Extraplanar Gas in Edge-on Galaxies Traced by SOFIA Observations of [C ii]

Abstract

Bursts of localized star formation in galaxies can levitate material from the midplane. Spiral galaxies that are edge-on allow a clear distinction of material that is levitated off the galaxies’ midplanes. We used SOFIA to measure the vertical distribution of [C ii ] 157.7 μ m 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 ∼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/intergalactic matter). The extraplanar [C ii ] may arise in walls of chimneys that connect the disk to the halo.