarization maps of large-scale clouds and filaments. Along with the SAO Submillimeter Array (SMA; Blundell 2007), ALMA (Cox 2016), and SOFIA (Zinnecker et al. 2015) which provide finer angular resolution, these facilities offer an order of magnitude increase in the t...

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“…Finally, we use the new density PDF to determine the SFR in polytropic clouds, given the virial parameter, turbulent driving, Mach number and polytropic Γ. We note that the influence of temperature variations has been explored in previous complementary studies (Vázquez-Semadeni 1994;Passot & Vázquez-Semadeni 1998;Wada & Norman 2001;Kritsuk & Norman 2002;Li et al 2003;Jappsen et al 2005;Audit & Hennebelle 2005, 2010Hennebelle & Audit 2007;Kissmann et al 2008;Seifried et al 2011;Kim et al 2011;Peters et al 2012;Gazol & Kim 2013;Toci & Galli 2015), and we extend these here to much higher resolution and focus on the implications for star formation.…”

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confidence: 99%

The density structure and star formation rate of non-isothermal polytropic turbulence

Federrath

Banerjee²

2015

Monthly Notices of the Royal Astronomical Society

113

128

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The interstellar medium of galaxies is governed by supersonic turbulence, which likely controls the star formation rate (SFR) and the initial mass function (IMF). Interstellar turbulence is non-universal, with a wide range of Mach numbers, magnetic fields strengths, and driving mechanisms. Although some of these parameters were explored, most previous works assumed that the gas is isothermal. However, we know that cold molecular clouds form out of the warm atomic medium, with the gas passing through chemical and thermodynamic phases that are not isothermal. Here we determine the role of temperature variations by modelling non-isothermal turbulence with a polytropic equation of state (EOS), where pressure and temperature are functions of gas density, P ∼ ρ Γ , T ∼ ρ Γ−1 . We use grid resolutions of 2048 3 cells and compare polytropic exponents Γ = 0.7 (soft EOS), Γ = 1 (isothermal EOS), and Γ = 5/3 (stiff EOS). We find a complex network of non-isothermal filaments with more small-scale fragmentation occurring for Γ < 1, while Γ > 1 smoothes out density contrasts. The density probability distribution function (PDF) is significantly affected by temperature variations, with a power-law tail developing at low densities for Γ > 1. In contrast, the PDF becomes closer to a lognormal distribution for Γ 1. We derive and test a new density variance -Mach number relation that takes Γ into account. This new relation is relevant for theoretical models of the SFR and IMF, because it determines the dense gas mass fraction of a cloud, from which stars form. We derive the SFR as a function of Γ and find that it decreases by a factor of ∼ 5 from Γ = 0.7 to Γ = 5/3.

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Polytropic models of filamentary interstellar clouds – I. Structure and stability

Cited by 34 publications

References 56 publications

Morphology of prestellar cores in pressure-confined filaments

Morphology of prestellar cores in pressure-confined filaments

Magnetic Field Structure in Spheroidal Star-forming Clouds

The density structure and star formation rate of non-isothermal polytropic turbulence

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