Name M51/NGC5194 Right Ascension 13h29.9m Declination +47 °12′ Type SAbcp B Magnitude 9.0 Distance 30 million light years Name M51/NGC5195 Right Ascension 13h30.0m Declination +47 °16′ Type SBpec B Magnitude 10.5 Distance 30 million light years

M51 is a spiral galaxy (Sbc type) in CVn. Since two galaxies with different sizes are connected, this is known as "The Galaxy with a Child" in Japan (In the Western world, it is known as the "Whirlpool Galaxy"). The larger one is NGC5194 and the smaller one is NGC5195. It is also known that the main core is active, and also classified into the Seyfert 2 type galaxy. M51は，りょうけん座にある渦巻銀河(Sbc型)ですが， 大小2つの銀河がつながっているため， “子持ち銀河”の名前で有名です． 大きい方がNGC5194，小さい方がNGC5195です． 距離はおよそ3000万光年になります． 中心核が活動性を示すことも知られていて， セイファート2型銀河にも分類されています． By courtesy of the Subaru Telescope / NAOJ

Optical Spectra of M51

NGC5194

NGC5194 is a spiral galaxy whose appearance is normal. However, emission lines of Hα and [NII] are visible in the spectrum of the main core of M51. Since these emission lines are seen in HII region, in M51 it turns out that star formation takes place actively now. Therefore, in spite of its normal appearance an intense activity has taken place in M51. M51(NGC5194)は見かけは普通の渦巻銀河です． M51の中心核のスペクトルには， 水素のスペクトル線Hαと１階電離窒素[NII]の輝線が見えています． これらの輝線は，星（とくに大質量星）が活発に生じている， いわゆる星形成領域の電離水素領域（HII領域）に起因しており， M51では現在も活発に星形成が起こっていることを意味しています． したがって，M51は見かけほど大人しい普通の銀河ではないのでしょう． By courtesy of T.T.Takeuchi, T.T.Ishii (Kyoto Univ.)

NGC5195

Emission line of two [NII] is visible in the spectrum of the main core of NGC5195. Moreover, Hα is an absorption line. It is supposed that this is the feature of the galaxy with starburst at ancient times. Moreover, the NaI D line has come out strongly unusually. This is the strength which cannot be explained only by the absorption line of the low temperature star (mainly K type giant star) in this galaxy. For the reason, someone supposes that the arm extended from NGC5194 is running along the NGC5195 front, and absorption of the stellar gas of the arm has overlapped. NGC5195の中心核のスペクトルには，2本の[NII]の輝線が見え， その間のHαは吸収線になっています． これは，かなり昔に爆発的な星の形成（スターバースト） を起こした銀河の特徴だとされています． また，中性ナトリウムNaI D線が異常に強く出ています． これは，この銀河の低温度星（主にK型巨星） の吸収線だけでは説明できない強さなので， M5194から伸びる腕がNGC5195の前を通っていて， その腕の星間ガスの吸収が重なっているため， という説があります． By courtesy of T.T.Takeuchi, T.T.Ishii (Kyoto Univ.)