Accurate measurement of telescope filter bandpasses with a Collimated Beam Projector and impact on cosmological parameters

TL;DR

This paper demonstrates a method using a Collimated Beam Projector to precisely measure telescope filter bandpasses, reducing calibration uncertainties and improving the accuracy of cosmological parameter estimation from photometric surveys.

Contribution

It introduces a novel approach to accurately measure filter bandpasses at the required precision, addressing calibration biases in cosmological measurements.

Findings

Measurement of filter bandpasses at sub-millimeter accuracy.

Quantification of biases caused by bandpass uncertainties.

Potential to improve cosmological parameter constraints.

Abstract

The measurement of magnitudes with different filters in photometric surveys gives access to cosmological distances and parameters. However, for current and future large surveys like the ZTF, DES, HSC or LSST, the photometric calibration uncertainties are almost comparable to statistical uncertainties in the error budget of type Ia cosmology analysis, which limits our ability to use type Ia supernovae for precision cosmology. The knowledge of the bandpasses of the survey filters at the per-mill level can help reach the sub-percent precision for magnitudes. We show how a misknowledge of the bandpasses central wavelengths or of the presence of out-of-band leakages leads to biased cosmological measurements. Then, we present how to measure the filter throughputs at the required precision with a Collimated Beam Projector.