On the redshift of the bright BL Lac object PKS 0048-097

TL;DR

This paper determines the redshift of the bright BL Lac object PKS 0048-097 using high-resolution spectroscopy, revealing its distance and enabling analysis of its optical beaming and high-energy absorption.

Contribution

The study provides the first spectroscopic redshift measurement of PKS 0048-097 using the X-Shooter instrument, combining high resolution and broad wavelength coverage.

Findings

Redshift of PKS 0048-097 is z=0.635.

Detection of a Mg II absorption system at z=0.154.

Implications for optical beaming and EBL absorption.

Abstract

Aims: The determination of elusive redshifts of bright BL Lac objects Methods: We use the capabilities of newly available spectrograph X-Shooter at European Southern Observatory (ESO) Very Large Telescope, that combines high resolution and a large wavelength range, to obtain UVB to near-IR spectra of BL Lacs. Results: Our observations of PKS 0048-097 detect three emission lines that permit to derive a redshift z = 0.635. Moreover, a Mg II absorption system at z = 0.154 that is associated with a foreground spiral galaxy at 50 Kpc projected distance is found. Conclusions: The obtained redshift allows us to comment about the optical beaming factor and the absorption of the high energy spectrum by the Extragalactic Background Light.