An empirical model of the Gaia DR3 selection function

arXiv (Cornell University)

Abstract

Interpreting and modelling astronomical catalogues requires an understanding of the catalogues' completeness or selection function: objects of what properties had a chance to end up in the catalogue. Here we set out to empirically quantify the completeness of the overall Gaia DR3 catalogue. This task is not straightforward because Gaia is the all-sky optical survey with the highest angular resolution to date and no consistent ``ground truth'' exists to allow direct comparisons. However, well-characterised deeper imaging enables an empirical assessment of Gaia's $G$-band completeness across parts of the sky. On this basis, we devised a simple analytical completeness model of Gaia as a function of the observed $G$ magnitude and position over the sky, which accounts for both the effects of crowding and the complex Gaia scanning law. Our model only depends on a single quantity: the median magnitude $M_{10}$ in a patch of the sky of catalogued sources with $\texttt{astrometric_matched_transits}$ $\leq 10$. $M_{10}$ reflects elementary completeness decisions in the Gaia pipeline and is computable from the Gaia DR3 catalogue itself and therefore applicable across the whole sky. We calibrate our model using the Dark Energy Camera Plane Survey (DECaPS) and test its predictions against Hubble Space Telescope observations of globular clusters. We find that our model predicts Gaia's completeness values to a few per cent across the sky. We make the model available as a part of the $\texttt{gaiasf}$ Python package built and maintained by the GaiaUnlimited project: $\texttt{https://github.com/gaia-unlimited/gaiaunlimited}$

Authors 13

1. T. Cantat-Gaudin

   Max Planck Institute for Astronomy

   Affiliation as printed

   Max-Planck-Institut für Astronomie , Königstuhl 17 , D-69117 Heidelberg , Germany

2. M. Fouesneau

   Max Planck Institute for Astronomy

   Affiliation as printed

   Max-Planck-Institut für Astronomie , Königstuhl 17 , D-69117 Heidelberg , Germany

3. Hans‐Walter Rix

   Max Planck Institute for Astronomy

   Affiliation as printed

   Max-Planck-Institut für Astronomie , Königstuhl 17 , D-69117 Heidelberg , Germany

4. A. Castro-Ginard Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , Niels Bohrweg 2 , 2333 CA Leiden , The Netherlands

5. R. Drimmel

   Osservatorio Astrofisico di Torino · National Institute for Astrophysics

   Affiliation as printed

   INAF -Osservatorio Astrofisico di Torino , Strada Osservatorio 20 , Pino Torinese 10025 Torino , Italy

6. David W. Hogg
7. Andrew R. Casey

   ASTRO-3D · Monash University

   Affiliation as printed

   Centre of Excellence for Astrophysics in Three Dimensions (ASTRO-3D) , Melbourne , Victoria , Australia

   School of Physics & Astronomy , Monash University , Clayton 3800 , Victoria , Australia

8. S. Khanna

   Osservatorio Astrofisico di Torino · National Institute for Astrophysics

   Affiliation as printed

   INAF -Osservatorio Astrofisico di Torino , Strada Osservatorio 20 , Pino Torinese 10025 Torino , Italy

9. Semyeong Oh

   University of Cambridge

   Affiliation as printed

   Institute of Astronomy , University of Cambridge , Madingley Road , Cambridge CB3 0HA , United Kingdom

10. Adrian M. Price Whelan
11. Vasily A Belokurov

    University of Cambridge

    Affiliation as printed

    Institute of Astronomy , University of Cambridge , Madingley Road , Cambridge CB3 0HA , United Kingdom

12. Andrew K. Saydjari

    Harvard University · Center for Astrophysics Harvard & Smithsonian

    Affiliation as printed

    Department of Physics , Harvard University , 17 Oxford St. , Cambridge , MA 02138 , USA

    Harvard-Smithsonian Center for Astrophysics , 60 Garden St. , Cambridge , MA 02138 , USA

13. Gregory Green

    Max Planck Institute for Astronomy

    Affiliation as printed

    Max-Planck-Institut für Astronomie , Königstuhl 17 , D-69117 Heidelberg , Germany