Gaia Data Release 3: Astrophysical parameters inference system (Apsis) I -- methods and content overview

TL;DR

Gaia Data Release 3 provides an extensive, homogeneous set of astrophysical parameters derived from Gaia's spectra, astrometry, and photometry, covering billions of sources and numerous astrophysical properties.

Contribution

This paper introduces the Gaia DR3 astrophysical parameters inference system (Apsis) and details its methods and the comprehensive data products it generates from Gaia data.

Findings

Derived parameters for 1.6 billion objects including classification probabilities.

Produced distances, extinction maps, and redshifts for millions of sources.

Created the most extensive homogeneous astrophysical parameters database to date.

Abstract

Gaia Data Release 3 contains a wealth of new data products for the community. Astrophysical parameters are a major component of this release. They were produced by the Astrophysical parameters inference system (Apsis) within the Gaia Data Processing and Analysis Consortium. The aim of this paper is to describe the overall content of the astrophysical parameters in Gaia Data Release 3 and how they were produced. In Apsis we use the mean BP/RP and mean RVS spectra along with astrometry and photometry, and we derive the following parameters: source classification and probabilities for 1.6 billion objects, interstellar medium characterisation and distances for up to 470 million sources, including a 2D total Galactic extinction map, 6 million redshifts of quasar candidates and 1.4 million redshifts of galaxy candidates, along with an analysis of 50 million outlier sources through an unsupervised classification. The astrophysical parameters also include many stellar spectroscopic and evolutionary parameters for up to 470 million sources. These comprise Teff, logg, and m_h (470 million using BP/RP, 6 million using RVS), radius (470 million), mass (140 million), age (120 million), chemical abundances (up to 5 million), diffuse interstellar band analysis (0.5 million), activity indices (2 million), H-alpha equivalent widths (200 million), and further classification of spectral types (220 million) and emission-line stars (50 thousand). This catalogue is the most extensive homogeneous database of astrophysical parameters to date, and it is based uniquely on Gaia data.