# Gaia Data Release 3 Documentation release 1.1

European Space Agency (ESA)
and
Gaia Data Processing and Analysis Consortium (DPAC)
13 June 2022
###### Executive summary

The third Gaia data release, Gaia DR3, contains the astrometry and broad-band photometry already published as part of Gaia EDR3 and introduces a large variety of new data products:

• A much expanded radial velocity survey, as well as magnitudes of sources in the $G_{\rm RVS}$ band, and a spectral line broadening parameter $v_{\mathrm{broad}}$;

• Mean BP, RP, and RVS spectra for a large subset of sources;

• A much expanded collection of variable sources, covering 24 variability types;

• Photometric time series for all variable sources;

• The Gaia Andromeda Photometric Survey which contains the photometric time series for all sources (variable and non-variable) in a $5.5^{\circ}$ radius field around M31;

• Object classification, including a self-organised map (SOM) of poorly classified sources;

• Astrophysical parameters (APs) from mean BP/RP spectra, including Markov-Chain Monte Carlo (MCMC) samples;

• Astrophysical parameters from mean RVS spectra;

• Chemical abundances from mean RVS spectra;

• Diffuse interstellar band parameters from mean RVS spectra;

• Non-single star solutions;

• QSO and galaxy candidates, including redshifts, QSO host detections, and QSO host and galaxy light profiles;

• Solar system objects (SSO), including reflectance spectra derived from epoch BP/RP spectra;

• Total galactic extinction maps at various HEALPix levels;

The archive contents are summarized in Table 0.1 and Table 0.2, while Table 0.3 provides a list of all tables available in the Gaia DR3 archive.

The astrometric data in Gaia DR3 are the same as those of Gaia EDR3, hence there is a global parallax bias, in the sense Gaia $-$ ‘true’, of about $-0.017$ mas, which has not been ‘corrected’ in the data. Details are provided by (Lindegren et al. 2020), including a proposed recipe for correcting the parallaxes for the bias as a function of sky position, $G$ magnitude and colour $G_{\mathrm{BP}}-G_{\mathrm{RP}}$. The broad-band photometric contents ($G$, $G_{\rm BP}$, $G_{\rm RP}$) are also the same as in Gaia EDR3 with the following exception. For Gaia EDR3 a milli-magnitude level correction was applied to the $G$-band photometry for sources with 6-parameter and 2-parameter astrometric solutions. This correction was provided in the form of Python code and Astronomical Data Query Language (ADQL) recipes. These corrections are included in Gaia DR3 and should thus not be applied when working with broad-band photometry extracted from the Gaia DR3 data tables in the Gaia archive.

The data collected between 25 July 2014 and 28 May 2017 – during the first 34 months of the Gaia mission – have been processed by the Gaia Data Processing and Analysis Consortium (DPAC), resulting in Gaia DR3. A summary of the release properties is provided in Gaia Collaboration et al. (2022k). The overall scientific validation of the data is described in Babusiaux et al. (2022) and Fabricius et al. (2021) (astrometry, broad-band photometry). Background information on the Gaia  mission and the spacecraft can be found in Gaia Collaboration et al. (2016b), with a more detailed presentation of the Radial Velocity Spectrometer (RVS) in Cropper et al. (2018). In addition, Gaia DR3 is accompanied by dedicated papers, all part of a Special Issue of A&A, that describe the processing and validation of the various data products: Lindegren et al. (2021) for the Gaia DR3 astrometry, Riello et al. (2021) for the Gaia DR3 photometry, and Gaia Collaboration et al. (2022g) for the Gaia celestial reference frame.

The processing of the BP/RP spectra for Gaia DR3 is described in De Angeli et al. (2022), with details on the internal calibration model provided in Carrasco et al. (2021). The external flux calibration is described in Montegriffo et al. (2022) and is based on a set of spectro-photometric calibrators described in Pancino et al. (2021) and references therein. The processing of the RVS spectra and the various data products derived from these spectra is described in Katz et al. (2022) (radial velocity processing and validation), Blomme et al. (2022b) (radial velocities of hot stars), Damerdji et al. (2022) (double-lined spectra), Frémat et al. (2022) (determination of $v_{\mathrm{broad}}$), Sartoretti et al. (2022) ($G_{\rm RVS}$ magnitudes and the RVS pass-band), and Seabroke and et al. (2022) (mean RVS spectra).

The Gaia Andromeda Photometric Survey consists of broad-band photometric time series for all sources (variable and non-variable) located in a $5.5^{\circ}$ radius region centred on M31. This survey is described in Evans et al. (2022) and is based on the photometry presented in Riello et al. (2021).

An overview of the variable source processing and analysis can be found in Eyer et al. (2022). Specific aspects of the variable source processing are described in: Gavras et al. (2022) (cross-match of Gaia DR3 sources with variable sources from the literature); Rimoldini et al. (2022) (machine learning classification of variable sources); Clementini et al. (2022) and Ripepi et al. (2022) (Cepheids and RR Lyrae stars, including radial velocity time series); Lebzelter et al. (2022) (long period variables); Distefano et al. (2022) (solar-like variability and rotational modulation); Marton (2022) (young stellar objects); Wyrzykowski et al. (2022) (microlensing events); Mowlavi et al. (2022) (eclipsing binaries); Gomel et al. (2022) (ellipsoidal variables with possible compact object secondaries); Panahi et al. (2022) (candidate transiting exoplanets); and Carnerero et al. (2022) (active galactic nuclei).

