A321 First Officer reported a smoke alarm for the aft avionics panel while taxiing and a return to the gate.

Narrative

Besides a slight delay due to the aircraft not being towed into the gate everything went normal from the boarding process to the pushback and taxi out. As we got taxi instructions and started taxing to runway XXL ground asked if we can accept XXL at Taxiway 1; we ran the numbers and replied that we can do it; also at the same time we realized we might be departing quicker than expected and started the 2nd engine. After running through all our flows and checklists right after I made the PA for the flight attendants to be seated we heard some kind of alarm (beeping noise) unsure of where it was coming from for a second; I looked up and saw the red smoke indication on the Aft Avionics smoke panel; as soon as I saw it I verbalized it and the Captain immediately reached over and pressed the power button on the aft avionics switch shutting the system down which got rid of the alarm and smoke indication. The Captain called the cabin crew and they said they also had an indication and they would ask the other cabin crew if they smelled anything and would call us back. I notified ATC that we have an issue and cannot take the runway at the moment; they gave us a place to park at which point the Captain contacted maintenance over the radio. They advised us to contact Maintenance Control. While the Captain was getting in contact with Maintenance Control I made a PA to the passengers and one of the cabin crew members called us and said she did smell a bit of an electric smoke odor as if from an electrical spark. I called operations and let them know that we need to coordinate a gate for us to come back. Maintenance Control advised us to go back to the gate just as we planned. Once the Captain was off the phone with Maintenance Control I notified operations and ATC that we are going back to the gate. We taxied back to gate XXX and deplaned the aircraft. Neither I nor the Captain noticed any odor in the flight deck. Our only indication was the alarm and smoke light on aft avionics panel.