Histogram of oriented gradients: a technique for the study of molecular cloud formation

Abstract

We introduce the histogram of oriented gradients (HOG), a tool developed for machine vision that we propose as a new metric for the systematic characterization of observations of atomic and molecular gas and the study of molecular cloud formation models. In essence, the HOG technique takes as input extended spectral-line observations from two tracers and provides an estimate of their spatial correlation across velocity channels. We characterize HOG using synthetic observations of HI and ${}^{13}$CO(J=1-0) emission from numerical simulations of MHD turbulence leading to the formation of molecular gas after the collision of two atomic clouds. We find a significant spatial correlation between the two tracers in velocity channels where $v_{HI}\approx v_{{}^{13}CO}$, independent of the orientation of the collision with respect to the line of sight. We use HOG to investigate the spatial correlation of the HI, from the THOR survey, and the ${}^{13}$CO(J=1-0) emission, from the GRS, toward the portion of the Galactic plane 33.75$<l<$35.25${}^o$ and $|b|<$1.25${}^o$. We find a significant spatial correlation between the tracers in extended portions of the studied region. Although some of the regions with high spatial correlation are associated with HI self-absorption features, suggesting that it is produced by the cold atomic gas, the correlation is not exclusive to this kind of region. The HOG results also indicate significant differences between individual regions: some show spatial correlation in channels around $v_{HI}\approx v_{{}^{13}CO}$ while others present this correlation in velocity channels separated by a few km/s. We associate these velocity offsets to the effect of feedback and to the presence of physical conditions that are not included in the atomic-cloud-collision simulations, such as more general magnetic field configurations, shear, and global gas infall.

arXiv comment32 pages, 36 figures. Accepted for publication at A&A (28DEC2018)

References in corpus (65)

• Astropy: A Community Python Package for Astronomy
• E pur si muove: Galiliean-invariant cosmological hydrodynamical simulations on a moving mesh
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• The Interstellar Environment of our Galaxy
• Cold Dark Clouds: The Initial Conditions for Star Formation
• Structure of Stationary Photodissociation Fronts
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of the Warm and Cold Neutral Media
• Rapid Formation of Molecular Clouds and Stars in the Solar Neighborhood
• The Atomic to Molecular Transition in Galaxies. II: HI and H_2 Column Densities
• Radiative torques: Analytical Model and Basic Properties
• Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds
• The VLA Galactic Plane Survey
• The WISE Catalog of Galactic HII Regions
• Velocity Modification of HI Power Spectrum
• Physical properties of molecular clouds for the entire Milky Way disk
• Turbulent molecular clouds
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• The Red MSX Source Survey: the Massive Young Stellar Population of our Galaxy
• An Imprint of Molecular Cloud Magnetization in the Morphology of the Dust Polarized Emission
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• A Spitzer Space Telescope Infrared Survey of Supernova Remnants in the Inner Galaxy
• Modeling UV Radiation Feedback from Massive Stars: II. Dispersal of Star-Forming Giant Molecular Clouds by Photoionization and Radiation Pressure
• Molecular gas kinematics within the central 250 pc of the Milky Way
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• The Atomic to Molecular Transition in Galaxies. I: An Analytic Approximation for Photodissociation Fronts in Finite Clouds
• The Birth of Molecular Clouds: Formation of Atomic Precursors in Colliding Flows
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• Modeling the Warm Ionized Interstellar Medium and Its Impact on Elemental Abundance Studies
• TreeCol: a novel approach to estimating column densities in astrophysical simulations
• HI Narrow Line Absorption in Dark Clouds
• Giant Molecular Filaments in the Milky Way
• HI Narrow Self-Absorption in Dark Clouds: Correlations with Molecular Gas and Implications for Cloud Evolution and Star Formation
• The Spin Temperature of Warm Interstellar H I
• Winds and radiation in unison: a new semi-analytic feedback model for cloud dissolution
• A Magnetically-Supported Photodissociation Region in M17
• Tracing magnetic fields with spectroscopic channel maps
• What are we learning from the relative orientation between density structures and the magnetic field in molecular clouds?
• Quantifying Observational Projection Effects Using Molecular Cloud Simulations
• Galactic Supernova Remnant Candidates Discovered by THOR
• On the relation between the column density structures and the magnetic field orientation in the Vela C molecular complex
• On the structure of the turbulent interstellar atomic hydrogen. I- Physical characteristics
• Molecular clouds and clumps in the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• Modelling [CI] emission from turbulent molecular clouds
• Distribution and mass of diffuse and dense CO gas in the Milky Way
• Fitting Together the HI Absorption and Emission in the SGPS
• A Self-Absorption Census of Cold HI Clouds in the Canadian Galactic Plane Survey
• The structure of the thermally bistable and turbulent atomic gas in the local interstellar medium
• An application of an optimal statistic for characterising relative orientations
• Supergiant Shells and Molecular Cloud Formation in the LMC
• The ${}^{12}$CO/${}^{13}$CO ratio in turbulent molecular clouds
• The formation of the W43 complex: constraining its atomic-to-molecular transition and searching for colliding clouds
• Cold and warm atomic gas around the Perseus molecular cloud I: Basic Properties
• Interpreting the Star Formation Efficiency of Molecular Clouds with Ionising Feedback
• Three Dimensional Hydrodynamic Simulations of Multiphase Galactic Disks with Star Formation Feedback: II. Synthetic HI 21 cm Line Observations
• UV-driven chemistry in simulations of the interstellar medium. I. Post-processed chemistry with the Meudon PDR code
• The HI/OH/Recombination line survey of the inner Milky Way (THOR)
• Continuum sources from the THOR survey between 1 and 2 GHz
• The FRIGG project: From intermediate galactic scales to self-gravitating cores
• "Missing Link" Clouds in the Southern Galactic Plane Survey
• An Improved Technique for Measurement of Cold HI in Molecular Cloud Cores
• Gas Kinematics and Star Formation in the Filamentary IRDC G34.43+0.24
• A Neutral Hydrogen Self-Absorption Cloud in the SGPS
• Feedback in W49A diagnosed with radio recombination lines and models
• Physical properties of a very diffuse HI structure at high Galactic latitude