Non-single star solutions are provided for the first time in Gaia DR3, including astrometric (Halbwachs et al. 2022), spectroscopic (Gosset 2022), and eclipsing binaries (Siopis 2022) (where solutions from the combinations of astrometry and radial velocities, or eclipsing binary light curves and radial velocities are also provided). Details on the astrometric determination for systems with sub-stellar companions are provided in Holl et al. (2022b). Relevant to both non-single stars and variable sources, Holl et al. (2022a) discuss how the Gaia scanning law can introduce spurious periods in the analysis of photometric, astrometric, or radial velocity time series.

The extragalactic content of Gaia DR3 is described in Gaia Collaboration et al. (2022b). The process of estimating light profiles of extended objects (resolved galaxies and QSO host galaxies) is detailed in Ducourant et al. (2022), and Delchambre et al. (2022) describe the classification of QSOs and unresolved galaxies and how redshifts are derived for these objects.

The processing and validation of the solar system objects in Gaia DR3 is described in Tanga et al. (2022) (astrometry, photometry, orbits) and in Gaia Collaboration et al. (2022f) (BP/RP reflectance spectra).

Gaia DR3 presents a classification of the majority of sources in the Gaia source list and a large collection of astrophysical data. This data is derived from the combination of basic Gaia observational data, the parallaxes, BP/RP and RVS spectra, and the broad-band photometry. An overview of the processing modules that classify sources and derive astrophysical parameters is provided in Creevey et al. (2022). Fouesneau et al. (2022b) and Delchambre et al. (2022) provide more details on the quality and validation of the stellar and non-stellar parameters, respectively. The latter include total galactic extinction maps and an analysis of outliers in the space of BP/RP spectra in addition to the extragalactic content mentioned above. Details on the extraction of the main astrophysical parameters from the BP/RP spectra is given in Andrae et al. (2022). From the RVS spectra stellar atmospheric parameters and detailed abundances are derived, as well as the parameters of the diffuse interstellar bands present in these spectra. The details are provided by Recio-Blanco and et al. (2022). From the Calcium infrared triplet in the RVS spectra one can also derive a chromospheric activity index. This process is described in Lanzafame et al. (2022).

Nine papers accompanying Gaia DR3 provide an impression on the immense scientific potential of this release. Gaia Collaboration et al. (2022c) presents clean samples of high quality astrophysical parameters of several specific types of stars. Gaia Collaboration et al. (2022i) uses Gaia astrometry, radial velocities and element abundances derived from RVS mean spectra to conduct a chemo-dynamical analysis of Milky Way disc and halo populations. Gaia Collaboration et al. (2022j) discusses the distribution of the diffuse interstellar band at 862 nm in the context of interstellar extinction within a few $\,\rm kpc$ from the Sun. Gaia Collaboration et al. (2022e) explores non-axisymmetric features in the disc of the Milky Way, spiral arms and the bar, in both configuration and velocity space. Gaia Collaboration et al. (2022a) presents a clean catalogue of binary stars, discussing its completeness and some statistical features of the orbital elements in comparison with external catalogues. In addition, a catalogue of tens of thousands of masses of binary components is provided. Gaia Collaboration et al. (2022f) presents reflectance spectra, derived from BP/RP spectra, for solar system objects, discussing the scientific potential of the combination of accurate orbital data and composition information derived from the reflectance spectra. Gaia Collaboration et al. (2022h) shows how synthetic photometry can be obtained from flux calibrated BP/RP spectra for any pass-bands fully enclosed in the Gaia wavelength range. Applications employing synthetic photometry for a number of well known photometric systems are discussed. Gaia Collaboration et al. (2022d) investigates the properties of high-mass main sequence pulsators, showing that Gaia DR3 data are suitable for the identification of nearby OBAF-type pulsators. Finally, Gaia Collaboration et al. (2022b) summarises the Gaia processing of extragalactic sources, describing the statistical properties of two high purity samples of galaxies and QSOs available in Gaia DR3. For several of the above papers there are accompanying data that are also included in Gaia DR3: a subset of the samples defined in Gaia Collaboration et al. (2022c) (archive tables gaiadr3.gold_sample_*), the synthetic photometry from Gaia Collaboration et al. (2022h) (archive table gaiadr3.synthetic_photometry_gspc), binary component masses from Gaia Collaboration et al. (2022a) (archive table gaiadr3.binary_masses), as well as solar system object osculating orbital elements from Tanga et al. (2022) (archive table gaiadr3.sso_orbits).

Data from Gaia DR3, as well as from Gaia DR1, Gaia DR2, and Gaia EDR3, can be retrieved from the Gaia ESA Archive (GEA), which is accessible from https://archives.esac.esa.int/gaia. The archive also provides various tutorials on data access and data queries plus an integrated data model (i.e., description of the various fields in the data tables). In addition, Luri et al. (2018) provide concrete advice on how to deal with Gaia astrometry, with recommendations on how best to estimate distances from parallaxes. The Gaia archive features a visualisation service which can be used for quick initial explorations of the entire Gaia DR3 data set. Carefully validated, pre-computed cross matches between Gaia DR3 and a selected set of large surveys is provided, with details described in Marrese et al. (2019, 2022). Finally, Gaia DR3 contains the (intended) pointing of the Gaia telescopes as a function of time (commanded_scan_law table) and simulated Gaia catalogues (gaia_universe_model and gaia_source_simulation tables).

Gaia DR3 includes large amounts of data which are not easily stored in standard tabular form. This concerns the mean BP/RP/RVS spectra, photometric time series, and Markov-Chain Monte Carlo samples. Instead, these products are hosted by a dedicated service designed to handle massive data requests that is accessible via the DataLink protocol. How to discover and access the DataLink products in Gaia DR3 is described here.

Through the Gaia DR3 web pages several supplementary sets of information will be provided:

• Any issues with the Gaia DR3 contents arising after the publication of the release will be listed on the “known issues” pages.