A Roxbury man pleaded not guilty today to charges that he raped and murdered a Dominican woman who had moved to Boston so her son could get medical care, prosecutors said. Eldrick D. Broom, 27, was free on personal recognizance at the time of the slaying after being charged with a different crime: beating up his pregnant girlfriend. Broom was arraigned today in Suffolk Superior Court on charges of aggravated rape and first-degree murder for the Nov. 21 killing of Rosanna Camilo inside her Fairlawn Avenue apartment, Suffolk District Attorney Daniel F. Conley’s office said. Clerk Magistrate Gary D. Wilson ordered Broom held without bail.