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.
Highlights
Since the discovery of the first quasar in 1963 (Schmidt, 1963), this type of extremely distant active galactic nuclei (AGN) has gradually become the focus of astronomical research
The Gaia celestial reference frame (Gaia-CRF3) is materialised by 1,614,173 quasars in GEAC (Brown et al, 2021), and we find that there are 111 common sources between GEAC and catalog A, and 16 common sources with Catalog B, which we recommend removing from GEAC
During the selection process, many spectroscopically identified quasars showed abnormal astrometric characteristics, such as significant parallaxes and large proper motions. These quasars may come with astrometric jitter detectable with Gaia data
Summary
Since the discovery of the first quasar in 1963 (Schmidt, 1963), this type of extremely distant active galactic nuclei (AGN) has gradually become the focus of astronomical research. The total number of identified quasars has exceeded one million, and these quasars have been collected and compiled into various catalogs (see, e.g., Véron-Cetty and Véron 2010; Souchay et al, 2019; Liao et al, 2019; Flesch 2021) Among these confirmed quasars, some spectroscopically identified quasars show abnormal astrometric characteristics in the Gaia high-precision astrometric observation (Wu et al, 2021). Some spectroscopically identified quasars show abnormal astrometric characteristics in the Gaia high-precision astrometric observation (Wu et al, 2021) These abnormal quasars have large proper motions or significant astrometric noises, which means that they are not suitable to be used to establish the celestial reference frame. Most of the known dual AGN are at low redshifts or have large physical separation ( > 20kpc), and only several known small-separation dual quasars are at high redshifts (Chen et al, 2022), while Gaia’s high-precision astrometric data has not been seriously considered
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