[Paper Review] Gaia Early Data Release 3

M. Riello, F. De Angeli+40 more|arXiv (Cornell University)|Dec 3, 2020

Stellar, planetary, and galactic studies50 references20 citations

TL;DR

This paper presents Gaia Early Data Release 3 (EDR3), detailing significant improvements in photometric processing over DR2, including enhanced background estimation, refined calibration models accounting for flux loss, and better handling of saturation and crowding. The result is sub-millimagnitude precision (0.2 mmag at G = 10–14) with no major systematic trends above 1 mmag/mag, marking a major advance in photometric accuracy and homogeneity for 1.8 billion sources.

ABSTRACT

Context. Gaia Early Data Release 3 ( Gaia EDR3) contains astrometry and photometry results for about 1.8 billion sources based on observations collected by the European Space Agency Gaia satellite during the first 34 months of its operational phase. Aims. In this paper, we focus on the photometric content, describing the input data, the algorithms, the processing, and the validation of the results. Particular attention is given to the quality of the data and to a number of features that users may need to take into account to make the best use of the Gaia EDR3 catalogue. Methods. The processing broadly followed the same procedure as for Gaia DR2, but with significant improvements in several aspects of the blue and red photometer (BP and RP) preprocessing and in the photometric calibration process. In particular, the treatment of the BP and RP background has been updated to include a better estimation of the local background, and the detection of crowding effects has been used to exclude affected data from the calibrations. The photometric calibration models have also been updated to account for flux loss over the whole magnitude range. Significant improvements in the modelling and calibration of the Gaia point and line spread functions have also helped to reduce a number of instrumental effects that were still present in DR2. Results. Gaia EDR3 contains 1.806 billion sources with G -band photometry and 1.540 billion sources with G BP and G RP photometry. The median uncertainty in the G -band photometry, as measured from the standard deviation of the internally calibrated mean photometry for a given source, is 0.2 mmag at magnitude G = 10–14, 0.8 mmag at G ≈ 17, and 2.6 mmag at G ≈ 19. The significant magnitude term found in the Gaia DR2 photometry is no longer visible, and overall there are no trends larger than 1 mmag mag −1 . Using one passband over the whole colour and magnitude range leaves no systematics above the 1% level in magnitude in any of the bands, and a larger systematic is present for a very small sample of bright and blue sources. A detailed description of the residual systematic effects is provided. Overall the quality of the calibrated mean photometry in Gaia EDR3 is superior with respect to DR2 for all bands.

Motivation & Objective

• To improve the photometric calibration and data quality of Gaia's early data releases.
• To address residual systematics and instrumental effects present in Gaia DR2, particularly in the BP and RP bands.
• To deliver a more homogeneous, precise, and accurate photometric catalogue for astronomical research.
• To validate the performance of the new processing pipeline across the full magnitude and colour range.
• To provide users with guidelines and known issues to ensure optimal use of the EDR3 photometric data.

Proposed method

• Reprocessing of 34 months of Gaia observations (July 2014–May 2017) using enhanced calibration models.
• Improved background estimation in BP, RP, and G bands, eliminating zodiacal light residuals seen in DR2.
• Incorporation of flux loss corrections across the full magnitude range in photometric calibration.
• Enhanced treatment of saturation and crowding effects, reducing spurious features like the G = 11.2 bump.
• Use of a single passband across all magnitudes and colours to minimize systematics.
• Exclusion of low-quality data periods and pre-filtering of problematic observations to improve overall calibration stability.

Experimental results

Research questions

• RQ1 How has the photometric calibration in Gaia EDR3 improved over DR2 in terms of systematic errors and precision?
• RQ2 What impact do enhanced background estimation and flux loss corrections have on photometric accuracy?
• RQ3 Are there residual systematics in the G, GBP, and GRP bands, particularly for bright or blue sources?
• RQ4 How does the inclusion of an additional year of data affect the uncertainty and stability of mean photometry?
• RQ5 To what extent do instrumental effects such as saturation and crowding influence the final photometric results?

Key findings

• The median uncertainty in G-band photometry is 0.2 mmag at G = 10–14, 0.8 mmag at G ≈17, and 2.6 mmag at G ≈19, representing a significant improvement over DR2.
• The magnitude-dependent systematic trend present in Gaia DR2 is no longer visible, with no trends exceeding 1 mmag/mag across the magnitude range.
• Using a single passband across all magnitudes and colours results in systematics below 1% in magnitude for all bands, increasing only to ~2% for 4,148 bright, blue sources (G < 13, GBP−GRP < −0.1).
• Improved background estimation eliminates zodiacal light residuals, which were visible in Gaia DR2, particularly in the GBP and GRP bands.
• Saturation handling has been significantly improved, reducing the characteristic bump at G = 11.2 and minimizing corrections for G < 6.
• The consistency between G, GBP, and GRP photometry has improved, and discontinuities at G = 13 and 16—present in DR1 and DR2—have been eliminated.