CHICAGO—Gunfire erupted at a party on Chicago’s South Side early Sunday, killing two people and wounding 13 others, authorities said. Officers responded at around 4:40 a.m., police spokesman Jose Jara said in a statement. Those shot were between the ages of 20 to 44. Jara earlier said 12 people had been shot, but police later raised the figure to 15. Seven of the wounded were taken to hospitals in serious to critical condition, fire department spokesman Larry Merritt told the Chicago Sun-Times. Speaking to reporters near the scene of the shooting in Chicago’s Park Manor neighborhood, Police Superintendent David Brown said investigators were still seeking a possible motive. Brown said four guns were recovered at the scene, but he didn’t say whether investigators believe more than one person fired shots. No arrests had been made. “We have a lot of work to do,” Brown said. “Detectives are really just getting …