Molecular gas along the bar of NGC 7479

We present new SOFIA observations of [CII] emission from the nearby asymmetric barred spiral galaxy NGC 7479. The data have been obtained with FIFI-LS and cover a field of approximately 70′′×114′′including the whole bar of the galaxy. We analyze the [CII] emission in conjunction with a wealth of existing optical, infrared and radio data. In particular, we compare the [CII] emission with unpublished archival ALMA CO and Hα data in the same region to better understand the kinematics and origin of the molecular gas along the bar. To study the origin of the [CII] emission, we compared it to CO emission, and mid-IR and far-IR star formation indicators. We conclude that the [CII] emission along the bar is mainly due to molecular gas, with a few exceptions. In particular, the two ends of a jet-like feature visible in the radio continuum appear to be more luminous in [CII] than what is expected based on the CO emission. The low level of CO emission at the northern end of the jet can be due to the low metallicity of the gas which is usually under-luminous in CO. The southern end of the jet has also an excess of [CII] emission with respect to mid-IR and far-IR diagnostics of star formation. Because there is little atomic gas (neutral or excited) at this location, the [CII] emission probably originates in shocked molecular gas. In addition, at two locations the CO/[CII] ratio is anomalously low, showing the existence of patches of dark-CO molecular gas in particular environments of this galaxy. The [CII] and CO observations also allow us to better understand the gas kinematics. Two main velocity components are most evident in the bulge. Moreover, the northern knot of the bar, claimed to be associated with minor merging, shows two velocity components in the [CII] emission. Finally, a component of cold molecular gas is seen in CO trailing the bar in the sense of the rotation of the galaxy.