I don't like your raise preflop here, with everyone just calling you could easily be behind a bigger ace. A9 suited is early position is not a great hand.
If you are certain your opponent has a flush on the turn you HAVE TO FOLD. I know its only for 840 more chips and there is ~4000 in the pot. You are only getting ~ 5:1 pots odds
for this call. Against a made hand like a flush you are drawing to four outs (two aces and two nines) so you have a 4/45 or ~9% chance of hitting your outs, which justify a fold here (If pot odds
are not equal to or better than odds of hitting your hand, do NOT call).
This opponent seemed to play the hand like he had a flush draw. This tournament was probably a freeroll...therefore it is pretty easy to put him on a flush here.
In a more competetive environment I would call this bet since you are pot committed if you are UNSURE of what your opponent has.
The only reason I say fold in your certain circumstance is because it is blatantly obvious that your opponent has hit his flush and there is no point putting more chips in with so few outs.