Gaia Early Data Release 3 (Gaia EDR3)

 

Gaia Data Release 3 is split into two installments: the early release called Gaia Early Data Release 3 (Gaia EDR3) and the full Gaia Data Release 3 (Gaia DR3). Gaia EDR3 is 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 is made available through the Gaia Archive and partner data centres. A description of the 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. More detailed information on the expected contents for the full Gaia DR3 release will follow later.

 

Contents of Gaia EDR3

 

  • The full astrometric solution (5 parameters) - positions on the sky (α, δ), parallaxes, and proper motions - for around 1.468 billion (1.468 109) 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.
  • GBP and GRP magnitudes for around 1.542 billion and 1.555 billion sources, respectively.
  • 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 is available here.
  • About 1.614 million celestial reference frame (Gaia-CRF3) 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 DR2, 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).
  • The commanded scan law covering the Gaia EDR3 data collection period. 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 source table in the Gaia Archive is complemented with a set of (cleaned) 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 1,811,709,771 1,692,919,135 1,142,679,769
Number of 5-parameter sources 585,416,709 1,331,909,727 2,057,050
Number of 6-parameter sources 882,328,109
Number of 2-parameter sources 343,964,953 361,009,408 1,140,622,719
Sources with mean G magnitude 1,806,254,432 1,692,919,135 1,142,679,769
Sources with mean GBP-band photometry 1,542,033,472 1,381,964,755 -
Sources with mean GRP-band photometry 1,554,997,939 1,383,551,713 -
Gaia-CRF sources 1,614,173 556,869 2,191
Sources with radial velocities 7,209,831 (Gaia DR2) 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 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 does 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 Gaia EDR3 are all constructed as follows:

Gaia EDR3 yyy....yy

 

A table to trace sources from Gaia DR2 to Gaia EDR3 is provided since 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 GBP-band photometric uncertainties are ~0.9 mmag for G<13, 12 mmag at G=17, and 108 mmag at G=20 mag.
  • The GRP-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 (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 describe the photometric system for Gaia Early Data Release 3, they can be found here. Both Gaia DR1 and Gaia DR2 comes with their own set of passbands.

 

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

 

If we find any issues with the data or with the information that is given along with the data after the official release, we publish these here.

 

Data model

 

The Gaia EDR3 data model describes all tables of the catalogue together with the names and contents of the columns inside each table.

Update: Of the cross matches mentioned, the following cross matches will be made available later than 3 December 2020: GSC 2.3, APASS dr9, RAVE dr5, TMASS PSC XSC, and allWISE.

 

Data Release papers

 

Along with the data release documentation, several data processing papers have been 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). Next to the processing papers, there are 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 and links to the published papers are here.

 

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) and ESASky. Data can be extracted from the Gaia Archive by performing ADQL queries and subsequently downloading the corresponding results tables.

The Gaia EDR3 data set is also downloadable in compressed CSV format (~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.

The bulk download can be found from the homepage of the Gaia Archive.