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Park et al. present HI (neutral hydrogen) gas kinematics and star
formation activity in NGC 6822, a dwarf galaxy located in our Local
Group of galaxies at a distance of 1.6 million light-years (490
kilo-parsecs). They performed profile decomposition of line-of-sight
velocity profiles of archival HI data taken with the Australia
Telescope Compact Array (ATCA). The large HI gas disk of the galaxy
with a major axis of ~1 degree was observed through a mosaic of eight
pointings with the ATCA. The top left panel above shows a
multi-wavelength color-composite image of NGC 6822 using the
integrated flux density map from ATCA HI 21cm (gray), GALEX FUV
(blue), and WISE 22 µm (yellow) data. The top right, bottom left, and
bottom right panels show "moment" maps: moment0 shows the integrated
flux density, moment1 the intensity-weighted mean velocity, and
moment2 the intensity-weighted velocity dispersion. Two notable
features in the HI gas distribution of NGC 6822 (the moment0 map) are
the companion HI cloud located in the northwestern (top-right) region
of the galaxy, and the supergiant HI shell occupying a large area of
the disk in the southeastern region. The team used a new tool to
classify the decomposed HI gas components of NGC 6822 into cool-bulk,
warm-bulk, cool-non-bulk and warm-non-bulk motions with respect to
their centroid velocities and velocity dispersions.
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