Power Spectrum Analysis of the OMC1 Image at 1.1 mm Wavelength

We present a 1.1mm emission map of the OMC1 region observed with AzTEC, a new large-format array composed of 144 silicon-nitride micromesh bolometers, that was in use at the James Clerk Maxwell Telescope (JCMT). These AzTEC observations reveal dozens of cloud cores and a tail of filaments in a manner that is almost identical to the submillimeter continuum emission of the entire OMC1 region at 450 and 850 micronm. We perform Fourier analysis of the image with a modified periodogram and the density power spectrum, which provides the distribution of the length scale of the structures, is determined. The expected value of the periodogram converges to the resulting power spectrum in the mean squared sense. The present analysis reveals that the power spectrum steepens at relatively smaller scales. At larger scales, the spectrum flattens and the power law becomes shallower. The power spectra of the 1.1mm emission show clear deviations from a single power law. We find that at least three components of power law might be fitted to the calculated power spectrum of the 1.1mm emission. The slope of the best fit power law, \gamma ~ -2.7 is similar to those values found in numerical simulations. The effects of beam size and the noise spectrum on the shape and slope of the power spectrum are also included in the present analysis. The slope of the power law changes significantly at higher spatial frequency as the beam size increases.Comment: 7 pages, 2 figures, Journal of the Korean Astronomical Society, vol. 45, pp.93-99; For Figure 1, please refer to http://jkas.kas.org/journals/2012v45n4/v45n4p093_skim.pd

The Multi-Phase Medium in the Interstellar Complex N44

We have obtained high-resolution HI observations of N44, one of the largest HII complexes in the Large Magellanic Cloud. The distribution and internal motions of the HI gas show dynamic effects of fast stellar winds and supernova blasts. Numerous HI holes are detected, with the most prominent two corresponding to the optically identified superbubbles Shell 1 and Shell 2. The HI gas associated with Shell 1 shows an expansion pattern similar to that of the ionized gas shell, but the mass and kinetic energy of the HI shell are 3--7 times those of the ionized gas shell. The total kinetic energy of the neutral and ionized gas of Shell 1 is still more than a factor of 5 lower than expected in a pressure-driven superbubble. It is possible that the central OB association was formed in a molecular cloud and a visible superbubble was not fully developed until the ambient molecular gas had been dissociated and cleared away. This hypothesis is supported by the existence of a molecular cloud toward N44 and the fact that the apparent dynamic age of the superbubble Shell 1 is much shorter than the age of its OB association LH47. Accelerated HI gas is detected at the supernova remnant 0523-679. The mass and kinetic energy in the associated HI gas are also much higher than those in the ionized gas of 0523-679. Studies of interstellar gas dynamics using ionized gas alone are clearly inadequate; neutral gas components must be included.Comment: 18 pages,5 figures; for "figures", see at "http://www.astro.uiuc.edu/~sek/N44.html" (4.9 MB postscript.gz) ; Appear to ApJ, 503, 729 (Aug 20

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 nearby disk galaxies. This method is applied successfully to the Australia Telescope Compact Array interferometric HI survey of the Large Magellanic Cloud (LMC); it could also be applied to a significant number of nearby disk galaxies, thanks to the next generation of interferometric facilities, such as the extended VLA and CARMA. The method consists of computing the Spectral Correlation Function (SCF) for a spectral-line map of a face-on galaxy. The SCF quantifies the correlation between spectra at different map positions as a function of their separation, and is sensitive to the properties of both the gas mass distribution and the gas velocity field. It is likely that spatial correlation properties of the gas density and velocity fields in a galactic disk are sensitive to the value of the scale height of the gas disk. A scale-free turbulent cascade is unlikely to extend to scales much larger than the disk scale height, as the disk dynamics on 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 of approximately 180 pc, which we identify as the disk scale height. We are also tentatively able to map variations of the scale height over the disk.Comment: 6 pages, submitted to ApJ