Holdem No Limit - $0.5 BB

SB ($129.27)
BB ($21.88)
UTG ($20.11)
MP ($9.25)
CO ($196.22)
Button ($113.87) [Hero]

Hero is Button with A, A
Preflop: (6 players, $0.75)
UTG calls $0.50, MP folds, CO calls $0.50, Hero calls $0.50 and raises $2.75, 2 folds, UTG calls $2.75, CO calls $2.75

Flop: 3, 3, 5 (3 players, $10.5)
UTG checks, CO bets $4, Hero calls $4 and raises $9, UTG folds, CO calls $9

Turn: 4 (2 players, $36.5)
CO checks, Hero ???

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Villian is an unknown.

What's your move on the turn, and why?