You can live stream audio and video, but only Publish / Archive an audio file following the broadcast, if desired.
Note: even if you stream audio only through your encoder (no video) you must still activate this option (turn on Publish Audio Only) in order to prevent the system from trying to create a video file.
Live Episode within Studio… Live Broadcast tab > Settings & URLS section:
According to this illustration (above), following the Live Stream the Studio will automatically create a new Episode in the Archive and automatically Publish only an audio file to it. No video will be created.