High‐Latitude Hiin NGC 2613: Buoyant Disk‐Halo Outflow

We combine new VLA D array HI data of NGC 2613 with previous high resolutiondata to show new disk-halo features in this galaxy. The global HI distributionis modeled in detail using a technique which can disentangle the effects ofinclination from scale height and can also solve for the average volume densitydistribution in and perpendicular to the disk. The model shows that thegalaxy's inclination is on the low end of the range given by Chaves & Irwin(2001) and that the HI disk is thin (z_e = 188 pc), showing no evidence forhalo. Numerous discrete disk-halo features are observed, however, achieving zheights up to 28 kpc from mid-plane. One prominent feature in particular, ofmass, 8X10^7 Msun and height, 22 kpc, is seen on the advancing side of thegalaxy at a projected galactocentric radius of 15.5 kpc. If this featureachieves such high latitudes because of events in the disk alone, then inputenergies of order ~ 10^{56} ergs are required. We have instead investigated thefeasibility of such a large feature being produced via buoyancy (with drag)within a hot, pre-existing X-ray corona. Reasonable plume densities,temperatures, stall height (~ 11 kpc), outflow velocities and ages can indeedbe achieved in this way. The advantage of this scenario is that the inputenergy need only be sufficient to produce blow-out, a condition which requiresa reduction of three orders of magnitude in energy. If this is correct, thereshould be an observable X-ray halo around NGC 2613.Comment: 32 pages 7 gif figures, accepted by Ap