Yea, I think you have to bet it out. In an unraised pot it's very likely that any ace will think he's good. Additionally you don't want a hand like q/10 or k/q picking up a free gut shot as project pointed out. Really though even on a board like a/9/4 I still bet it out there. Any ace screams to me that anyone with a/9+ is going to lose some money in these lower limits to you. No one flopped anything with you in this hand to contend it. Well played just hope someone flops second best next time