Who is In, and Who is Not? Determining the Gaia Survey Selection Function

The European Space Agency's Gaia mission is the most successful European space mission as measured by the rate of publications appearing that use Gaia's data.

The astrometric, photometric, and radial velocity catalogues provided through the second Gaia data release in April 2018 are the standard in fundamental astronomical data, with much more and much richer data appearing in future Gaia data releases.

However the full transformative potential of the Gaia mission is currently not being realized because we lack a detailed description of the survey selection function: the probability that an astronomical object of certain properties enters the Gaia catalogue (or not).

We illustrate that without the selection function it is impossible to obtain insights in fundamental physics and astrophysics from modeling the objects' population properties, based on a set of catalogue entries.

It is the objective of this proposal to research, develop, and implement the Gaia survey selection function, as well selection functions for Gaia combined with other surveys.

We will make available publicly the data products and open source computer applications needed by scientists to apply the selection functions to their analyses of the Gaia data.

A well-characterized selection function is indispensable to tap the full transformational information content of this flagship European space mission, opening up qualitatively new ways of science analysis, offering more publications, and better reproducibility of the results.

The Gaia survey data will set the standard in fundamental astronomical data for decades to come and the efforts proposed here will contribute to a much increased legacy value of this space mission.