Extraplanar gas in Edge-on Galaxies traced by SOFIA observations of [C II]

TL;DR

This study uses SOFIA observations to analyze the vertical distribution of [C II] emission in edge-on galaxies, revealing a thin and a thick disk component and the extent of extraplanar gas related to star formation activity.

Contribution

It provides new measurements of [C II] vertical distribution in edge-on galaxies, highlighting the presence of a thick disk and the extent of extraplanar gas beyond star-forming regions.

Findings

[C II] emission extends beyond star-forming regions but less than H I gas.

A thin 0.3 kpc disk is supplemented by a 2 kpc thick disk in the galaxies.

Extraplanar [C II] may originate from chimneys connecting disk and halo.

Abstract

Bursts of localized star formation in galaxies can levitate material from their midplanes. Spiral galaxies that are edge-on allow clear distinction of material that is levitated off the galaxies' midplanes. We used SOFIA to measure the vertical distribution of [C II] 157.7 micron line emission for two nearby, edge-on galaxies, NGC 891 and NGC 5907. We find that for the central region and actively-star-forming regions in the northern portion of NGC 891, and for NGC 5907, a thin (0.3 kpc) disk is supplemented by a thick disk with an exponential scale height of about 2 kpc. The [C II] is far more extended than mid-infrared emission (0.1 kpc, tracing present-day massive star formation) but not as extended as the H I (100 kpc, tracing low-metallicity circum/inter-galactic matter). The extraplanar [C II] may arise in walls of chimneys that connect the disk to the halo.