SQUAB I: The first release of Strange QUasar candidates with ABnormal astrometric characteristics from Gaia EDR3 and SDSS

TL;DR

This paper introduces the first catalog of quasar candidates with abnormal astrometric features from Gaia EDR3 and SDSS, aiming to identify scientifically interesting objects like quasar pairs and lensed quasars.

Contribution

It presents a novel selection method for abnormal quasars using Gaia and SDSS data, resulting in two candidate catalogs of potential quasar pairs.

Findings

Two catalogs with 155 and 44 candidates respectively.

Potential identification of quasar pairs and lensed quasars.

New criteria for abnormal quasar selection from astrometric data.

Abstract

Given their extremely large distances and small apparent sizes, quasars are generally considered as objects with near-zero parallax and proper motion. However, some special quasars may have abnormal astrometric characteristics, such as quasar pairs, lensed quasars, AGNs with bright parsec-scale optical jets, which are scientifically interesting objects, such as binary black holes. These quasars may come with astrometric jitter detectable with Gaia data, or significant changes in the position at different wavelengths. In this work, we aim to find these quasar candidates from Gaia EDR3 astrometric data combining with Sloan Digital Sky Survey (SDSS) spectroscopic data to provide a candidate catalog to the science community. We propose a series of criteria for selecting abnormal quasars based on Gaia astrometric data. We obtain two catalogs containing 155 sources and 44 sources, respectively. They are potential candidates of quasar pairs.