The Mid-Infrared is good to study hot gas and dust in close galaxies. The Spitzer Space Telescope did already study the gas in close galaxies, like the spiral Andromeda galaxy or the dwarf galaxies Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC).
Beside these very close galaxies, spitzer did image more distant galaxies, as it studied the Milky Way and those galaxies.
One of the most impressive images is the galaxy ESO 30-9 and I have combined the DSS2 (optical) and spitzer data (mid-infrared) into one image:
You can clearly see four spiral arms as red parts of the image, representing the mid-infrared. The GLADE catalog does show a distance of 114 Mega parsec.
Other good images of galaxies:
Those galaxies are closer than ESO 30-9, but they are less detailed, because more stars are between the galaxies and the telescope and they are smaller. Additionally there is gas and dust in our own milky way, producing a lot of noise.
Two galaxies have special features. One looked like a elliptical galaxy, but with some scaling there appeared a bright ring around the centre of the galaxy:
So my guess is that it has a nuclear ring or a lensed background galaxy.
Another special galaxy is this spiral galaxy, seen edge-on:
As you can see there are red parts close the the centre. Those are the spiral arms that otherwise would have been invisible.
There are also a lot galaxies that are not in any catalog:
The next space telescope that can image the mid-infrared in high resolution is the James Webb Space Telescope (JWST). The Webb does carry the Mid-Infrared Instrument (MIRI).
MIRI does have a resolution 5 times better than spitzer.
Another big improvement is the sensitivity, which is 50 times better than spitzer. Two things make this possible: The gold-coated segmented mirror, the cryocooler, which cools the MIRI to Gold does reflect the infrared very good and the instrument does have to be cooled to low temperatures, so it does not detect the “heat radiation” (infrared) from itself. The large sun shield already cools the entire telescope to -233°C, so no radiation from the sun does harm the detection.
But the MIRI will not only see the relative close galaxies, but also the most distant galaxies in the Universe, born short after the big bang. Because the light from those galaxies is redshifted to longer wavelengths, they are visible in the mid-infrared. Short after the JWST does begin taking data, it will image some of the Deep Fields. Maybe there will be some surprises, like when Hubble did image the Hubble Deep Field for the first time and astronomers were surprised that this “black part of the sky” was crowded with distant galaxies.
List of spitzer galaxies.