Low Frequency Two Meter Sky Survey Radial Artifacts Identified as BL Quasars

TL;DR

This study identifies radial artifacts in LOFAR radio images as emissions from Type 1 broadline quasars, linking calibration errors to specific astrophysical sources and improving artifact understanding.

Contribution

The paper demonstrates that certain radial artifacts in LOFAR images are caused by emissions from Type 1 BL quasars, providing a new interpretation of these calibration artifacts.

Findings

Radial artifacts are associated with BL quasars.

Artifacts are linked to broad emission lines like CIII and MgII.

Calibration errors may be influenced by quasar emissions.

Abstract

Through the use of a High Band Antenna system, the Low Frequency Array Two-Meter Sky Survey (LoTSS) is an attempt to complete a high-resolution survey of the northern celestial sky. To date, thousands of radio sources have been classified by LOFAR with most of them consisting of active galactic nuclei (AGN). The strong AGN emissions detected by LoTSS, it is thought, are powered by supermassive black holes (SMBHs) at the center of galaxies. During an analysis of 1500 images of these AGNs, we identified 10 radio sources with radial spokes emitted from an unknown source. According to LOFAR, the radial spokes are artifacts due to calibration errors with no origin, and therefore they cannot be associated with an optical source. Our preliminary hypothesis for the artifacts was that they were produced by ionized jets emitted from quasi-stellar objects (QSOs). Specifically, that strong emissions from Type 1 broadline (BL) quasars were directed in the line of sight of the observer (i.e., LOFAR) and as a result produced the image artifacts. To test our hypotheses, we cross-referenced the ra and dec coordinates of the artifacts with the galactic coordinates indexed in the Sloan Digital Sky Survey (SDSS) and confirmed that the artifacts were associated with BL QSOs. Further analysis of the QSOs, moreover, demonstrated they exhibited prominent broad emission lines such as CIII and MgII, which are characteristic of Type 1 BL quasars. It is our interpretation, therefore, that the radial spokes characterized as artifacts by LOFAR were produced by the emission of Type 1 BL quasars in the line of sight of the radio telescope.