The nature of the SDSS galaxies in various classes based on morphology, colour and spectral features - II. Multi-wavelength properties

摘要

We present a multi-wavelength study of the nature of the SDSS galaxiesdivided into fine classes based on their morphology, colour and spectralfeatures. The SDSS galaxies are classified into early-type and late-type; redand blue; passive, HII, Seyfert and LINER, which returns a total of 16 fineclasses of galaxies. The properties of galaxies in each fine class areinvestigated from radio to X-ray, using 2MASS, IRAS, FIRST, NVSS, GALEX andROSAT data. The UV - optical - NIR colours of blue early-type galaxies (BEGs)seem to result from the combination of old stellar population and recent starformation (SF). Non-passive red early-type galaxies (REGs) have largermetallicity and younger age than passive REGs, which implies that non-passiveREGs have suffered recent SF adding young and metal-rich stars to them. Theradio detection fraction of REGs strongly depends on their optical absolutemagnitudes, while that of most late-type galaxies does not, implying thedifference in their radio sources: AGN and SF. The UV - optical colours and theradio detection fraction of passive RLGs show that they have properties similarto REGs rather than non-passive RLGs. Dust extinction may not be a dominantfactor making RLGs red, because RLGs are detected in the mid- and far-infraredbands less efficiently than blue late-type galaxies (BLGs). The passive BLGshave very blue UV - optical - NIR colours, implying either recent SF quenchingor current SF in their outskirts. Including star formation rate, othermulti-wavelength properties in each fine class are investigated, and theirimplication on the identity of each fine class is discussed (abridged).