Selection functions of large spectroscopic surveys

TL;DR

This paper introduces a new method to estimate the selection function of large spectroscopic surveys, improving the accuracy of Galactic stellar population studies by accounting for survey biases.

Contribution

The authors develop a median division binning algorithm for estimating survey selection functions, validated through simulations and applied to multiple public surveys.

Findings

The method reduces biases compared to traditional 2D-histograms.

Selection functions significantly affect distance and metallicity distributions in inhomogeneous surveys.

The code for estimating selection functions is publicly available.

Abstract

Context. Large spectroscopic surveys open the way to explore our Galaxy. In order to use the data from these surveys to understand the Galactic stellar population, we need to be sure that stars contained in a survey are a representative subset of the underlying population. Without the selection function taken into account, the results might reflect the properties of the selection function rather than those of the underlying stellar population. Aims. In this work, we introduce a method to estimate the selection function for a given spectroscopic survey. We apply this method to a large sample of public spectroscopic surveys. Methods. We apply a median division binning algorithm to bin observed stars in the colour-magnitude space. This approach produces lower uncertainties and lower biases of the selection function estimate as compared to traditionally used 2D-histograms. We run a set of simulations to verify the method and calibrate the one free parameter it contains. These simulations allow us to test the precision and accuracy of the method. Results. We produce and publish estimated values and uncertainties of selection functions for a large sample of public spectroscopic surveys. We publicly release the code used to produce the selection function estimates. Conclusions. The effect of the selection function on distance modulus and metallicity distributions of stars in surveys is important for surveys with small and largely inhomogeneous spatial coverage. For surveys with contiguous spatial coverage the effect of the selection function is almost negligible.