Gaia Early Data Release 3: Summary of the contents and survey properties (2012.01533v2)

Abstract: We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (G_BP-G_RP) colour are also available. The passbands for G, G_BP, and G_RP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia-CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 percent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30--40 percent for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G, G_BP, and G_RP is valid over the entire magnitude and colour range, with no systematics above the 1 percent level.

• The paper advances astrometric precision by achieving a 30% improvement in parallax and a doubling of proper motion accuracy compared to previous data releases.
• The paper demonstrates photometric homogeneity by reducing systematic errors to below 1% across multiple bands using refined data processing techniques.
• The paper outlines innovative data processing methods by the DPAC, converting 1.8 billion transits into reliable solutions that set a new benchmark for future Gaia releases.

Overview of Gaia Early Data Release 3: Contents and Survey Properties

Gaia Early Data Release 3 (Gaia EDR3) marks a significant enhancement in the survey capabilities provided by the Gaia mission. It offers astrometry and photometry for approximately 1.8 billion celestial sources, all brighter than magnitude 21, and incorporates an updated list of radial velocities derived from the previous data release. This essay aims to dissect the components and improvements offered by Gaia EDR3, concentrating on astrometric and photometric advancements, notable results, and future implications for astronomical research.

Key Advancements in Gaia EDR3

1. Astrometric Precision and Accuracy: Gaia EDR3 offers substantial improvements over Gaia DR2 with a 30% increase in parallax precision and a twofold gain in proper motion precision. The systematic errors in astrometry have been further suppressed, with improvements of 30–40% for parallaxes and around 2.5 times for proper motions. Such enhancements herald new capabilities in probing the Galactic phase space with unprecedented precision.
2. Photometric Homogeneity: A notable advancement in Gaia EDR3 is the homogeneity of photometric measurements across different color and magnitude bands. This improvement mitigates systematic photometric errors to below 1%, and a uniform passband now suffices for photometry in the G, BP (G_BP), and RP (G_RP) bands.
3. Mechanics of Data Processing: The data released in Gaia EDR3 were processed using data from the initial 34 months of the Gaia mission. The Gaia Data Processing and Analysis Consortium (DPAC) handled the intricate task of converting over 1.8 billion transits into astrometric and photometric solutions, setting a new benchmark in data precision and reliability.

Scientific Results and Applications

The enhanced data quality of Gaia EDR3 has opened the door for numerous scientific investigations. For instance:

• Galactic Dynamics: The increased precision in proper motions facilitates detailed studies of the kinematics in the Galactic anticenter region. The data unveil intricate phase structures that increase our understanding of the Galactic disk dynamics.
• Local Star Surveys: The Gaia Catalogue of Nearby Stars provides an extensive characterisation of stars within 100 pc of the Sun, enhancing local stellar population studies.
• Extragalactic Research: Gaia EDR3 has improved the accuracy of the celestial reference frame (Gaia-CRF3), essential for aligning extragalactic surveys.

Challenges and Known Limitations

Despite these advancements, users should exercise caution regarding several limitations:

• Astrometric Systematics: Although reduced, systematic errors still exist in the parallaxes and proper motions, contingent upon source magnitude and color.
• Photometric Consistency: While overall improved, the photometry in crowded regions and for red faint sources may exhibit inaccuracies due to previous erroneous flux recordings.
• Radial Velocity Data: The included radial velocities are copied from Gaia DR2, further updates are anticipated in subsequent releases.

Future Prospects

Gaia EDR3 sets a solid foundation for future releases. The full Gaia Data Release 3, anticipated in 2022, will enrich these datasets with additional astrophysical parameters and new radial velocity measurements. The eventual releases, Gaia DR4 and DR5, could vastly improve the temporal baseline of the survey, enhancing the precision of dynamic measurements.

Conclusion

Gaia EDR3 represents a stride forward in precision astrometry and photometry, enhancing our ability to perform scientific investigations across multiple domains of astronomy. It underscores the crucial role of continuous data refinement and calibration in achieving unparalleled data quality. As Gaia approaches its potential mission end in 2025, each successive data release promises to further unravel the complexities of our galaxy and beyond.