scholarly journals Spatial power spectra of dust across the Local Group: No constraint on disc scale height

2019 ◽  
Vol 492 (2) ◽  
pp. 2663-2682 ◽  
Author(s):  
Eric W Koch ◽  
I-Da Chiang (江宜達) ◽  
Dyas Utomo ◽  
Jérémy Chastenet ◽  
Adam K Leroy ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Power Law ◽  
Large Scale ◽  
Power Spectra ◽  
Far Infrared ◽  
Infrared Emission ◽  
Scale Height ◽  
Turbulent Motion ◽  
Spatial Power Spectrum ◽  
30 Doradus

ABSTRACT We analyse the 1D spatial power spectra of dust surface density and mid to far-infrared emission at $24\!-\!500\, \mu$m in the LMC, SMC, M31, and M33. By forward-modelling the point spread function (PSF) on the power spectrum, we find that nearly all power spectra have a single power-law and point source component. A broken power-law model is only favoured for the LMC 24 μm MIPS power spectrum and is due to intense dust heating in 30 Doradus. We also test for local power spectrum variations by splitting the LMC and SMC maps into 820 pc boxes. We find significant variations in the power-law index with no strong evidence for breaks. The lack of a ubiquitous break suggests that the spatial power spectrum does not constrain the disc scale height. This contradicts claims of a break where the turbulent motion changes from 3D to 2D. The power spectrum indices in the LMC, SMC, and M31 are similar (2.0–2.5). M33 has a flatter power spectrum (1.3), similar to more distant spiral galaxies with a centrally-concentrated H2 distribution. We compare the power spectra of H i, CO, and dust in M31 and M33, and find that H i power spectra are consistently flatter than CO power spectra. These results cast doubt on the idea that the spatial power spectrum traces large scale turbulent motion in nearby galaxies. Instead, we find that the spatial power spectrum is influenced by (1) the PSF on scales below ∼3 times the FWHM, (2) bright compact regions (30 Doradus), and (3) the global morphology of the tracer (an exponential CO disc).

scholarly journals The anisotropy of the power spectrum in periodic cosmological simulations

2021 ◽  
Vol 503 (4) ◽  
pp. 5638-5645
Author(s):  
Gábor Rácz ◽  
István Szapudi ◽  
István Csabai ◽  
László Dobos
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Power Spectra ◽  
Cosmological Simulations ◽  
Spherical Collapse ◽  
Lower Amplitude ◽  
Hydrodynamical Simulations

ABSTRACT The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard Lambda cold dark matter (ΛCDM) initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations is a consequence of the missing large-scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

scholarly journals Anti-symmetric clustering signals in the observed power spectrum

2021 ◽  
Vol 2021 (12) ◽  
pp. 003
Author(s):  
José Fonseca ◽  
Chris Clarkson
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Euler Equation ◽  
Large Scale ◽  
Signal To Noise Ratio ◽  
Power Spectra ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Signal To Noise ◽  
Peculiar Velocities

Abstract In this paper, we study how to directly measure the effect of peculiar velocities in the observed angular power spectra. We do this by constructing a new anti-symmetric estimator of Large Scale Structure using different dark matter tracers. We show that the Doppler term is the major component of our estimator and we show that we can measure it with a signal-to-noise ratio up to ∼ 50 using a futuristic SKAO HI galaxy survey. We demonstrate the utility of this estimator by using it to provide constraints on the Euler equation.

scholarly journals Exact joint likelihood of pseudo-Cℓ estimates from correlated Gaussian cosmological fields

2019 ◽  
Vol 491 (3) ◽  
pp. 3165-3181 ◽  
Author(s):  
Robin E Upham ◽  
Lee Whittaker ◽  
Michael L Brown
Keyword(s):  
Quadratic Form ◽  
Power Spectrum ◽  
Quadratic Forms ◽  
Joint Distribution ◽  
Large Scale ◽  
Power Spectra ◽  
Microwave Background ◽  
Cosmological Constraints ◽  
Statistical Precision ◽  
Joint Likelihood

ABSTRACT We present the exact joint likelihood of pseudo-Cℓ power spectrum estimates measured from an arbitrary number of Gaussian cosmological fields. Our method is applicable to both spin-0 fields and spin-2 fields, including a mixture of the two, and is relevant to cosmic microwave background (CMB), weak lensing, and galaxy clustering analyses. We show that Gaussian cosmological fields are mixed by a mask in such a way that retains their Gaussianity and derive exact expressions for the covariance of the cut-sky spherical harmonic coefficients, the pseudo-aℓms, without making any assumptions about the mask geometry. We then show that each auto or cross-pseudo-Cℓ estimator can be written as a quadratic form, and apply the known joint distribution of quadratic forms to obtain the exact joint likelihood of a set of pseudo-Cℓ estimates in the presence of an arbitrary mask. We show that the same formalism can be applied to obtain the exact joint likelihood of quadratic maximum likelihood power spectrum estimates. Considering the polarization of the CMB as an example, we show using simulations that our likelihood recovers the full, exact multivariate distribution of EE, BB, and EB pseudo-Cℓ power spectra. Our method provides a route to robust cosmological constraints from future CMB and large-scale structure surveys in an era of ever-increasing statistical precision.

scholarly journals Star Formation in the NGC 2071 Molecular Cloud

1989 ◽  
Vol 120 ◽  
pp. 128-128
Author(s):  
N.J. Evans
Keyword(s):  
Star Formation ◽  
High Resolution ◽  
Density Distribution ◽  
Molecular Cloud ◽  
Large Scale ◽  
Far Infrared ◽  
Infrared Emission ◽  
Molecular Outflow ◽  
Broad Array ◽  
Coherent Picture

