So, as promised, I read through the original claim of evidence (not proof) of dark matter in the inner part of the Milky Way :
http://arxiv.org/abs/1502.03821
... and the "not even wrong" response :
http://arxiv.org/abs/1503.07813
... and the "your response was not even wrong"* response to the response :
http://arxiv.org/abs/1503.08784 

* They didn't actually say that, but they could have done.

Cautiously, I generally find in favour of the response by McGaugh et al. McGaugh et al.'s most important claim is that the result of the paper is that there is clear evidence of dark matter only beyond 6 kpc from the galactic center, which is not a new or surprising result. This is probably correct. Ideas about whether this is really the case or not have, however, waxed and waned (http://iopscience.iop.org/0004-637X/483/1/103/fulltext/35135.text.html#fg1)

A google search for "Milky Way rotation curve" reveals differing claims as to whether the Milky Way requires dark matter in the inner regions or not, e.g. https://squishtheory.files.wordpress.com/2013/04/rotcurve.gif vs http://pages.uoregon.edu/jimbrau/BrauImNew/Chap23/6th/23_21Figure-F.jpg
Therefore the main claim of McGaugh et al. that the paper does not present a new or surprising result appears to be substantiated.

McGaugh also make the claim that this result "follows from any plausible circular speed and Galactocentric distance for the Sun", citing a textbook I don't have. The original authors claim that this statement is factually wrong. I don't know who's right about this.

McGaugh et al. claim that the paper is confusing with its use of the term "inner". However, this is not the case. It's clear the authors mean "closer to the center of the Galaxy than the Sun". McGaugh et al. also state the great care must be taken when combining multiple data sets; while true, this statement is disingenuous. While I've no idea if the author's methods are correct or not, it's abundantly clear that they haven't just thrown everything together willy-nilly.

McGaugh et al. correctly note that the press release about the letter (http://perma.cc/JJ4S-G42D) makes very strong assertions (proof of dark matter) which are not at all warranted by the paper. It is not "direct observational proof" at all, it doesn't automatically falsify all alternatives. It is simply evidence which is compatible with the dark matter model - nothing more, nothing less. The paper is far more ambiguous as to whether it's claiming a really novel result or just improved evidence - the press release is unequivocal that it's a brand new result.
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