Gaia Data Release 3: Properties of the line-broadening parameter derived with the Radial Velocity Spectrometer (RVS)

Context. The third release of the Gaia catalogue contains radial velocities for 33 812 183 stars with effective temperatures ranging from 3100 K to 14 500 K. The measurements are based on the comparison of the spectra observed with the Radial Velocity Spectrometer (RVS; wavelength coverage: 846'870 nm, median resolving power: 11 500) to synthetic data broadened to the adequate along-scan line spread function. The additional line-broadening, fitted as it would only be due to axial rotation, is also produced by the pipeline and is available in the catalogue (field name vbroad). Aims. We describe the properties of the line-broadening information extracted from the RVS and published in the catalogue, and analyse the limitations imposed by the adopted method, wavelength range, and instrument. Methods. We used simulations to express the link between the line-broadening measurement provided in Gaia Data Release 3 and V sin i. We then compared the observed values to the measurements published by various catalogues and surveys (GALAH, APOGEE, LAMOST, etc.). Results. While we recommend caution in the interpretation of the vbroad measurement, we also find a reasonable general agreement of the Gaia Data Release 3 line-broadening values and values in other catalogues. We discuss and establish the validity domain of the published vbroad values. The estimate tends to be overestimated at the lower V sin i end, and at Teff'>'7500'K its quality and significance degrade rapidly when GRVS'>'10. Despite all the known and reported limitations, the Gaia Data Release 3 line-broadening catalogue contains measurements obtained for 3 524 677 stars with Teff ranging from 3500 to 14 500 K, and GRVS'<'12. It gathers the largest stellar sample ever considered for the purpose, and allows a first mapping of the Gaia line-broadening parameter across the Hertzsprung-Russel diagram.