Gaia Early Data Release 3

Overview of the contents of Gaia Early Data Release 3. Image credit: ESA/Gaia/DPAC. Image license: CC BY-SA 3.0 IGO. Acknowledgement: Image was created by Sarah Poletti.

Information about the Gaia Early Data Release 3 (Gaia EDR3) is maintained at https://www.cosmos.esa.int/web/gaia/earlydr3 . Gaia EDR3 was published on 3 December 2020 at 12:00 CET. Gaia EDR3 delivers improved astrometry, with significantly improved parallaxes and proper motions, and mean photometry. The parallax improvement is typically 20% with respect to Gaia DR2, and the proper motions are typically a factor two better than in Gaia DR2.

Examples of some applications of Gaia Early Data Release 3 data are described in "Gaia Early Data Release 3 science" section.

Gaia Early Data Release 3 in numbers

Contents of Gaia EDR3

• The full five-parameter astrometric solution - positions on the sky (α, δ), parallaxes, and proper motions - for around 1.468 billion (1.468 x 10⁹) sources, with a limiting magnitude of about G ≈ 21 and a bright limit of about G ≈ 3. The astrometric solution wil be accompanied with some new quality indicators, like RUWE, and source image descriptors.
•     The full astrometric solution has been done as 5-parameter solution for 585 million sources and as 6-parameter solution for 882 million sources. In the 6-parameter solution, the additional fitted quantity is the so-called pseudo-colour that had to be included for sources without high-quality colour information.
•     In addition, two-parameters solutions - positions on the sky (α, δ) - for around 344 million additional sources.
•     G magnitudes for around 1.806 billion sources.
•     G _BP  and G_RP magnit udes for around 1.542 billion and 1.555 billion sources, respectively.
•     Please be aware that the photometric system for the G, G_BP, and G_RP bands in Gaia EDR3 is different from the photometric system as used in Gaia DR2 and Gaia DR1.
•     Full passband definitions for G, G_BP, and G_RP. More information will become available on Gaia EDR3 page on ESA website.
•     About 1.614 million celestial reference frame (Gaia-CRF) sources.
•     Cross-matches between Gaia EDR3 sources on the one hand and Hipparcos-2, Tycho-2 + TDSC merged, 2MASS PSC (merged with 2MASX), SDSS DR13, Pan-STARRS1 DR1, SkyMapper DR1, GSC 2.3, APASS DR9, RAVE DR5, allWISE, and URAT-1 data on the other hand.
•     Additionally, a Gaia DR2 to Gaia EDR3 match table.
•     Simulated data from Gaia Object Generator (GOG) and Gaia Universe Model Snapshot (GUMS) will be provided.
•     The commanded scan law covering the Gaia EDR3 data collection period will be provided. Also the major periods where data was not sent to the ground or could not be processed are identified.

To ease the use of the data, the Gaia EDR3 table in the Gaia Archive will be complemented with a set of (cleaned) Gaia DR2 radial velocities.

Background of the data

Gaia DR3 data (both Gaia EDR3 and the full Gaia DR3) are based on data collected between 25 July 2014 (10:30 UTC) and 28 May 2017 (08:44 UTC), spanning a period of 34 months. As a comparison, Gaia DR2 was based on 22 months of data and Gaia DR1 was based on observations collected during the first 14 months of Gaia's routine operational phase.
The reference epoch for Gaia DR3 (both Gaia EDR3 and the full Gaia DR3) is 2016.0. Remember that the reference epoch is different for each Gaia data release (it was was J2015.5 for Gaia DR2 and J2015.0 for Gaia DR1).
Positions and proper motions are referred to the ICRS, to which the optical reference frame defined by Gaia EDR3 is aligned. The time coordinate for Gaia EDR3 is the barycentric coordinate time (TCB).

Gaia Source Identifiers

Sources in the Gaia Catalogue are uniquely identified through the Gaia Source Identifier, i.e., the source_id field in the various tables in the Gaia Archive. The construction of the source identifiers is explained in the Archive documentation (for Gaia DR1, see the data model section). In particular the source_id number contains rough information about the source position on the sky.

