On the Effects of Projection on Morphology

Abstract

We study the effects of projection of three-dimensional (3D) data onto the plane of the sky by means of numerical simulations of turbulence in the interstellar medium including the magnetic field, parameterized cooling and diffuse and stellar heating, self-gravity and rotation. We compare the physical-space density and velocity distributions with their representation in position-position-velocity (PPV) space (``channel maps''), noting that the latter can be interpreted in two ways: either as maps of the column density's spatial distribution (at a given line-of-sight (LOS) velocity), or as maps of the spatial distribution of a given value of the LOS velocity (weighted by density). This ambivalence appears related to the fact that the spatial and PPV representations of the data give significantly different views. First, the morphology in the channel maps more closely resembles that of the spatial distribution of the LOS velocity component than that of the density field, as measured by pixel-to-pixel correlations between images. Second, the channel maps contain more small-scale structure than 3D slices of the density and velocity fields, a fact evident both in subjective appearance and in the power spectra of the images. This effect may be due to a pseudo-random sampling (along the LOS) of the gas contributing to the structure in a channel map: the positions sampled along the LOS (chosen by their LOS velocity) may vary significantly from one position in the channel map to the next.

6 figures. To appear in the March 20th volume in ApJ

References in corpus (10)

• Kinetic Energy Decay Rates of Supersonic and Super-Alfvenic Turbulence in Star-Forming Clouds
• Velocity Modification of HI Power Spectrum
• A Super-Alfvenic Model of Dark Clouds
• Supersonic turbulence in the ISM: stellar extinction determinations as probes of the structure and dynamics of dark clouds
• Kinetic and Structural Evolution of Self-gravitating, Magnetized Clouds: 2.5-Dimensional Simulations of Decaying Turbulence
• A Turbulent Model for the Interstellar Medium. II. Magnetic Fields and Rotation
• Can Nonlinear Hydromagnetic Waves Support a Self-Gravitating Cloud?
• TURBULENCE IN MOLECULAR CLOUDS
• The Spectral Correlation Function -- A New Tool for Analyzing Spectral-Line Maps
• Synthetic Molecular Clouds from Supersonic MHD and Non-LTE Radiative Transfer Calculations

Cited by in corpus (32)

• Theory of Star Formation
• Interstellar Turbulence I: Observations and Processes
• Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models
• Star Formation from Galaxies to Globules
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• Physical vs. Observational Properties of Clouds in Turbulent Molecular Cloud Models
• A Fractal Analysis of the HI Emission from the Large Magellanic Cloud
• The linewidth-size relationship in the dense ISM of the Central Molecular Zone
• A Fractal Origin for the Mass Spectrum of Interstellar Clouds: II. Cloud Models and Power Law Slopes
• Analysis of Clumps in Molecular Cloud Models: Mass Spectrum, Shapes, Alignment and Rotation
• Fractal Structure in Galactic Star Fields
• Quantifying Observational Projection Effects Using Molecular Cloud Simulations
• Maximally Star-Forming Galactic Disks II. Vertically-Resolved Hydrodynamic Simulations of Starburst Regulation
• A Turbulent Origin for Flocculent Spiral Structure in Galaxies
• Turbulence driven by outflow-blown cavities in the molecular cloud of NGC 1333
• The Effect of Projection on Derived Mass-Size and Linewidth-Size Relationships
• The Angular Momentum of Magnetized Molecular Cloud Cores: A 2D-3D Comparison
• Line Profiles of Cores within Clusters: I. The Anatomy of a Filament
• The Physical Nature of Neutral Hydrogen Intensity Structure
• Emissivity Statistics in Turbulent, Compressible MHD Flows and the Density-Velocity Correlation
• Velocity statistics from spectral line data: effects of density-velocity correlations, magnetic field, and shear
• Hierarchical Structure of Magnetohydrodynamic Turbulence In Position-Position-Velocity Space
• The Spectral Correlation Function of Molecular Clouds: A Statistical Test for Theoretical Models
• Hydrodynamical simulations of the decay of high-speed molecular turbulence. II. Divergence from isothermality
• Rethinking the N(H2)/I(CO) Conversion Factor
• Molecular cloud formation as seen in synthetic Hi and molecular gas observations
• G-virial: Gravity-based structure analysis of molecular clouds
• Velocity Structure of the ISM as Seen by the Spectral Correlation Function
• Effects of Galactic Disc Inclination and Resolution on Observed GMC Properties and Larson's Scaling Relations
• Dependence of Molecular Cloud Samples on Angular Resolution, Sensitivity, and Algorithms
• The VMC survey -- XLVII. Turbulence-Controlled Hierarchical Star Formation in the Large Magellanic Cloud
• Connecting the Cosmic Star Formation Rate with the Local Star Formation