A High-Velocity Cloud Impact Forming a Supershell in the Milky Way

Abstract

Neutral atomic hydrogen (HI) gas in interstellar space is largely organized into filaments, loops, and shells, the most prominent of which are "supershells". These gigantic structures requiring $\gtrsim 3\times 10^{52}$ erg to form are generally thought to be produced by either the explosion of multiple supernovae (SNe) in OB associations or alternatively by the impact of high-velocity clouds (HVCs) falling to the Galactic disk. Here we report the detection of a kiloparsec (kpc)-size supershell in the outskirts of the Milky Way with the compact HVC 040+01$-$282 (hereafter CHVC040) at its geometrical center using the "Inner-Galaxy Arecibo L-band Feed Array" HI 21-cm survey data. The morphological and physical properties of both objects suggest that CHVC040, which is either a fragment of a nearby disrupted galaxy or a cloud originated from an intergalactic accreting flow, collided with the disk $\sim 5$ Myrs ago to form the supershell. Our result shows that some compact HVCs can survive their trip through the Galactic halo and inject energy and momentum into the Milky Way disk.

arXiv comment10 pages, 5 figures, Accepted for publication in the Astrophysical Journal Letters on July 26, 2016

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Cited by in corpus (9)

• A Catalog of Holes and Shells in the Interstellar Medium of the LITTLE THINGS Dwarf Galaxies
• The structure and characteristic scales of the HI gas in galactic disks
• Extraplanar H II Regions in Spiral Galaxies. I. Low-Metallicity Gas Accreting through the Disk-Halo Interface of NGC 4013
• La Freccia Rossa: An IR-dark cloud hosting the Milky Way intermediate-mass black hole candidate
• GS242-03+37: a lucky survivor in the galactic gravitational field
• The Lop-sided Spiral Galaxy NGC 247: Clues to a Possible Interaction with NGC 253
• A Component of the Smith High Velocity Cloud Now Crossing the Galactic Plane
• A New Search for Star Forming Regions in the Southern Outer Galaxy
• Cosmic Rays and Non-thermal Emission Induced by Accretion of Cool Gas onto the Galactic Disk