Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

A Catalog of Galactic Atomic Hydrogen Position-Position-Velocity Filaments

M. E. Putman, D. A. Kim, S. E. Clark, L. Li, C. Holm-Hansen, J. E. G. Peek

TL;DR

The paper tackles the 3D distribution and physical properties of Galactic HI filaments in PPV space by constructing a comprehensive 3D filament catalog from GALFA-HI DR2. It introduces fil3d, a 3D extension of FilFinder, uses per-channel HI data with unsharp masking to remove large-scale emission, and links 3D structures across velocity to form PPV filaments; the catalog comprises 3333 filaments within ±50 km s^-1. Filament properties show a characteristic width of ~12' ($0.34$ pc at $100$ pc) with HI column densities around $N_{ m HI} obreak\ sim obreak 6 imes10^{18}\,\mathrm{cm^{-2}}$, local filaments having FWHM ~ 3.2 km s^-1 and length ~ 6.4 pc, while disk-halo filaments exhibit similar column densities but broader FWHM ~ 7.7 km s^-1. The results reveal a hierarchical, sky-bundled organization consistent with a turbulence-driven formation process, as indicated by the L ∝ M^{0.5} relation, and demonstrate a practical tool for large-scale ISM studies and magnetic-field context.

Abstract

We present a catalog of 3D Galactic HI filaments over 1/3 of the sky using Galactic Arecibo L-band Feed Array HI (GALFA-HI) data. The 3D filaments are defined to be linear HI features that are continuous in position-position-velocity (PPV) and are found with fil3d, an algorithm that expands on the 2D FilFinder. The catalog contains 3333 HI filaments between +/- 50 km/s at a range of Galactic positions. 1542 of the PPV filaments are identified as local at the distance of the wall of the Local Bubble, and 209 are likely at the disk-halo interface of our Galaxy. The catalog and properties of the PPV filaments are obtained after an unsharp mask (USM) is applied to the data. The widths of the filaments are consistently ~12' (0.34 pc at 100 pc), and constrained by the 4' resolution. The local filaments have median properties of N_HI = $6 \times 10^{18}$ cm$^{-2}$, M_HI = 0.17 M_sun, FWHM = 3.2 km/s, and length of 6.4 pc. The disk-halo population has similar column densities, but the median FWHM = 7.7 km/s, consistent with them being higher z-height, warmer structures. The L $\propto$ M$^{0.5}$ relationship found for the HI filaments and their bundling on the sky are consistent with a hierarchical structure, and is likely related to turbulence playing a role in their formation.

A Catalog of Galactic Atomic Hydrogen Position-Position-Velocity Filaments

TL;DR

The paper tackles the 3D distribution and physical properties of Galactic HI filaments in PPV space by constructing a comprehensive 3D filament catalog from GALFA-HI DR2. It introduces fil3d, a 3D extension of FilFinder, uses per-channel HI data with unsharp masking to remove large-scale emission, and links 3D structures across velocity to form PPV filaments; the catalog comprises 3333 filaments within ±50 km s^-1. Filament properties show a characteristic width of ~12' ( pc at pc) with HI column densities around , local filaments having FWHM ~ 3.2 km s^-1 and length ~ 6.4 pc, while disk-halo filaments exhibit similar column densities but broader FWHM ~ 7.7 km s^-1. The results reveal a hierarchical, sky-bundled organization consistent with a turbulence-driven formation process, as indicated by the L ∝ M^{0.5} relation, and demonstrate a practical tool for large-scale ISM studies and magnetic-field context.

Abstract

We present a catalog of 3D Galactic HI filaments over 1/3 of the sky using Galactic Arecibo L-band Feed Array HI (GALFA-HI) data. The 3D filaments are defined to be linear HI features that are continuous in position-position-velocity (PPV) and are found with fil3d, an algorithm that expands on the 2D FilFinder. The catalog contains 3333 HI filaments between +/- 50 km/s at a range of Galactic positions. 1542 of the PPV filaments are identified as local at the distance of the wall of the Local Bubble, and 209 are likely at the disk-halo interface of our Galaxy. The catalog and properties of the PPV filaments are obtained after an unsharp mask (USM) is applied to the data. The widths of the filaments are consistently ~12' (0.34 pc at 100 pc), and constrained by the 4' resolution. The local filaments have median properties of N_HI = cm, M_HI = 0.17 M_sun, FWHM = 3.2 km/s, and length of 6.4 pc. The disk-halo population has similar column densities, but the median FWHM = 7.7 km/s, consistent with them being higher z-height, warmer structures. The L M relationship found for the HI filaments and their bundling on the sky are consistent with a hierarchical structure, and is likely related to turbulence playing a role in their formation.

Paper Structure

This paper contains 6 sections, 1 figure.

Table of Contents

  1. Introduction
  2. The GALFA-HI Data
  3. Extracting 3D Filaments
  4. Starting with the 2D FilFinder
  5. fil3d: The 3D Filament Finder
  6. Selection cuts for the 3D filament catalog

Figures (1)

  • Figure 1: Moment 0 maps of example 3D HI filaments from the local (left two columns) and disk-halo (right two columns) populations. The red or green contour lines are the filament masks as identified by fil3d and the background is the USM GALFA-HI data (labelled "USM") for the first column of each population and the original raw data for the second column (labelled "RAW"), integrated over the FWHM velocity width. The axes are in pixels which are 1$^\prime$. It is evident that the USM successfully extracts the filament, but also removes a diffuse component that affects the derived column densities and widths.