Self-defense using bow and arrows?

Say, you want to defend yourself from an impending attack. You did not want to use firearms to prevent alerting the other possible attackers, so you decided to use a bow and broad-heads.

What is the MINIMUM draw-weight required for broad-head to pass through a human breastbone? Human/zombie skull?

Thanks.
Update: Update # 1: I did not mean to imply that the bows and broad-heads will be use alone. The ARs, shotguns and handguns will, of course, be available and accessible once stealth is no longer present.
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