The Phase Coherence of Interstellar Density Fluctuations

Burkhart, Blakesley; Lazarían, A.

doi:10.3847/0004-637x/827/1/26

Cited by 18 publications

(16 citation statements)

References 46 publications

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“…The spatial power spectrum, defined as the Fourier transform of the two-point autocorrelation function, does not include information about phase. Burkhart et al (2009) introduced the bispectrum as a tool for probing nonlinear wave-wave interactions in a turbulent energy cascade (see also Burkhart & Lazarian 2016). They showed that MHD wave modes produce stronger turbulence correlations than that of purely hydrodynamical perturbations.…”

Section: Bispectrum/bicoherencementioning

confidence: 99%

Assessing the Impact of Astrochemistry on Molecular Cloud Turbulence Statistics

Boyden

Offner

Koch

et al. 2018

ApJ

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We analyze hydrodynamic simulations of turbulent, star-forming molecular clouds that are post-processed with the photo-dissociation region astrochemistry code 3D-PDR. We investigate the sensitivity of 15 commonly applied turbulence statistics to post-processing assumptions, namely variations in gas temperature, abundance and external radiation field. We produce synthetic 12 CO(1-0) and CI( 3 P 1 -3 P 0 ) observations and examine how the variations influence the resulting emission distributions. To characterize differences between the datasets, we perform statistical measurements, identify diagnostics sensitive to our chemistry parameters, and quantify the statistic responses by using a variety of distance metrics. We find that multiple turbulent statistics are sensitive not only to the chemical complexity but also to the strength of the background radiation field. The statistics with meaningful responses include principal component analysis, spatial power spectrum and bicoherence. A few of the statistics, such as the velocity coordinate spectrum, are primarily sensitive to the type of tracer being utilized, while others, like the ∆-variance, strongly respond to the background radiation field. Collectively, these findings indicate that more realistic chemistry impacts the responses of turbulent statistics and is necessary for accurate statistical comparisons between models and observed molecular clouds.

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Section: Bispectrum/bicoherencementioning

confidence: 99%

Assessing the Impact of Astrochemistry on Molecular Cloud Turbulence Statistics

Boyden

Offner

Koch

et al. 2018

ApJ

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“…The 3PCF has had significant success in cosmology describing the non-Gaussian distribution of galaxies (Slepian et al (2017a,b), and references therein). The 3PCF (Portillo et al 2018) and bispectrum (Burkhart et al 2009;Burkhart & Lazarian 2016) have also been applied to MHD simulations and show some discriminatory power, but interpretation of these higher order statistics remains difficult.…”

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confidence: 99%

Classification of Magnetohydrodynamic Simulations using Wavelet Scattering Transforms

Saydjari,

Portillo,

Slepian

et al. 2020

Preprint

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The complex interplay of magnetohydrodynamics, gravity, and supersonic turbulence in the interstellar medium (ISM) introduces non-Gaussian structure that can complicate comparison between theory and observation. We show that the Wavelet Scattering Transform (WST), in combination with linear discriminant analysis (LDA), is sensitive to non-Gaussian structure in 2D ISM dust maps. WST-LDA classifies magnetohydrodynamic (MHD) turbulence simulations with up to a 97% true positive rate in our testbed of 8 simulations with varying sonic and Alfvénic Mach numbers. We present a sideby-side comparison with two other methods for non-Gaussian characterization, the Reduced Wavelet Scattering Transform (RWST) and the 3-Point Correlation Function (3PCF). We also demonstrate the 3D-WST-LDA and apply it to classification of density fields in position-position-velocity (PPV) space, where density correlations can be studied using velocity coherence as a proxy. WST-LDA is robust to common observational artifacts, such as striping and missing data, while also sensitive enough to extract the net magnetic field direction for sub-Alfvénic turbulent density fields. We include a brief analysis of the effect of point spread functions and image pixelization on 2D-WST-LDA applied to density fields, which informs the future goal of applying WST-LDA to 2D or 3D all-sky dust maps to extract hydrodynamic parameters of interest.

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“…For example,Burkhart & Lazarian (2016), analysing numerical simulations of isothermal Scheme of descriptors used to quantitatively characterize the MFS in this work, and introduced in the text. The example MFS (green curve) is the one of the 224 map at 250 µm, also contained inFigure 5.…”

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confidence: 99%

Multifractal analysis of the interstellar medium: first application to Hi-GAL observations

Elia

Strafella

Dib

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The multifractal geometry remains an under-exploited approach to describe and quantify the large-scale structure of interstellar clouds. In this paper, the typical tools of multifractal analysis are applied to Herschel far-infrared (70-500 µm) dust continuum maps, which represent an ideal case of study. This dust component is a relatively optically thin tracer at these wavelengths and the size in pixel of the maps is well suitable for this statistical analysis. We investigate the so-called multifractal spectrum and generalised fractal dimension of six Hi-GAL regions in the third Galactic quadrant. We measure systematic variations of the spectrum at increasing wavelength, which generally correspond to an increasing complexity of the image, and we observe peculiar behaviours of the investigated fields, strictly related to the presence of highemission regions, which in turn are connected to star formation activity. The same analysis is applied to synthetic column density maps, generated from numerical turbulent molecular cloud models and from fractal Brownian motion (fBm), allowing for the confrontation of the observations with models with well controlled physical parameters. This comparison shows that, in terms of multifractal descriptors of the structure, fBm images exhibit a very different, quite unrealistic behaviour when compared with Hi-GAL observations, whereas the numerical simulations appear in some cases (depending on the specific model) more similar to the observations. Finally, the link between mono-fractal parameters (commonly found in the literature) and multifractal indicators is investigated: the former appear to be only partially connected with the latter, with the multifractal analysis offering a more extended and complete characterization of the cloud structure.

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The Phase Coherence of Interstellar Density Fluctuations

Cited by 18 publications

References 46 publications

Assessing the Impact of Astrochemistry on Molecular Cloud Turbulence Statistics

Assessing the Impact of Astrochemistry on Molecular Cloud Turbulence Statistics

Classification of Magnetohydrodynamic Simulations using Wavelet Scattering Transforms

Multifractal analysis of the interstellar medium: first application to Hi-GAL observations

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