As explained in previous announcements, there are various reasons why the identifier of a specific source may change or disappear when going from the Gaia DR1 to the Gaia DR2 source list and on to the Gaia EDR3 source list. Users of Gaia data should thus be aware that the source list for Gaia EDR3 should be treated as independent from Gaia DR2 and from Gaia DR1.
The Gaia source names for EDR3 will all be constructed as follows:

Gaia EDR3 yyy....yy

A table to trace sources from Gaia DR2 to Gaia EDR3 will be provided given that source identifiers used in Gaia DR2 may have changed or disappeared in Gaia EDR3. With each new data release, the source list is becoming progressively more stable and from Gaia DR2 to Gaia EDR3 changes impact less than 5% of the sources.

Performance and limitations of Gaia EDR3

Survey completeness

•     The Gaia EDR3 catalogue is essentially complete between G=12 and G=17. The source list for the release is incomplete at the bright end and has an ill-defined faint magnitude limit, which depends on celestial position.
•     The combination of the Gaia scan law coverage and the filtering on data quality which has been done prior to the publication of Gaia EDR3, does lead to some regions of the sky displaying source density fluctuations that reflect the scan law pattern. In addition, small gaps exist in the source distribution, for instance close to bright stars.

Astrometry

•     The uncertainties for the 6-parameter solutions are slightly worse than for 5-parameter solutions presented below. The 2-parameter solution (position only) uncertainties are 1-3 mas.
•     The position uncertainties are 0.01-0.02 mas for G<15, 0.05 mas at G=17, 0.4 mas at G=20, and 1.0 mas at G=21 mag.
•     The parallax uncertainties are 0.02-0.03 mas for G<15, 0.07 mas at G=17, 0.5 mas at G=20, and 1.3 mas at G=21 mag.
•     The proper motion uncertainties are 0.02-0.03 mas/yr for G<15, 0.07 mas/yr at G=17, 0.5 mas/yr at G=20, and 1.4 mas/yr at G=21 mag.
•     An overall reduction of systematics has been achieved. E.g., the parallax zero point deduced from the extragalactic sources is about -17 μas. A tentative correction formula for the parallax zero point is provided.

Photometry

•     The G-band photometric uncertainties are ~0.3 mmag for G<13, 1 mmag at G=17, and 6 mmag at G=20 mag.
•     The G_BP-band photometric uncertainties are ~0.9 mmag for G<13, 12 mmag at G=17, and 108 mmag at G=20 mag.
•     The G_RP-band photometric uncertainties are ~0.6 mmag for G<13, 6 mmag at G=17, and 52 mmag at G=20 mag.

Radial velocities

•     Gaia EDR3 does not contain new radial velocities. The radial velocities of Gaia Data Release 2 have been added to Gaia EDR3 in order to ease the combination of spectrosopic and astrometric data.
•     Gaia EDR3 hence contains Gaia DR2 median radial velocities for about 7.21 million stars with a mean G magnitude between ~4 and ~13 and an effective temperature (T_eff) in the range ~3550 to 6900 K. The overall precision of the radial velocities at the bright end is of the order of ~200-300 m s^-1 while at the faint end, the overall precision is ~1.2 km s^-1 for a T_eff of 4750 K and ~3.5 km s^-1 for a T_eff of 6500 K.
•     Before publication in Gaia EDR3, an additional filtering has been performed onto the Gaia DR2 radial velocities to remove some 4,000 sources that had wrong radial velocities.
•     Please be aware that the Gaia DR2 values are assigned to the Gaia EDR3 sources through an internal cross-match operation. In total, ~10,000 Gaia DR2 radial velocities could not be associated to a Gaia EDR3 source.

Astrophysical parameters

• Gaia EDR3 does not contain new astrophysical parameters. Astrophysical parameters have been published in Gaia DR2 and a new set is expected to be released with the full Gaia DR3 release.

Variable stars

•  Gaia EDR3 does not contain newly classified variable stars. For the overview of the currently available variable stars from Gaia DR2, have a look the Gaia Data Release 2 contents page. Classifications for a larger set of variable stars are expected with the full Gaia DR3 release.

