Issue |
A&A
Volume 406, Number 2, August I 2003
|
|
---|---|---|
Page(s) | 565 - 577 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20030804 | |
Published online | 17 November 2003 |
PKS 0537-441: Extended [O II] emission and a binary QSO?*
1
Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany
2
Universitätssternwarte Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany
3
Tuorla Observatory, 21500 Piikkiö, Finland
4
Universitätssternwarte München, Scheinerstr. 1, 81679 München, Germany
5
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
6
Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
Corresponding author: J. Heidt, jheidt@lsw.uni-heidelberg.de
Received:
25
March
2003
Accepted:
19
May
2003
We present high-resolution imaging and low-resolution
spectroscopy of the BL Lac object
PKS 0537-441 () and its environment carried out with the
ESO-NTT and VLT telescopes. The observations were
designed to clarify, whether the properties of PKS 0537-441 are affected by
gravitational microlensing due to the claimed detection of a galaxy
along the line-of-sight to the BL Lac, or whether PKS 0537-441 and its environment
act as a lensing system itself, as suggested by the detection of
several closeby
companion galaxies with similar morphologies close to PKS 0537-441.
Our observations show that neither case seems to be likely. Within our
images we did not find a galaxy along the line-of-sight
to the BL Lac as claimed
previously.
In addition, our spectroscopy shows that none of the four closest
companion galaxies
(including one new detection by us)
is at high redshift. Instead, two of the four nearby
companion galaxies to PKS 0537-441 are within 200 km s-1 of the systemic
velocity of the BL Lac (
and 0.895, respectively).
The third companion galaxy is at higher redshift (
).
The fourth companion galaxy shows evidence of Mg II absorption
redwards of its systemic velocity and is perhaps a mini
low-ionization BAL QSO at
.
If the latter can be confirmed, PKS 0537-441 is the
first BL Lacertae object being a member of a binary Quasar.
While we do not find (micro)lensing effects important for
this source or its environment, our observations revealed a
highly interesting feature. We detected extended [O II] emission in the
off-nuclear spectrum of PKS 0537-441, which is most likely due to
photoionization from the active nucleus, although we can not rule out
the possibility that the extended emission is due to jet-cloud
interaction with the counterjet of PKS 0537-441.
According to our analysis of the photometric data,
PKS 0537-441 seems to be located in a cluster environment as rich as Abell
type 0-1. This is supported by the detection of four galaxies in the
field with similar redshifts as the BL Lac (
).
However, we
serendipitously found even more galaxies at somewhat higher redshifts (
). Thus, PKS 0537-441 might be located in front of a galaxy
cluster at somewhat higher redshift or even be part of a large-scale
structure with an extension towards the BL Lac.
Key words: methods: data analysis / galaxies: distances and redshift / galaxies: active / galaxies: BL Lacertae objects: individual: PKS 0537-441 / quasars: emission lines
© ESO, 2003
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