Ca depletion and the presence of dust in large scale nebulosities in radiogalaxies (II)

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We investigate here the origin of the gas observed in extended emission line regions surrounding AGNs. We use the technique of calcium depletion as a test to prove or disprove the existence of dust in such a gas in order to discriminate between two main theories: (1) a cooling process from a hotter X-ray emitting phase surrounding the galaxy, (2) merging or tidal interaction between two or more components. We have obtained long slit spectroscopy of a sample of objects representative of different galaxy types although our main interest focus on radio galaxies. The spectral range was set to always includethe [CaII]λλ7291,7324 doublet. The faintness or absence of such lines is interpreted as due to the depletion of calcium onto the dust grains and, therefore, is a proof of the existence of dust mixed with the gas in the EELRs.