Gaia Data Release 3: The Galaxy in your preferred colours. Synthetic photometry from Gaia low-resolution spectra

TL;DR

Gaia DR3 offers flux-calibrated low-resolution spectra for 220 million sources, enabling accurate synthetic photometry across various passbands, supporting diverse astrophysical research including stellar populations, metallicity, and white dwarf classification.

Contribution

This work introduces a method to derive synthetic photometry from Gaia XP spectra, providing standardized photometry for a vast number of sources and applications in stellar and galactic studies.

Findings

Synthetic photometry matches existing data within a few percent.

Achieves up to millimag accuracy with proper standardization.

Provides catalogs for 220 million sources and 100,000 white dwarfs.

Abstract

Gaia Data Release 3 provides novel flux-calibrated low-resolution spectrophotometry for about 220 million sources in the wavelength range 330nm - 1050nm (XP spectra). Synthetic photometry directly tied to a flux in physical units can be obtained from these spectra for any passband fully enclosed in this wavelength range. We describe how synthetic photometry can be obtained from XP spectra, illustrating the performance that can be achieved under a range of different conditions - for example passband width and wavelength range - as well as the limits and the problems affecting it. Existing top-quality photometry can be reproduced within a few per cent over a wide range of magnitudes and colour, for wide and medium bands, and with up to millimag accuracy when synthetic photometry is standardised with respect to these external sources. Some examples of potential scientific application are presented, including the detection of multiple populations in globular clusters, the estimation of metallicity extended to the very metal-poor regime, and the classification of white dwarfs. A catalogue providing standardised photometry for ~220 million sources in several wide bands of widely used photometric systems is provided (Gaia Synthetic Photometry Catalogue; GSPC) as well as a catalogue of $\simeq 10^5$ white dwarfs with DA/non-DA classification obtained with a Random Forest algorithm (Gaia Synthetic Photometry Catalogue for White Dwarfs; GSPC-WD).