The NGC 2071 molecular cloud has been studied with a broad array of techniques, including a large scale study of CS emission, high resolution scans in the far-infrared, N H3 studies with the VLA, and near-infrarred imaging. The far-infrared emission constrains the density distribution to fall off approximately as r−1. The NH3 data strongly supports the presence of a disk oriented perpendicular to the molecular outflow, while the CS emission indicates the presence of dense gas in the region. The results will be combined into a coherent picture of this region of current star formation and molecular outflow.

scholarly journals H I Emission and Absorption in the Southern Galactic Plane Survey

2001 ◽  
Vol 18 (1) ◽  
pp. 84-90 ◽  
Author(s):  
N. M. McClure-Griffiths ◽  
John M. Dickey ◽  
B. M. Gaensler ◽  
A. J. Green ◽  
R. F. Haynes ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Radio Telescope ◽  
Large Scale ◽  
Galactic Plane ◽  
Pilot Project ◽  
Small Scale ◽  
Preliminary Results ◽  
Test Region ◽  
Scale Structures ◽  
Spatial Power Spectrum

AbstractWe present preliminary results from the Southern Galactic Plane Survey (SGPS) Test Region and Parkes data. As part of the pilot project for the Southern Galactic Plane Survey, observations of a Test Region (325·5° ≤l ≤ 333·5°; −0·5° ≤ b ≤ 3·5°) were completed in December 1998. Single-dish observations of the full survey region (253° ≤ l ≤ 358 ° |b| ≤ 1°) with the Parkes Radio Telescope were completed in March 2000. We present a sample of SGPS H I data, with particular attention to the smallest-and largest-scale structures seen in absorption and emission, respectively. On the large scale, we detect many prominent H I shells. On the small scale, we note extremely compact, cold clouds seen in H I self-absorption. We explore how these two classes of objects probe opposite ends of the H I spatial power spectrum.

Coherence of Fluctuating Wind Speed and Along-Wind Force Power Spectrum of Tall Building

2014 ◽  
Vol 1025-1026 ◽  
pp. 922-925
Author(s):  
Yong Chul Kim ◽  
Sung Won Yoon
Keyword(s):  
Wind Speed ◽  
Power Spectrum ◽  
Large Scale ◽  
Measurement Data ◽  
Power Spectra ◽  
Tall Building ◽  
Theoretical Formula ◽  
Mathematical Treatment ◽  
Wind Force ◽  
Fluctuating Wind

In evaluating wind load effects on large-scale structures, correlations in the frequency domain (i.e., coherences) and power spectra of fluctuating wind speed should be evaluated in advance. Most existing formulas for coherence are expressed as exponential functions based on field measurement data for ease of mathematical treatment. However, these simple mathematical expressions have many limitations. In the present study, after examining the existing coherence formulas, a semi-theoretical formula was proposed, and the corresponding along-wind force power spectrum of a tall building with a square cross-section was numerically calculated. A comparison showed that both the coherence and along-wind power spectrum were in good agreement with those of actual wind tunnel data.

scholarly journals Interplanetary Scintillation Power Spectra

1976 ◽  
Vol 29 (3) ◽  
pp. 201 ◽  
Author(s):  
RG Milne
Keyword(s):  
Power Spectrum ◽  
Power Law ◽  
Scattering Theory ◽  
Power Spectra ◽  
Inverse Power ◽  
Radio Sources ◽  
Interplanetary Scintillation ◽  
Inverse Power Law ◽  
Power Law Index ◽  
Strong Scattering

Power spectrum measurements of interplanetary scintillation at 408 MHz show that an inverse power law spectrum provides the best description for all scintillating radio sources. The inverse power law index is reasonably constant at ~ 2�4 for solar elongation angles 8 > 10�, and this agrees well with spacecraft observations. For 8 < 10� the index apparently decreases with decreasing 8, and this appears to be consistent with recent strong scattering theory. A Bessel analysis attempted in order to detect Fresnel structure proved unsuccessful because of noise on the power spectra.

An optical study of turbulence

1970 ◽  
Vol 43 (3) ◽  
pp. 607-635 ◽  
Author(s):  
G. E. Roe
Keyword(s):  
Refractive Index ◽  
Power Spectrum ◽  
Power Spectra ◽  
Mean Flow ◽  
Cavendish Laboratory ◽  
Turbulent Region ◽  
Single Beam ◽  
Beam Method ◽  
A New Technique ◽  
Spatial Power Spectrum

This paper describes theoretical and experimental work carried out at the Cavendish Laboratory of the University of Cambridge. The main object of the work was to develop a new technique for measuring the structure of fluid turbulence.A parallel beam of light is passed through the turbulent region, containing refractive index fluctuations, and analyzed on exit by gratings of periodic transmissivity. Two forms of analysis yield (a) the spatial power spectrum of the refractive index fluctuations in the turbulence, and (b) the velocity distribution within the beam aperture. The method does not disturb the fluid physically, does not depend on the existence of a mean flow velocity, and works well in liquids.One of the limitations of this single-beam method is that it produces information averaged along the path length of the beam in the turbulence, and to overcome this a cross-beam technique, using two beams intersecting at right-angles, has been developed in theory. This method gives the spatial power spectrum of the refractive index fluctuations, as does the single beam method, but the results are characteristic only of the volume of intersection of the beams.The paper first discusses the theory of the single-beam and crossed-beam techniques, and then experimental results obtained with the single-beam method.The turbulent region investigated was a rectangular tank of water, heated from below and cooled from above, producing convective turbulence of high Rayleigh number (4·1 × 108), a system difficult to analyze by conventional methods of measurement, such as the hot-wire anemometer.Spectral density functions (power spectra) of refractive index, and hence in this case temperature fluctuations, have been measured, as have velocity distributions. Statistical analysis of the results also gives useful information about the Eulerian time scale of the turbulent field.

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