Solar system objects

• A large set of solar system objects with orbits will become available with the full Gaia DR3 release. Information on the currently available asteroids in Gaia DR2 can be found on the Gaia Data Release 2 contents page.

Gaia EDR3 passbands, data model and additional information

Information about Gaia EDR3 passbands, data model, and known issues will be available from Gaia EDR3 page on ESA website.

A draft data model documentation is available for download from ESA's Gaia EDR3 page.

For Gaia EDR3 documentation see https://gea.esac.esa.int/archive/documentation/GEDR3/

Gaia EDR3 data

The Gaia Archive is the main point of access for the Gaia Early DR3 data, but the data is also served from Gaia partner data centres (CDS, ASDC, ARI, and AIP). Data can be extracted from the Gaia Archive by performing ADQL queries and subsequently downloading the corresponding results tables.

The Gaia EDR3 data set will also be downloadable in compressed CSV-format with the total size of the downloadable data expected to be in the order of 1.3 TB. The increased size, compared to Gaia DR2, is mostly due to the addition of extra information from the Gaia Object Generator (GOG) and Gaia Universe Model Snapshot (GUMS), and due to the increase in the number of sources in the catalogue. The cross-matches with external catalogues will also be made available for bulk download.

Gaia EDR3 papers

The following papers will accompany Gaia EDR3.

Summary papers

These papers provide an overview of the Gaia mission and the contents of Gaia Early Data Release 3 and summarise specifics of the survey. The Gaia Early Data Release 3 paper also discusses the limitations of the Gaia Early DR3 data and provides recommendations for responsible use.

Description of the Gaia mission (spacecraft, instruments, survey and measurement principles), Gaia Collaboration, Prusti, T., et al. (2016)

Gaia Early Data Release 3: Summary of the contents and survey properties, Gaia Collaboration, Brown, A.G.A., et al.(arXiv) (accompanying source code)

Processing papers

These expected papers will give technical details on the processing and calibration of the raw data and the path taken to arrive at Gaia Early Data Release 3. The processing papers are complementary to the Gaia Data Release Documentation.

Link to the A&A page for Gaia Early Data Release 3.

Gaia Early Data Release 3: The astrometric solution, Lindegren, L., et al. (arXiv)

Gaia Early Data Release 3: Photometric content and validation, Riello, M., et al. (arXiv) (accompanying source code)

Gaia Early Data Release 3: Parallax bias versus magnitude, colour and position, Lindegren, L., et al. (arXiv) (accompanying source code)

Gaia Early Data Release 3: The celestial reference frame (GAIA-CRF3), Gaia Collaboration, et al.

Gaia Early Data Release 3: Updated radial velocities from Gaia DR2, Seabroke, G.M., et al.

Gaia Early Data Release 3: Catalogue Validation, Fabricius, C., et al.

Gaia Early Data Release 3: Building the Gaia DR3 source list - Cross-match of Gaia observations, Torra, F., et al.

Gaia Early Data Release 3: Modelling and calibration of Gaia's point and line spread functions, Rowell, N., et al. (arXiv)

Gaia Early Data Release 3: Cross-match with external catalogues - Algorithm and results, Marrese, P., et al.

Performance verification papers

These papers give an overview of the science potential of Gaia Early Data Release 3. Without going into in-depth analysis, they give a short introduction to selected science topics that can be addressed with this release. The purpose of these papers is to demonstrate the scientific quality of the data through examples. These performance verification papers are not exhaustive or definitive treatments of the topics.

Gaia Early Data Release 3: The Gaia catalogue of nearby stars, Gaia Collaboration, Smart, R.L., et al. (arXiv)

Gaia Early Data Release 3: Structure and properties of the Magellanic Clouds, Gaia Collaboration, Luri, X., et al. (arXiv)

Gaia Early Data Release 3: The Galactic anticentre, Gaia Collaboration, Antoja, T., et al.

Gaia Early Data Release 3: Acceleration of the solar system from Gaia astrometry, Gaia Collaboration, Klioner, S.A., et al. (arXiv)