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gaia data release 3 documentation

14.3 Comparison to models

14.3.7 Astrophysical parameters from GSP-Phot and GSP-Spec

Statistics of astrophysical parameters obtained from GSP-Phot and GSP-Spec are computed in each HEALPix pixel, and in G bin of 1 mag. The resulting maps are shown in Figure 14.50 for GSP-Phot and Figure 14.51 for GSP-Spec, in the G=12 to 13 magnitude range, for Gaia DR3 (left panels), GOG20 (middle panels), and their difference DR3-GOG20 (right panels).

Figure 14.50: From top to bottom: median of Teff, AG, [M/H], logg computed in HEALPix pixels, in Gaia DR3 (GSP-Phot, left), in GOG20 (middle) and their differences (right), in the magnitude range 12<G<13.
Figure 14.51: From top to bottom: median of Teff, [M/H], [α/Fe], logg computed in HEALPix pixels, in Gaia DR3 (GSP-Spec, left), in GOG20 (middle) and their differences (right), in the magnitude range 12<G<13.

The comparison is satisfactory, accounting for uncertainties on the extinction model in GOG20. However the [M/H] and [α/Fe] distributions seem to follow extinction features, which is not predicted by the model. This may be due to a correlation of the determination of these parameters with AG.

The median values over the whole sky are shown as a function of G in Figure 14.52 for Gaia DR3 (GSP-Phot in blue, GSP-Spec in pink), and GOG20 (green). At G>12 the GSP-Spec values deviate from that predicted, most probably due to the lack of values measured at these magnitudes. On the bright side (G<10), the disagreement is still large for GSP-Phot (excepted for [M/H]). It is a bit surprising that bright stars have under-solar metallicities in the mean.

Figure 14.52: Median of astrophysical parameters over the whole sky as a function G magnitude, for Gaia DR3 (GSP-Phot, blue, GSP-Spec, pink) and GOG20 (green).

We also performed direct comparisons of astrophysical parameters from queries in data and simulated catalogues, in different Galactic directions. The results are summarised below.

Summary of the results:

  • The overall agreement between data and model is good but differences can be large in the Galactic plane, linked to the extinction.

  • The [M/H] and [α/Fe] determinations seem to suffer from correlation with the extinction .

  • The high number of large AG values, including at high galactic latitudes, is questionable.

  • The [M/H] shows a low-metallicity tail not expected from the simulation.

  • The [α/Fe] distribution is narrower than the simulated one, with no value smaller than -0.1 dex or greater than 0.4 dex.