I found this wire hanging below the vehicle, which I have since tied such that is not dangling. Does anyone know what it is?

Thanks!

edit: I have attached the image but I'm not sure if it is showing up.

 

O2 sensor harness. Looks like it has come out of brackets and clips that hold it in place.

 

Thanks. It turns out at around the same time that this fell CEL for P0420 came on. Do you think that this could be related? I know that P0420 can often have to do with O2 sensors.

 

Yes an O2 sensor issue can cause a P0420. The P0420 is for catalytic converter efficiency - which is measured by comparing the signals from the rear O2 sensor with the front sensor. Other causes are fuel trim issues (ie fuel pressure too high, wonky temp sensor), exhaust leak, bad cat converter. Considering your wire dropped down, you should check for an issue with the sensor associated with that wire...