A New Method to Measure and Map the Gas Scale Height of Disk Galaxies

We propose a new method to measure and map the gas scale height of nearbydisk galaxies. This method is applied successfully to the Australia TelescopeCompact Array interferometric HI survey of the Large Magellanic Cloud (LMC); itcould also be applied to a significant number of nearby disk galaxies, thanksto the next generation of interferometric facilities, such as the extended VLAand CARMA. The method consists of computing the Spectral Correlation Function (SCF) fora spectral-line map of a face-on galaxy. The SCF quantifies the correlationbetween spectra at different map positions as a function of their separation,and is sensitive to the properties of both the gas mass distribution and thegas velocity field. It is likely that spatial correlation properties of the gasdensity and velocity fields in a galactic disk are sensitive to the value ofthe scale height of the gas disk. A scale-free turbulent cascade is unlikely toextend to scales much larger than the disk scale height, as the disk dynamicson those larger scales should be dominated by two dimensional motions. We find a clear feature in the SCF of the LMC HI disk, on the scale ofapproximately 180 pc, which we identify as the disk scale height. We are alsotentatively able to map variations of the scale height over the disk.Comment: 6 pages, submitted to ApJ