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Thank you, Dana, for the very interesting observations and summary about Sextans A.
(there are some rude people who like to call it Sex A)
This isn't characteristic of my approach to astronomy, but......"Ooh, look at that pretty little diamond-shaped galaxy!"
(at present, I am fully occupied trying to figure out the meaning of sjastro's recent UV observations of NGC 5128, and I am also working on the morphology of NGC 2442)
cheers, mad galaxy man
P.S.
I have observed NGC 3109 many times, and, as with all irregular galaxies which are at or just beyond the fringes of the Local Group, the sky conditions are the determining factor for successful observations rather than the aperture used.
The 'morphology-density' relationship which was discovered by Alan Dressler 30 years ago, holds up very well in the Local Group and in the nearby groups of galaxies; the dwarf irregular galaxies are found preferentially in the lowest density regions, and the dwarf spheroidal galaxies are found in the highest density regions (usually near to the large galaxies)
One question that comes to mind when one contemplates a very-isolated dwarf irregular, with little apparent material of any sort existing within a vast distance from it, is "why should a galaxy form at all in such an isolated place?"
However, the intergalactic medium is only now being characterised by professional astronomers , and there is more gas out there between the galaxies than one would naively think.
For the most part, dwarf irregular galaxies can continue to form stars for a long time, as they are noted for having large reservoirs of Neutral Atomic Hydrogen gas, from which new stars can continue to form. Also, the typical dwarf irregular has a very low time-rate of formation of stars, and star formation in these little galaxies is very bursty in nature.
(the best known examples are not typical of dwarf irregular galaxies)
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