Hero's preflop raise with AQo from the BB against a limping SB is standard and correct. Calling the SB's 19 BB all-in shove is also correct — AQo has strong equity against a limp-shove range and the pot odds are favorable.
Street-by-Street Analysis
Preflop (8/10)
Raising to 4,000 (4 BB) over the SB's limp is textbook with AQo — you're in position postflop and want to punish a weak limping range. When SB limp-shoves for ~19 BB effective, you're getting excellent odds to call: you need to put in 15,000 more into a pot that will be ~41,500 (including antes). AQo plays well against a limp-shove range that includes medium pairs, suited aces, and broadways. The call is clear. The only minor note: a slightly larger raise (4.5-5 BB) could extract more from the SB's wide limping range, but 4 BB is fine.
Hindsight: SB had A♦A♣ — the top of any limp-shove range. AQo is dominated here (~7% equity), but this is a cooler. Against the full range of hands that limp-shove for 19 BB, calling remains profitable.
