It's always in the last place you look

Traditionally* the missing satellite problem refers to the lack of satellite galaxies detected in our Local Group compared to theoretical predictions. It's only in this nearest region that we can reach the sensitivity needed to be able to spot the faintest smudges of the smallest galaxies. Which means it's always been possible that our Local Group is in some way peculiar, with other galaxies having multitudinous swarms of tiny satellites that we just can't see. It would certainly be great to have better data of more distant galaxies so we can see how typical our little patch of the cosmos really is.

* Since 1999. That's traditional now.

This paper presents observations of the NGC 3175 group of galaxies, which is reasonably similar to our own group but about 14 Mpc (45 million light years) away. Using deep, but not extraordinarily so, 2.5 hour observations on a 2.2 m telescope, they claim to have detected ~550 candidate dwarf galaxies : far more than the 100-odd satellites in the Local Group. So, super interesting ?

I'd have to say no, not really. I'm not at all convinced by the methodology here. They don't state the surface brightness sensitivity of their observations and their detection method seems dicey. All (or almost all) of those recent "ultra diffuse galaxies" have been detected by basically the same method : doing deep observations of both the target field and a background control field. That way the search method can be tested. What it should do - and what the UDG papers demonstrate successfully - is find stuff only in the target field, so you can be pretty confident that most of the detections are really associated with the known group or cluster of galaxies. That means you can say they're probably at a similar distance, which is much easier to measure for the big bright galaxies (and damned hard for the faintest ones).

That's not what they do here : they just have the target field, and no control. They decide if the galaxies are likely to be in the group or not based on their structural parameters. The UDG papers do this too, but they don't rely on them this heavily. While I don't doubt that this can indeed remove lots of contaminating background objects, e.g. angularly tiny galaxies with spiral arms are almost certainly distant background objects, it's not at all clear it's a good way to remove all the background objects, much less how much foreground contamination there is. The discovery of large numbers of UDGs, which could easily be mistaken for dwarves except they're known to actually be large and far away, makes this kind of method questionable at best. It's also rather worrying that they dismiss UDGs as unimportant :
"...these UDGs are just a subset of dwarf elliptical galaxies found mostly in rich clusters of galaxies."
Oh well, one man's revolution in the field is another's blasé event of tedious mediocrity.

(The third author has mentioned the unimportance of UDGs before and is quite clearly bitter about his own similar discoveries being overlooked - to some extent quite understandably so, but it's the large numbers of these objects that's really got people interested.)

The other crucial thing lacking here is a discussion on the environment of the group. On the small scale, it would be extremely interesting to see the positions of the galaxies - with >500 objects we could perhaps see those damn planes I hate so much or if they were at least denser nearer to the centre of the group. And we need a discussion of the background environment - maybe there are background clusters or groups we might expect to host UDGs and so cause contamination. They could have at least have calculated the distance beyond which their candidates would be unfeasibly large. But they don't do any of that. The radii given in their (truncated - though it's possible the full version will be available when it's actually published in MNRAS) main table (which is not referenced in the text) are very much smaller than that of UDGs, and their Sersic indicies (a measure of the shape of their light profile) are similar, so it's entirely reasonable to suggest that many of them could be much more distant objects.

Assuming this result is correct, then the numbers they found are a bit less than the classical simulations predict, but a bit more than the more modern versions which have far more physics. But there are so many uncertainties at the moment that this could simply be meaningless, so there's not much point speculating about it.
http://adsabs.harvard.edu/abs/2018arXiv180809020K