deciding to make a move on pot

I'm beginning to play some online multi-table tournaments. I feel I have pretty good beginning strategy and a good sense of when play tightens/loosens. I'm still, however, having difficulty making moves and opening up my play. Below is a play I made and would love some second opinions.

Party poker freeroll. I had ~6k, I think average was about 8k for tournament. Play was becoming more tight/aggressive, blinds were 150/300 but we were 1 min from break. UTG, 1600 stack, limped. 2nd player, ~10K limped. Folded to me in late position with A2. I see 1050 in pot and figure that if I put UTG all in he didn't have a good enough hand to call. No read on the individual player, just reasoning an ace or pair big enough to call would have warrented bringing in for a raise.

I raise to put UTG all in, blinds fold, UTG calls, 2nd limper folds. UTG showed A9.

Afterwards I'm thinking my read on the situation was pretty accurate but I still don't know if my play was good or if I needed more than just A2.

I'm also interested in knowing what hands UTG would be correct to call there. I'm now thinking he would have had to call a lot more hands than I originally thought, considering he would have been left with just 1300 and having to post blinds.