) ▁exist ▁and ▁the ▁dust ▁content ▁can ▁be ▁extremely ▁high . ▁Three ▁S ▁class ified ▁galaxies ▁are ▁in ▁the ▁Atlas . ▁ ▁Active ▁galaxies ▁have ▁Active ▁Gal actic ▁N uc lei ▁( AG N ) ▁and ▁include ▁LIN ER , ▁Se y fert , ▁Radio ▁Gal axy , ▁Qu as ar ▁and ▁Bla zar ▁types . ▁' Activity ' ▁refers ▁to ▁non - stell ar ▁processes ▁occurr ing ▁or ▁origin ating ▁in ▁a ▁galax y ▁nucle us . ▁An ▁active ▁nucle us ▁has ▁a ▁spectrum ▁with ▁a ▁continu um ▁that ▁cannot ▁be ▁explained ▁by ▁radiation ▁from ▁one ▁or ▁more ▁stell ar ▁( or ▁black body ) ▁objects . ▁Ele ven ▁A ▁class ified ▁galaxies ▁are ▁in ▁the ▁Atlas . ▁Active ▁galaxies ▁typically ▁have ▁strong ▁emission ▁over ▁a ▁large ▁portion ▁of ▁the ▁elect romagnet ic ▁spectrum ▁making ▁them ▁prime ▁targets ▁for ▁multi w avel ength ▁observations . ▁Hence ▁galaxies ▁categor ised ▁Active ▁make ▁up ▁a ▁large ▁fraction ▁( 3 1 %) ▁of ▁the ▁Atlas ▁sample , ▁and ▁compr ise ▁ 4 3 % ▁of ▁the ▁total ▁sample ▁if ▁other ▁Atlas ▁galaxies ▁with ▁activity ▁as ▁a ▁sub - category ▁are ▁included . ▁ ▁Rad iation ▁from ▁all ▁regions ▁of ▁the ▁elect romagnet ic ▁spectrum ▁has ▁now ▁been ▁detected ▁from ▁galaxies . ▁These ▁observations ▁have ▁util ized ▁teles cop es ▁at ▁ground - based ▁observ ator ies ▁( many ▁located ▁at ▁high ▁alt itude ▁mountain ▁sites ), ▁teles cop es ▁in ▁aircraft ▁( ≥ 1 0   km ▁alt itude ), ▁detect ors ▁on ▁bal lo