Oregon Health & Science University and Portland-based Legacy Health hospital chain have submitted their long-awaited application for state approval of a proposed merger, launching a new phase of scrutiny for the proposed deal. Having announced the idea more than a year ago, the public research university and six-hospital nonprofit hospital system on Thursday submitted their application to the state office that reviews large healthcare transactions for potentially harmful effects on patients and employees. If the deal is approved, Legacy would become part of OHSU, making the combined hospital system a powerhouse in Oregon healthcare.