📝 SummarXiv

Abstract

We report the discovery of a kpc scale molecular contrail in the spiral galaxy NGC 3627, a narrow structure spanning 8 kpc in length with a width of 200 pc and an extreme aspect ratio of 40, observed in both mid-infrared dust emission (PHANGS-JWST) and CO(2-1) gas (PHANGS-ALMA). This contrail size significantly exceeds the size of any known analogs in the Milky Way and exhibits supersonic turbulence (10 km/s). Its morphology and dynamics are consistent with gravitational focusing by a flyby compact object of mass 1e6 M_sun, likely a massive black hole or a dwarf galaxy nucleus, traversing the disk at >300 km/s. The crossing time of such a contrail, estimated from its width and velocity dispersion, is only $\sim 20$ Myr, implying a recent interaction. This contrail can be caused by a dwarf galaxy, or massive black hole nucleus. This discovery establishes galactic-scale contrails as probes of massive dark objects interacting with medium in and around galactic disks.