On the nature of the blue light in central cluster galaxies

Abstract

An excess blue component of light, extended over the innermost few kpc, is observed in several central cluster galaxies. Using a combination of blue optical spectra and IUE data, we show that the spectrum of the excess blue light is consistent with both star formation dominated by the light of B5 stars, and power-law spectra with slopes between λ −1.5 and λ −2.5 , even allowing for intrinsic reddening. If the blue continuum is emitted by stars, we find that the data are more consistent with a fading starburst model than with continuous star formation. We compare possible origins for the blue continuum, such as the scattering of a hidden active nucleus, or a starburst induced by either the radio jets or a subcluster merger