"Using the Mayall Telescope at Kitt Peak and the DEIMOS spectrograph on the the Keck II Telescope in Hawaii, the researchers found previously unseen red giant stars out to a distance of at least 500,000 light years from Andromeda's center.
The researchers picked out Andromeda's faint halo stars using a technique developed by Karoline Gilbert, a UCSC graduate student, which distinguishes the halo stars from the more numerous foreground stars in our Milky Way."
Then I don't get the implication you see for the cosmological constant.