Completeness of the Gaia-verse

"Which stars did Gaia see and where are they on the sky?"

The Gaia Mission

The Gaia space telescope was launched by the European Space Agency in 2013 with the goal of mapping the motions and properties of stars in our Galaxy, as well as their planetary companions, asteroids in the Solar system and Quasars in the distant Universe. The ground-breaking second data release in April 2018 contained close to two billion objects, most of which are stars in our Milky Way. The astrophysical community has used the second data release to find evidence of ancient mergers with dwarf galaxies, warps in the stellar disk and the fastest stars known. However, to turn these features into a true map of our Galaxy will require us to understand the completeness of the Gaia catalogue: which stars did Gaia see and where are they on the sky?

Our mission

Knowing the completeness of a catalogue is vital if you want to extrapolate from statements about the objects in that catalogue to constrain the physical properties of our Universe. Our goal is to infer the completeness of the Gaia catalogue in a principled way that accounts for the unique way that Gaia scans the sky. Our task is made more complex by the multi-faceted nature of the data products: astrometry, photometry and spectroscopy - in addition to the derived astrophysical parameters, binary star solutions and variable classifications - and each member of this Gaia-verse of catalogues is differently complete. We plan to develop an open-source Python package to make accounting for the completeness the easy first step of any analysis.

Examples of questions we want to answer with this project:

  1. What are the odds that this faint star is in Gaia DR2?

  2. What are the odds that this faint star has a proper motion in Gaia DR2?

  3. What are the odds that this faint star has a proper motion in Gaia DR2 and a radial velocity in APOGEE DR14?