I think folding is better. He has some unpaired hands and maybe some 88 / 77 but he also might have some TT+. This looks a lot like AK, but even if it is AK/AQ etc. Against broadway 99 has 55%, against other pairs you are 20% .... it is costing you 2.39 into 5.15 less rake so you need 46% .... So from this you can work out he needs to have pairs only x% of the time...

80*.55 + 20*.22 = ~ 48%... so villain needs to have unpaired overs 80% of the time. Put these into a range calc software like pokerstove or something similar. Give him TT+ then see how many different combinations of overcards he needs to make it a 4:1 ratio of overs to pairs. I think you will find he needs to be as wide as hands like KJ / QJ which he likely isn't.

when we look at ranges this is probably a fold however I am just never open folding 99 vs a 50bb shove who I imagine is a fish

Fold.

For half a stack with so little dead money in the pot I would still be calling off a tight range. Do the EV calculations against a selection of ranges. You need him to be showing up with all kind of small pairs and suited connectors lower than a 9.

Personally I actually fold 99 here. I don't think it's a easy call. But I'm not saying I haven't got in 99 before PF vs large relative stacks than this, I have but only when I see the guy shoving PF regularly. Outside of that I still stick pretty close to my normal call off range, maybe JJ I add in if he seems pretty fishy as they often show up with smaller pairs after playing this way.