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RE: NGC 6503
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Lonely Galaxy 'Lost in Space'

This magnificent spiral galaxy is at the edge of what astronomers call the Local Void. The Local Void is a huge volume of space that is at least 150 million light-years across that doesn't seen to contain anything much. There are no obvious galaxies. This void is simply part of the structure of the universe where matter grows clumpy over time so that galaxies form clusters and chains, which are separated by regions mostly devoid of galaxies.
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NGC 6503 (also IRAS 17499+7009, MCG+12-17-009, UGC 11012 and PGC 60921) is a magnitude +10.2 dwarf spiral galaxy located 17 million light-years away in the constellation Draco.

The galaxy was discovered by the German astronomer Georg Friedrich Julius Arthur von Auwers using a 6.6 cm (2.6-inch) Fraunhofer refracting telescope in Göttingen on the 22nd July 1854.

NGC 6503

Right Ascension: 17h 49m 27.5s, Declination: +70° 08' 37"

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Title: Aperture Synthesis Observations of the Nearby Spiral NGC 6503: Modelling the Thin and Thick HI Disks
Authors: Eric W. Greisen, Kristine Spekkens, Gustaaf A. van Moorsel

We present sensitive aperture synthesis observations of the nearby, late-type spiral galaxy NGC 6503, and produce HI maps of considerably higher quality than previous observations by van Moorsel & Wells (1985). We find that the velocity field, while remarkably regular, contains clear evidence for irregularities. The HI is distributed over an area much larger than the optical image of the galaxy, with spiral features in the outer parts and localized holes within the HI distribution. The absence of absorption towards the nearby quasar 1748+700 yields an upper limit of 5 10^{17} cm^{-2} for the column density of cold HI gas along a line of sight which should intersect the disk at a radius of 29 kpc. This suggests that the radial extent of the HI disk is not much larger than that which we trace in HI emission (23 kpc). The observed HI distribution is inconsistent with models of a single thin or thick disk. Instead, the data require a model containing a thin disk plus a thicker low column-density HI layer that rotates more slowly than the thin disk and that extends only to approximately the optical radius. This suggests that the presence of extra-planar gas in this galaxy is largely the result of star formation in the disk rather than cold gas accretion. Improved techniques for interferometric imaging including multi-scale Clean that were used in this work are also described.

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