Is the "Manhattan Ant" a new species; still only found in Manhattan's Upper West Side?
Rob Dunn is a professor at North Carolina State University (though apparently taught at Columbia University at some point). I recall him mentioning this specific NY ant discovery to me 4-5 years ago. A better pop-sci article can be found here that suggests this discovery was circa 2012. Another related article can be found here.   

You can find a few other papers regarding urban ant populations by Dunn and collaborator Amy Savage and others via Rob Dunn's website, (Ex: Savage et al. 2014 and Penick et al. 2015).

However, I could not find evidence in the few relevant papers I skimmed for the the so-called "Manhattant" or evidence of any publications formally introducing this as a new species.  

Pećarević et al. 2010 ("Biodiversity on Broadway - Enigmatic Diversity of the Societies of Ants (Formicidae) on the Streets of New York City") lists a number of species found by Dunn and others in Manhattan, but again makes no mention of this specific discovery. 

My conclusion is that since Dunn has not listed this as one of his many publications on his website it's either burried in another paper as an ancillary artifact, or, more likely, has not been formally described...

You could reach out to Rob directly [email | twitter], I suppose, and update us all on this question!