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Evolution of BL Lac host galaxies

Published online by Cambridge University Press:  01 December 2004

J. Heidt
Affiliation:
Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany
M. Tröller
Affiliation:
Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
K. Nilsson
Affiliation:
Tuorla Observatory, 21500 Piikkiö, Finland
K. Jäger
Affiliation:
Universitätssternwarte Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany
L. Takalo
Affiliation:
Tuorla Observatory, 21500 Piikkiö, Finland
R. Rekola
Affiliation:
Tuorla Observatory, 21500 Piikkiö, Finland
A. Sillanpää
Affiliation:
Tuorla Observatory, 21500 Piikkiö, Finland
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Abstract

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Deep, high-resolution I-band images of 24 BL Lac objects between z = 0.3 and 1.3 taken with the NOT and the ESO-NTT and VLT telescopes are discussed. In 17/24 (71%) of the BL Lac objects, we detected an underlying nebulosity, in 11/17 the host of the BL Lac in the redshift range z = 0.3-1 (< z > = 0.6). The host galaxies are luminous (MI = −25.2±0.8) and large (re = 10.5±7 kpc). They are on average about 0.6 mag brighter than BL Lac host galaxies at z ∼ 0.3 indicative of evolution, whereas their half-light radii are similar. By combining our data with literature data at low-redshift and applying evolutionary models to them, we find that the properties of the host galaxies of BL Lac objects up to z ∼ 1 are compatible with passively evolving elliptical galaxies formed at a redshift of z ≥ 2. Host galaxies of low-luminosity radio-loud AGN (BL Lac/FR I) have very similar properties to the hosts of radio-quiet QSOs and high-luminosity radio-loud AGN (radio-loud QSO/FR II) over a wide redshift range. This supports the picture of the “Grand Unification”, in which AGN activity is a transient phenomenon in galaxy evolution.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Type
POSTERS
Copyright
© 2004 International Astronomical Union