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• Galaxy Morphological Classification Catalogue of the Dark Energy Survey Year 3 data with Convolutional Neural Networks
• The history of dynamics and stellar feedback revealed by the HI filamentary structure in the disk of the Milky Way
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• Velocity Gradient in the Presence of Self-Gravity: Identifying Gravity-induced Inflow and Determining Collapsing Stage
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• Probing Magnetic Field Morphology in Galaxy Clusters with the Gradient Technique
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• Automated Lensing Learner: Automated Strong Lensing Identification with a Computer Vision Technique
• Physical and chemical complexity in high-mass star-forming regions with ALMA. I. Overview and evolutionary trends of physical properties
• Relative Alignment between Dense Molecular Cores and Ambient Magnetic Field: The Synergy of Numerical Models and Observations
• Atomic and molecular gas properties during cloud formation
• Clustered star formation at early evolutionary stages. Physical and chemical analysis of the young star-forming regions ISOSS J22478+6357 and ISOSS J23053+5953
• Comment on Clark et al. (2019) "The Physical Nature of Neutral Hydrogen Intensity Structure"
• A panoptic view of the Taurus molecular cloud I. The cloud dynamics revealed by gas emission and 3D dust
• First look at the multiphase interstellar medium with synthetic observations of low-frequency Faraday tomography
• Kinetic tomography of the Galactic plane within 1.25 kiloparsecs from the Sun. The interstellar flows revealed by HI and CO line emission and 3D dust
• Intermittency of Fast MHD Modes and Regions of Anomalous Gradient Orientation in Low-beta Plasmas
• The filamentary structures in the CO emission toward the Milky Way disk
• Application of Convolutional Neural Networks to Predict Magnetic Fields Directions in Turbulent Clouds
• The Kinematic Structure of Magnetically Aligned HI Filaments
• ALMAGAL IV. Morphological comparison of molecular and thermal dust emission using the histogram of oriented gradients (HOG) method
• Neutral hydrogen filaments in interstellar media: Are they physical?
• On the Flux-Intensity Relation of Molecular Clouds
• A three-dimensional model for the reversal in the local large-scale interstellar magnetic field
• Cold atomic gas identified by HI self-absorption. Cold atomic clouds toward giant molecular filaments
• Directional data analysis using the spherical Cauchy and the Poisson kernel-based distribution
• Image Segmentation, Compression and Reconstruction from Edge Distribution Estimation with Random Field and Random Cluster Theories
• The contribution of neutral gas to Faraday tomographic data at low frequencies. A first extensive comparison between real and synthetic data