NGC 6822 Barnard's Galaxy

OTA: CDK17

Camera: SBIG STXL11002with AOX and FW8G (0.63 arsec/pxl)

Observatory: Heaven’s Mirror, Chile

EXPOSURES:

Red: 16 x 1200 sec.

Blue: 17 x 1200

Green: 13 x 1200

L: 14 x 1800

H: 15 x 1800

Total exposure 30 hours

Image Width: ~35 arc-minutes

Processed by Alex Woronow (2020) using PixInsight, Skylum, Topaz, SWT

NGC 6822 lies about 1.6Mly from us and holds membership in our Local Group. Being a Dwarf Galaxy, It bears a resemblance to the Small Magellanic Cloud. NGC 6822 holds two historic distinctions: First, it was discovered in the year 1884 using a 6” refractor by its namesake, E. E. Barnard, and secondly, it was the first galaxy beyond the Magellanic nebulae to have its distance determined by use of Cepheid variables. Of course, Hubble did the second task. Although he came up a bit short of the actual distance, estimating the distance at just under 700,000 lys., it was the analysis that extended the size of our Universe beyond the Milky Way Galaxy.

Several reddish clouds, HII clouds, lie within and about this galaxy—Hubble discovered 5 of them and recognized them has HII clouds similar to the Great Nebula in Orion. He saw others, such as appear in this image, but attributed them to galaxies lying beyond NGC 6822—well, that was a mistake, but not fatal to his distance-measurement breakthrough.

A companion cloud of HI (neutral hydrogen) engulfs NGC 6822 and hosts many young blue stars (Blok & Walter). These stars persist down to at least 25th magnitude, according to their study. My image goes significantly deeper than 21st magnitude but certainly does not reach 25th magnitude. (The preceding statement reflects comparison my image to the stars produced by MaskGen.) Still, my image also shows the decreasing radial abundance of faint blue stars and suggesting their association with Mr. Barnard’s Galaxy and the HI zone. The spatial distributions of the blue stars and the density of the HI cloud appear correlated. Blok and Walter conclude the correlation arose from a star-forming event sometime greater than 10^8 years ago.

Just for fun, see if you see what I see: a ragged, somewhat dark halo around the galaxy. Could that be the HI region blocking light from more distant stars? These galaxy-encasing dark halos appear frequently.