▁The ▁galaxies ▁are ▁divided ▁into ▁categories ▁of ▁Normal ▁( N ), ▁Inter act ing ▁( I ), ▁Mer ging ▁( M ), ▁Star bur st ▁( S ) ▁and ▁Active ▁( A ), ▁though ▁many ▁have ▁been ▁class ified ▁across ▁one ▁or ▁more ▁categories . ▁The ▁reasons ▁for ▁inclusion ▁of ▁a ▁galax y ▁into ▁a ▁specific ▁category ▁is ▁explained ▁in ▁the ▁individual ▁galax y ▁summar ies ▁in ▁the ▁Atlas . ▁ ▁Gal axy ▁types ▁ ▁Normal ▁galaxies ▁include ▁galaxies ▁that ▁appear ▁morph olog ically ▁normal , ▁do ▁not ▁possess ▁unusual ▁star ▁formation ▁rates , ▁and ▁have ▁continu um ▁spect ra ▁with ▁a ▁thermal ▁( stell ar ) ▁form ▁character ized ▁by ▁one ▁or ▁more ▁temper atures . ▁Tw elve ▁N ▁class ified ▁galaxies ▁are ▁in ▁the ▁Atlas . ▁ ▁Inter act ing ▁galaxies ▁display ▁morph ological ▁sign atures ▁of ▁a ▁gravit ational ▁interaction ▁with ▁another ▁nearby ▁galax y ▁or ▁are ▁influenced ▁by ▁the ▁passage ▁through ▁a ▁dense ▁medium ▁that ▁can ▁' strip ▁out ' ▁constitu ent ▁gas . ▁Four ▁I ▁class ified ▁galaxies ▁are ▁in ▁the ▁Atlas . ▁ ▁Mer ging ▁galaxies ▁are ▁the ▁later ▁evolution ary ▁stages ▁of ▁two ▁or ▁more ▁Inter act ing ▁galaxies ▁that ▁have ▁or bits ▁and ▁dynamics ▁condu ci ve ▁to ▁a ▁final ▁mer ger . ▁Five ▁M ▁class ified ▁galaxies ▁are ▁in ▁the ▁Atlas . ▁ ▁Star bur st ▁galaxies ▁under go ▁inten se ▁star ▁formation ▁that ▁is ▁well ▁in ▁excess ▁of ▁normal ▁rates . ▁Lar ge ▁numbers ▁of ▁young ▁stars ▁( O ▁and ▁B ▁spectral ▁type