PKS 0537-441: extended [O II] emission and a binary QSO?

Abstract

We present high-resolution imaging and low-resolution spectroscopy of the BL Lac object PKS 0537-441 (z = 0.893) and its environment. The observations were designed to clarify, whether the properties of PKS 0537-441 are affected by gravitational microlensing, or whether PKS 0537-441 and its environment act as a lensing system itself. Our observations show that neither case seems to be likely. We did not find a galaxy along the line-of-sight to the BL Lac as claimed previously, our spectroscopy shows that none of the four closest companion galaxies is at high redshift. Two of the four nearby companion galaxies to PKS 0537-441 are within 200 km/s of the systemic velocity of the BL Lac (z = 0.892 and 0.895, respectively). The third companion galaxy is at higher redshift (z = 0.947). 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 z = 0.885. If the latter can be confirmed, PKS 0537-441 is the first BL Lacertae object being a member of a binary Quasar. We also detected extended [O II] emission in the off-nuclear spectrum of PKS 05371-441, which is most likely due to photoionization from the active nucleus. Alternatively, the extended [O II] emission is due to jet-cloud interaction with the counterjet of PKS 0537-441. Our clustering analysis indicates that PKS 0537-441 is 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 (Delta z < 0.002). We found serendipitously even more galaxies at somewhat higher redshifts (z = 0.9-1). Thus, PKS0537-441 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.

13 pages, 9 figures, accepted for publication in A&A

References in corpus (16)

• Unified Schemes for Radio-Loud Active Galactic Nuclei
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• Unusual Broad Absorption Line Quasars from the Sloan Digital Sky Survey
• The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies
• The Properties of the Radio-Selected 1Jy Sample of BL Lacertae Objects
• The FORS Deep Field: Field selection, photometric observations and photometric catalog
• Extended radio emission in BL Lac objects - I: the images
• Binary quasars
• Clustering of galaxies around radio quasars at 0.5 < z < 0.8
• A uniform analysis of the Lyman alpha forest at z = 0-5: III. HST FOS Spectral Atlas
• LBQS 0103-2753: A 0.3 Arcsec Binary Quasar
• The HST Survey of BL Lac Objects: Gravitational Lens Candidates and Other Unusual Sources
• The evidence for jet-cloud interactions in a sample of high/intermediate-redshift radio galaxies
• Broad-band continuum and line emission of the gamma-ray blazar PKS 0537-441
• Discovery of an Optical Jet in the BL Lac Object 3C 371
• An Investigation of Gravitational Lensing in the Southern BL Lac PKS 0537-441

Cited by in corpus (2)

• Long-term monitoring of PKS 0537-441 with Fermi-LAT and multiwavelength observations
• The nature of close companions of the BL Lac Objects 1ES 0502+675 and 1ES 1440+122