Searching for substellar companion candidates with <i>Gaia</i>

Context . In a previous paper, we introduced a new tool called – Gaia DR3 proper motion anomaly and astrometric noise excess–, or GaiaPMEX. This tool characterizes the mass and semi-major axis relative to the central star (sma) of a possible companion around any source observed with Gaia using the value of renormalized unit weight error ( ruwe ), or with both Gaia and H ipparcos using the value of the proper motion anomaly (PMa), either alone or combined with the ruwe . Aims . Our goal is to exploit the large volume of sources in the third Gaia data release catalog to find new exoplanet candidates. We wish to create a new input catalog of planet-candidate-hosting systems to enable future follow-up projects. Beyond magnitude 14, this catalog would prepare the arrival of powerful instruments on the Extremely Large Telescopes, which could include radial velocity (RV) follow-up of faint stars and direct imaging of planets around main sequence stars of gigayear ages. Methods . We used the mass-sma degenerate set of solutions obtained by GaiaPMEX from any value of ruwe to select a sample of bright ( G &lt; 16) Gaia sources whose companions could be in the planetary domain, with a mass of &lt;13.5 M J . We selected sources whose astrometric signature determined from the ruwe is larger than zero with a significance of &gt;2.7− σ ( p -value &lt;0.00694). Results . It led us to identify a sample of 9,698 planet-candidate-hosting sources that have a companion with a mass of possibly &lt;13.5 M J and a sma in the range of ∼1−3 au. We cross-matched our catalog with the NASA Exoplanet Archive (NEA) catalog of exoplanets, identifing 19 of our systems therein. We successfully detected eight confirmed substellar companions with an sma of 1–3 au, initially discovered and characterized with RV and astrometry. Moreover, we found six transiting-planet systems and two wide-orbit systems for whom, with GaiaPMEX, we predict the existence of supplementary companions. Focusing on the subsample of sources observed with H ipparcos , combining the constraints from ruwe and PMa, we confirm the identification of four new planetary candidate systems, HD 187129, HD 81697, CD-42 883, and HD 105330. Conclusions . Given the degeneracy of mass-sma, many of the candidates in this catalog of 9698 sources might have a larger mass in the brown-dwarf and stellar domain if their sma departs from the 1–3-au range. The vetting of this large catalog will be the subject of future studies.