AJo top pair facing 3 barrels OOP

this spot probably seems trivial to many of you. i'm going to ask anyway. villain is 21/16 with a 5% 3b over ~100. his ATS is 43% overall. he has cbet 4/4 flops, and 1/1 turns. i am comfortable flatting flop and turn because he is likely to have some worse Ax hands in his range for value, plus he could still conceivably be double-barreling some air or flush draws (not that i think that's a very good idea vs my range on this board). my question is regarding the river. do we expect him to go for three streets with AT? A8? his sizing, if anything, seems to suggest he is looking for value and is never just blindly 3-barreling some random shit. so does he attempt to value bet worse?

i would be quite comfortable folding this vs the 50nl FR regs i've encountered, but in 6m i'm not so sure of my reads. so call or fold?

PokerStars No-Limit Hold'em, $0.50 BB (6 handed) - PokerStars Converter Tool from FlopTurnRiver.com
UTG ($30)
MP ($52.35)
CO ($20)
Button ($51.50)
SB ($50.70)
Hero (BB) ($50.75)
Preflop: Hero is BB with A, J
3 folds, Button bets $1.50, 1 fold, Hero calls $1
Flop: ($3.25) 4, A, 9 (2 players)
Hero checks, Button bets $2, Hero calls $2
Turn: ($7.25) 5 (2 players)
Hero checks, Button bets $4.50, Hero calls $4.50
River: ($16.25) 5 (2 players)
Hero checks, Button bets $8, Hero?