Probing the cold neutral medium through HI emission morphology with the scattering transform

Abstract

Neutral hydrogen (HI) emission exhibits complex morphology that encodes rich information about the physics of the interstellar medium (ISM). We apply the scattering transform (ST) to characterize HI emission structure via a set of compact and interpretable coefficients, and find a connection between HI emission morphology and HI cold neutral medium (CNM) phase content. Where HI absorption measurements are unavailable, the HI phase structure is typically estimated from the emission via spectral line decomposition. Here we present the first probe of CNM content using measures solely derived from HI emission spatial information. We apply the scattering transform to GALFA-HI data at high Galactic latitudes (|b|>30 deg), and compare the resulting coefficients to CNM fraction measurements derived from archival HI emission and absorption spectra. We quantify the correlation between the ST coefficients and measured CNM fraction (fCNM), and find that HI emission morphology encodes substantial fCNM-correlating information, and that ST-based metrics for small-scale linearity are particularly predictive of fCNM. This is further corroborated by the enhancement of $I_{857}/N_{HI}$ ratio with larger ST measures of small-scale linearity. These results are consistent with the picture that regions with higher CNM content are more populated with small-scale filamentary HI structures. Our work illustrates a physical connection between HI morphology and phase content, and suggests that future phase decomposition methods can be improved by making use of both HI spectral and spatial information.

References in corpus (33)

• The NumPy array: a structure for efficient numerical computation
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• A new, large-scale map of interstellar reddening derived from HI emission
• Dust variations in the diffuse interstellar medium: constraints on Milky Way dust from Planck-HFI observations
• Mapping the Magnetic Interstellar Medium in Three Dimensions Over the Full Sky with Neutral Hydrogen
• Magnetically Dominated Strands of Cold Hydrogen in the Riegel-Crutcher Cloud
• The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results
• The Physical Nature of Neutral Hydrogen Intensity Structure
• ROHSA: Regularized Optimization for Hyper-Spectral Analysis - Application to phase separation of 21 cm data
• Going Beyond the Galaxy Power Spectrum: an Analysis of BOSS Data with Wavelet Scattering Transforms
• Cold gas in the Milky Way's nuclear wind
• Three Dimensional Hydrodynamic Simulations of Multiphase Galactic Disks with Star Formation Feedback: II. Synthetic HI 21 cm Line Observations
• Formation of HI Clouds in Shock-compressed Interstellar Medium: Physical Origin of Angular Correlation Between Filamentary Structure and Magnetic Field
• Gaussian decomposition of HI surveys. III. Local HI
• Classification of Magnetohydrodynamic Simulations using Wavelet Scattering Transforms
• Statistical description of dust polarized emission from the diffuse interstellar medium -- A RWST approach
• HI filaments are cold and associated with dark molecular gas. HI4PI based estimates of the local diffuse CO-dark H2 distribution
• The Galactic dynamics revealed by the filamentary structure in atomic hydrogen emission
• Extracting the cold neutral medium from HI emission with deep learning: Implications for Galactic foregrounds at high latitude
• Polycyclic Aromatic Hydrocarbons, the Anomalous Microwave Emission, and Their Connection to the Cold Neutral Medium
• Anisotropies in the HI gas distribution toward 3C196
• Autonomous Gaussian decomposition of the Galactic Ring Survey. I. Global statistics and properties of the 13CO emission data
• GASKAP-HI Pilot Survey Science III: An unbiased view of cold gas in the Small Magellanic Cloud
• GASKAP Pilot Survey Science II: ASKAP Zoom Observations of Galactic 21-cm Absorption
• Non-Gaussian modelling and statistical denoising of Planck dust polarization full-sky maps using scattering transforms
• BICEP / Keck XVI: Characterizing Dust Polarization through Correlations with Neutral Hydrogen
• Detecting the non-Gaussianity of the 21-cm signal during reionisation with the Wavelet Scattering Transform
• Centrally Concentrated H I Distribution Enhances Star Formation in Galaxies
• Exploration of 3D wavelet scattering transform coefficients for line-intensity mapping measurements
• Mapping the Thermal Condensation of Diffuse H I in the North Celestial Pole Loop
• Exploring Hydrodynamic Instabilities along the Infalling High-Velocity Cloud Complex A
• The physical and the geometrical properties of simulated cold HI structures
• The MACH HI absorption survey I: Physical conditions of cold atomic gas outside of the Galactic plane

Cited by in corpus (6)

• Full-sky Models of Galactic Microwave Emission and Polarization at Sub-arcminute Scales for the Python Sky Model
• Filamentary Dust Polarization and the Morphology of Neutral Hydrogen Structures
• Generative models of astrophysical fields with scattering transforms on the sphere
• A neutral hydrogen absorption study of cold gas in the outskirts of the Magellanic Clouds using the GASKAP-HI survey
• Quantitative Morphology of Galactic Cirrus in Deep Optical Imaging
• A New Wavelet Scattering Transform-Based Statistic for Cosmological Analysis of Large-Scale Structure