606 research outputs found
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
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