I’m investing in the US market from Brazil. Should I be filling any reports or tax papers for the US authorities?

I'm using 2 brokerages based on the US. I sent money trough exchanges directly to my brokers account. I do not have US citizenship and I never set foot on US.

As far as I know the tax payments are automatically deducted from my dividends by the brokerages.

Still, is there any obligation a person like me has towards the American authorities?