A Catalog of Filaments in the Central Molecular Zone

TL;DR

The paper tackles the challenge of characterizing a large population of filaments in the Galactic center by applying automated detection to MeerKAT $1.28\ \mathrm{GHz}$ continuum data. It repurposes the OCCULT-based loop tracing software (looptracing_auto4) to produce a main, per-point catalog and a summary, per-filament catalog, including $I_\nu$, $L$, $\alpha$, and curvature measurements with a corrected brightness factor of $0.1315$. The authors propose objective selection criteria to isolate nonthermal filaments (NRFs) from SNRs and H II regions, and discuss catalog completeness and processing limitations. The catalog enables population-level studies of NRFs in the CMZ and facilitates multi-wavelength comparisons and statistical inferences about filament morphology and spectra.

Abstract

We present a catalog of 1.28 GHz radio filaments observed by MeerKAT over the innermost 200 pc of the Galaxy (roughly $\pm 1.5°$), which includes the central molecular zone (CMZ). The catalog is generated by repurposing software developed for the automated detection of filaments in solar coronal loops. There are two parts to the catalog. The first part, the main catalog, provides a point-by-point listing of locations and basic observational properties along each detected filament. The second part is a summary catalog which provides a listing of mean, median, or total values of various properties for each filament. Tabulated quantities include position, length, curvature, brightness, and spectral index. The catalogs contain a heterogeneous mix of filamentary structures, including nonthermal radio filaments (NRFs), and parts of supernova remnants (SNRs) and thermally emitting regions (e.g. H II regions). We discuss criteria for selecting useful subsamples of filaments from the catalogs, and some of the details encountered in examining filaments or selections of filaments from the catalogs.

Figures (6)

• Figure 1: Histogram of filament widths. The red dashed line (at 2.25 pix $= 2.475"$) indicates an adopted separation between likely real filaments and artificially narrow artifacts. The Gaussian smoothing applied to the data ($\sigma_1 = 2.75"$, Section \ref{['sec:data']}) leads to a smoothed beam with $\sigma = 3.23"$ in the filtered image.
• Figure 2: Map of filaments with selection criteria indicated by color. Gray indicates width $\sigma_{\rm g} < 2.475"$. Wider filaments are colored blue for lengths $33" < L < 66"$, green for $66" < L < 132"$, and red for $132" < L$.
• Figure 3: Map of filament spectral indices. Thermal emission with $\alpha \gtrsim -0.1$ (yellow to red) appears mostly as short filaments with little organization at $|b| < 0.2\arcdeg$. Supernova remnants with $\alpha \approx -0.7$ (green) appear as rounded clusters of curved filaments. The nonthermal radio filaments are more linear, oriented vertically, and generally have somewhat steeper spectral indices (blue).
• Figure 4: Map of filament curvatures. Many of the straightest filaments ($\rho \approx 0$) can be recognized as long nonthermal radio filaments here.
• Figure 5: Finder chart for catalog filaments having widths $\sigma_{\rm g} > 2.475"$. Each filament is labeled with its catalog number, but the numbers are very small to minimize confusion and the PDF-format figure must be magnified to read them. The filaments and numbers are color coded by filament length (in arc seconds) to also help filament identification.