Can I be sure that it is a spiral arm? No.
by Budgieye moderator
Can I be sure? No. The only way to be sure is to take a spectrum, which is expensive.
#Bright ringed_galaxy on the left.
But the galaxy is bright, as if it has undergone a recent merger, so I would expect bright areas of star formation and deformed spiral arms or #tidal_trails. If I expand the image using Ctrl+, I think I can see where an arm attaches. The "arc" is oval shaped, slightly flattened, since we are seeing the galaxy at a angle. Real arcs ignore our perspective, and are circle-shaped. The arc is bright white-blue, and I would expect it to be darker blue. There are greener areas of increased star formation and supernova explosions nearer the nucleus, though admittedly, not in the arc.