The Discovery of the Largest Gas Filament in Our Galaxy, or a New Spiral Arm?
Abstract
Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we detect a giant H I filamentary structure in the sky region of 307°7 < α < 311°0 and 40°9 < δ < 43°4. The structure has a velocity range of -170 to -130 km s-1, and a mean velocity of -150 km s-1, putting it at a Galactocentric distance of 22 kpc. The H I structure, which we name Cattail, has a length of 1.1 kpc, which so far appears to be the furthest and largest giant filament in the Galaxy. Its mass is calculated to be 6.5 × 104 M⊙ and the linear mass density is 60 M⊙ pc-1. Its width is 207 pc, corresponding to an aspect ratio of 5:1. Cattail possesses a small velocity gradient (0.02 km s-1 pc-1) along its major axis. Together with the HI4PI data, we find that Cattail could be even longer, up to 5 kpc. We also identify another new elongated structure as the extension into the Galactic first quadrant of the Outer Scutum-Centaurus (OSC) arm, and Cattail appears to be located far behind the OSC arm. The question about how such a huge filament is produced at this extreme Galactic location remains open. Alternatively, Cattail might be part of a new arm beyond the OSC arm, though it is puzzling that the structure does not fully follow the warp of the Galactic disk.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2021
- DOI:
- 10.3847/2041-8213/ac19bc
- arXiv:
- arXiv:2108.01905
- Bibcode:
- 2021ApJ...918L...2L
- Keywords:
-
- Interstellar filaments;
- Interstellar atomic gas;
- 842;
- 833;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 10 pages, 7 figures, Accepted for publication in ApJL