Andrew Left, an activist investor and well-known short seller, turned himself in to authorities in Los Angeles on Monday and is scheduled to appear before Judge Rozella A. Oliver in US District Court this afternoon. Mr. Left faces a criminal indictment issued by the Justice Department on Thursday and charges of "entrapment" tactics by the Securities Exchange Commission. Mr. Left, who lives in Florida, faces 19 criminal charges that could see him jailed if convicted. He is known for his disdain for the "irrationality" of thematic stocks such as GameStop, with the indictment saying he "took trading positions contrary to his publicly published and publicized trading positions" and that he "misrepresented his trading positions during public appearances on news programs."