Speaker
Description
I will present high resolution, ultra-deep HI images of the nearby, newly discovered interacting NGC 4781 triplet, observed by MeerKAT as part of the MHONGOOSE survey. The triplet is situated at 11 Mpc, and consists of two late types and one dwarf irregular galaxy. The global properties and scaling relations are consistent with other late type, star forming galaxies of the same stellar mass. However, the diffuse (10^17 - 10^18 cm^-2) HI component shows a remarkable new scenario of interacting galaxies. There is extensive (~ 50 kpc) extra-planar HI gas associated with the two late type galaxies as well as an extended HI tail complex that connects the two satellite galaxies. The HI velocity field shows many diffuse components that are not associated with the rotating disk, and both late types contain large coherent arcs of HI with a high (30 - 80 km s^-1) velocity dispersion, well outside the stellar disk. Two quick, successive flybys that tidally disturbed the diffuse HI but left the HI in the disk and stellar component largely untouched, is likely responsible for the observed properties. We compute the timescale of the flybys and compare it to similar galaxies in the SIMBA simulations. We predict it is very common for late-type, star-forming galaxies in close (e.g. < 100 kpc) proximity to host diffuse, extensive HI complexes, however, only now do we have the sensitivity and resolution to detect them.
