Optical study of PKS B1322-110, the intra-hour variable radio source

TL;DR

This study combines radio and optical observations to identify PKS B1322-110 as a high-redshift flat-spectrum radio quasar, providing the first optical spectrum and insights into Galactic plasma emission.

Contribution

First optical spectrum of PKS B1322-110 confirming its nature as a high-redshift quasar and linking radio variability to optical properties.

Findings

PKS B1322-110 is a flat-spectrum radio quasar at z=3.007.

Detected Halpha emission likely from HeII at the quasar's redshift.

Set upper limits on Galactic plasma emission measure.

Abstract

Observations with the Australia Telescope Compact Array revealed intra-hour variations in the radio source PKS B1322-110 (Bignall et al. 2019). As part of an optical follow-up, we obtained Gemini Halpha and Halpha continuum (HalphaC) images of the PKS B1322-110 field. A robust 19-sigma detection of PKS B1322-110 in the Halpha-HalphaC image prompted us to obtain the first optical spectrum of PKS B1322-110. With the Gemini spectrum we determine that PKS B1322-110 is a flat-spectrum radio quasar at a redshift of z=3.007 +/- 0.002. The apparent flux detected in the Halpha filter is likely to originate from HeII emission redshifted precisely on the Galactic Halpha narrow-band filter. We set upper limits on the emission measure of the Galactic plasma, for various possible cloud geometries.