Weeks after the closing of Talbots at Westfield Montgomery mall, sister stores Ann Taylor and Soma have unexpectedly followed suit. Ann Taylor, which always appeared busy, will close this weekend after more than two decades at the mall. Soma went dark this week. The simultaneous closings are no coincidence: All three chains are owned by Sycamore Partners, a private equity firm that’s been buying up major retailers and closing a bunch of locations. At Westfield Montgomery, managers of all three stores told us that sales had been relatively strong and the sudden closings came as a shock. The nearest Ann Taylor is now a Factory store on Rockville Pike, which replaced Lane Bryant last winter.