A galaxy with 2 names the reason is historical cataloging, not that they are truly two different galaxies. William Herschel initially recorded what he thought were two nearby nebulae in that area, and later the second entry was kept as NGC 2905 even though it is actually a bright knot or star-forming region within NGC 2903.

What happened

Herschel saw “two” objects very close together and described them as one extended system with two bright parts. When the New General Catalogue was compiled later, both positions got separate numbers, so the main galaxy became NGC 2903 and the nearby bright feature became NGC 2905.

In modern terms

Today, most references treat NGC 2905 as part of NGC 2903, not as a separate galaxy. So if you see NGC 2903 “also known as” NGC 2905, that is really shorthand for an old catalog confusion rather than a true alternate name.