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تسجيل

Abnormal galaxies

المؤلف:  James Binney and Michael Merrifield

المصدر:  GALACTIC ASTRONOMY

الجزء والصفحة:  P-241

2026-09-08

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One goal of any classification scheme is to discover which galaxies are abnormal and therefore merit further investigation. The Hubble classification system and its modifications and derivatives refer principally to normal galaxies - Hubble labeled all abnormal galaxies as Type II Irregulars (Irr II galaxies)...

There are broadly two very different ways in which a galaxy can stand out from the crowd and be classified as 'abnormal': (i) it can have an unusual spectral distribution, such as being anomalously powerful at radio wavelengths, or showing strong, broad optical emission lines; (ii) it can look 'funny' in optical images perhaps by having a patchy, irregular brightness distribution, displaying a long luminous structure of some sort, or by possessing an anomalously bright nucleus. We shall find that funny-looking galaxies frequently have abnormal spectra, so studies of abnormal galaxies frequently focus on the same objects irrespective of whether their starting point is spectroscopy or imaging.