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Blue colours of BL Lac host galaxies

J. K. Kotilainen·R. Falomo
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Abstract

Near-infrared and optical imaging of BL Lac host galaxies is used to investigate their colour properties. We find that the R-H colour and colour gradient distributions of the BL Lac hosts are much wider than those for normal ellipticals, and many objects have very blue hosts and/or steep colour gradients. The blue colours are most likely caused by recent star formation. The lack of obvious signs of interaction may, however, require a significant time delay between the interaction event with associated star formation episodes and the onset of the nuclear activity.

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J. K. Kotilainen, R. Falomo. 2004-04-20. Blue colours of BL Lac host galaxies. https://doi.org/10.1017/s1743921304003138

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