astronomy - Does the Milky Way have dark matter satellite galaxies?

This recent paper by Weinberg et al. discusses that one potential problem with our current model of Cold Dark Matter (CDM) is that is predicts a greater number of satellite galaxies for the Milky Way than are actually observed, and satellite galaxies with larger masses than those the Milky Way has (although the paper does say that many of the Milky Way's satellite galaxies may be too dim for us to currently observe).

I know that at least dark matter galaxies are believed to have been observed (see this article). Is there any observational or other evidence for the existence of dark matter satellite galaxies to the Milky Way? And how have they been found?

Edit: As has been pointed out, this is a question we likely don't have the answer to yet (otherwise there wouldn't be recent papers posing the question still), so perhaps a better question would be how could/would you find dark matter satellite galaxies of the Milky Way?

Answer

This is actually a problem between simulations of structure formation and observations on a couple of different mass scales. Both galaxies and galaxy clusters appear to have nearly an order of magnitude more satellites than what is actually observed. The problem is dubbed the "missing satellite problem", or the Dwarf galaxy problem.

People have been asking the question, what if these dwarf galaxies are simply not massive enough to attract enough gas gravitationally for them to be visible? Some interesting ideas and work has been done to determine if these structures actually do exist (Yoon, Johnston, and Hogg - Clumpy Streams from Clumpy Halos: Detecting Missing Satellites with Cold Stellar Structures). Also, Beth Willman has done some interesting work on detecting the least luminous galaxies (dwarf galaxy companions to the Milky Way). In other words, it is quite possible that there are small collections of stars, dust, and gas inside these substructures that are just so faint, we can't find them unless we're looking closely.

I should also add that people have gone to lengths in the other direction, too. That is, to see how to alter the properties of dark matter in order to rid simulations of structures on that particular scale (see: Self-interacting dark matter).

The LCDM cosmological model is a very robust and well-supported model for our universe on scales of around ~1 Mpc and larger. Some discrepancies do exist, of which the missing satellite problem is but one of them.