what part is that on top of the roof.? it looks like a shark fin? on 2012 Buick LaCrosse

my wife was backing out of the garage and didn't allow the door to fully go up. The bottom of the door hit that "little shark fin thing" and raised it up about 1/2 inch. What is the name of that piece and is it inexpensive to repair?

Asked by for the 2012 Buick LaCrosse
the thing that gives radio reception begins with an A.
1 more answer
I did the same thing. I had to ask my husband if he posted this and he said no. I've been looking myself and this is the best I can come up with I don't know if it's correct or not?BASE. RADIO ANTENNA,RTO ANT (Assembly, Base or Module)? 001,(REPLACES ALL COLORS, PAINT TO MATCH)(ACDelco #25938474). Required: 01 For: GB,GM (EXC DIGITAL S-BAND AUDIO SYS(U2K) (2010-2010) (2010 - 2010). $69.88 / $47.17 Part # 25938474.
If this is correct can you let me know?