Gaia Early Data Release 3 (Gaia EDR3)

 

Gaia Data Release 3 is split into two releases: the early release called Gaia Early Data Release 3 (Gaia EDR3) and the full Gaia Data Release 3 (Gaia DR3). Gaia EDR3 is planned to be released on 3 December 2020 at 12:00 CET. The full Gaia Data Release 3 (Gaia DR3) is planned for the first half of 2022.

As for previous releases, the Gaia (E)DR3 data will be made available through the Gaia Archive and partner data centres. A description of the expected contents of Gaia Early DR3 is given below. An overview page for Gaia Early Data Release 3 helps to find all relevant information for the Gaia EDR3 release. All numbers are based on estimates done after processing and are subject to successful validation. More detailed information on the expected contents for the full Gaia DR3 release will follow later.

 

Contents of Gaia EDR3

 

  • The five-parameter astrometric solution - positions on the sky (α, δ), parallaxes, and proper motions - for around 1.5 billion (1.5 109) 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.
  • In addition, two-parameters solutions - positions on the sky (α, δ) - for around 300 million additional sources.
  • G magnitudes for around 1.8 billion sources.
  • GBP and GRP magnitudes for around 1.5 billion sources.
  • Please be aware that the photometric system for the G, GBP, and GRP bands in Gaia EDR3 is different from the photometric system as used in Gaia DR2 and Gaia DR1.
  • Full passband definitions for G, GBP, and GRP. More information will become available here.
  • About 1.5 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 EDR3 to Gaia DR2 match will be provided.
  • 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 Gaia DR2 radial velocities.

The below table gives an overview of Gaia Early Data Release 3 in numbers:

 

  # sources in Gaia EDR3 # sources in Gaia DR2 # sources in Gaia DR1
Total number of sources ≈ 1,800,000,000 1,692,919,135 1,142,679,769
Number of 5-parameter sources ≈ 1,500,000,000 1,331,909,727 2,057,050
Number of 2-parameter sources ≈ 300,000,000 361,009,408 1,140,622,719
Sources with mean G magnitude ≈ 1,800,000,000 1,692,919,135 1,142,679,769
Sources with mean GBP-band photometry ≈ 1,500,000,000 1,381,964,755 -
Sources with mean GRP-band photometry ≈ 1,500,000,000 1,383,551,713 -
Gaia-CRF sources ≈ 1,500,000 556,869 2,191
Sources with radial velocities expected with Gaia DR3 / ≈7,210,000 from Gaia DR2 in Gaia EDR3 7,224,631 -
Variable sources expected with Gaia DR3 / see Gaia DR2 550,737 3,194
Known asteroids with epoch data expected with Gaia DR3 / see Gaia DR2 14,099 -
Effective temperatures (Teff) expected with Gaia DR3 / see Gaia DR2 161,497,595 -
Extinction (AG) and reddening (E(GBP-GRP)) expected with Gaia DR3 / see Gaia DR2 87,733,672 -
Sources with radius and luminosity expected with Gaia DR3 / see Gaia DR2 76,956,778 -
and more... expected with Gaia DR3 - -

 

This table provides an overview of the expected sources in Gaia Early Data Release 3 (Gaia EDR3). For user convenience, Gaia Data Release 2 radial velocities are provided for Gaia EDR3 sources along with the Gaia EDR3 data. Gaia EDR3 will not contain other data: no variables, no solar system objects, and no astrophysical parameters. These data products, including "new" radial velocities, will be provided in Gaia DR3.

 

 

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 will be 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 parallax improvement is typically 20% with respect to Gaia DR2.
  • The proper motions are typically a factor two better than in Gaia DR2.
  • An overall reduction of systematics has been achieved. E.g., the parallax zero point deduced from the extragalactic sources is about -20 μas. A tentative correction formula for the parallax zero point will be provided.
  • Closer to the release date of Gaia Early Data Release 3, an update will be given on the astrometry.

Photometry

  • The G-band photometric uncertainties are ~0.25 mmag for G<13, 1 mmag at G=17, and 5 mmag at G=20 mag.
  • The GBP-band photometric uncertainties are ~1 mmag for G<13, 10 mmag at G=17, and 100 mmag at G=20 mag.
  • The GRP-band photometric uncertainties are ~1 mmag for G<13, 5 mmag at G=17, and 50 mmag at G=20 mag.
  • Closer to the release date of Gaia Early Data Release 3, an update will be given on the photometry.

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 (Teff) 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 Teff of 4750 K and ~3.5 km s-1 for a Teff 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 here. 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 here.

 

Passbands

 

Gaia EDR3 passbands will be released for use in scientific exploitation.

 

Documentation

 

Data release documentation is provided along with each data release in the form of a downloadable PDF and a webpage. The various chapters of the documentation have been indexed at ADS allowing them to be cited. Please visit the Gaia Archive to access this documentation, and make sure to check out all relevant information given through the documentation overview page.

 

Known issues with Gaia Early Data Release 3

 

Similarly as is done for Gaia Data Release 2, we will inform you of any issues with the data or with the information that is given along with the data that is discovered after the official release. A link to this information will be provided here.

 

Data model

 

The Gaia EDR3 data model describes all tables together with the names and contents of the columns inside each table. This information will become available from the Gaia Archive along with the release of the data. A draft version of the data model can be found below for download. The draft version is provided to help you get prepared for the release. Please bear in mind that this is a draft chapter of the main Gaia EDR3 data release documentation, and references to other parts of the data release documentation may be missing. A full release of the Gaia EDR3 data model will be made public with the release of the Gaia EDR3 data.

Download the Gaia EDR3 draft data model here

 

Data Release papers

 

Along with the data release documentation, several data processing papers will be published describing the specifics of the data processing and validation performed by the different coordination units in the Gaia Data Processing and Analysis Consortium (DPAC). There will also be some papers on the performance verification of Gaia EDR3, providing basic demonstrations of the scientific potential of the Gaia EDR3 catalogue.

The titles of these papers will be announced in due time.

 

Accessing the DATA

 

The Gaia Archive is the main point of access for the Gaia Early DR3 data, but the data is also served from our 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.