| Issue |
A&A
Volume 418, Number 3, May II 2004
|
|
|---|---|---|
| Page(s) | 813 - 825 | |
| Section | Extragalactic astronomy | |
| DOI | https://doi.org/10.1051/0004-6361:20034467 | |
| Published online | 16 April 2004 | |
Evolution of BL Lacertae host galaxies *,**,***
1
Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany
2
Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
3
Tuorla Observatory, 21500 Piikkiö, Finland
4
Universitätssternwarte Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany
Corresponding author: J. Heidt, jheidt@lsw.uni-heidelberg.de
Received:
7
October
2003
Accepted:
14
January
2004
We present and discuss deep, high-resolution I-band images of 24 BL Lac
objects between 
and 1.3 taken with the Nordic Optical
Telescope (NOT) and the ESO-NTT and VLT telescopes.
In addition, new redshifts for the BL Lac objects PKS 0406+121, PKS 0426–380
and PKS 1519–273 are reported.
In 17/24 (71%) of the BL Lac objects, we detected an
underlying nebulosity, in 11/17 for the first time. We assigned the underlying
nebulosity to the BL Lac host galaxy in 11 cases spanning the redshift range 
. The remaining 6 BL Lac objects have either intervening galaxies (S4
0218+35, PKS 0426–380), no redshift (MH 2133–449) or are probably
misidentified (Q 0230+3429, B2 0937+26, MS 2347.4+1924).
Restricting ourselves to the 11 BL Lac objects (
),
where a core and host galaxy was
detected, we find that their host galaxies are luminous (
)
and large (
kpc). They are on average about 0.6 mag brighter
than BL Lac host galaxies at 
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 show that the properties of the host galaxies
of BL Lac objects up to 
are compatible with passively evolving
elliptical galaxies formed at a redshift of 
(13 Gyrs ago in our adopted cosmology).
Our results, however, are affected by an unavoidable luminosity bias and need
to be confirmed. Future prospects are described.
If they could be confirmed, 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.
Key words: methods: data analysis / galaxies: active / galaxies: BL Lacertae objects: general / galaxies: evolution / galaxies: fundamental parameters / galaxies: photometry
Based on observations collected with the VLT-UT1 on Cerro Paranal (Chile), the NTT on La Silla (Chile) operated by the European Southern Observatory in the course of the observing proposals 64.P-0230 and 66.B-0125.
© ESO, 2004
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