A complex multi-notch astronomical filter to suppress the bright infrared sky

TL;DR

This paper introduces a novel multi-notch astronomical filter designed to suppress bright hydroxyl emission lines in the near-infrared sky, enabling deeper observations of the early Universe with current and future telescopes.

Contribution

The paper presents the first on-sky demonstration of a complex multi-notch filter that selectively removes atmospheric emission lines while maintaining high throughput.

Findings

Successful on-sky testing of the filter

Enhanced capability for deep near-infrared observations

Potential to improve early Universe studies

Abstract

A long-standing and profound problem in astronomy is the difficulty in obtaining deep near-infrared observations due to the extreme brightness and variability of the night sky at these wavelengths. A solution to this problem is crucial if we are to obtain the deepest possible observations of the early Universe since redshifted starlight from distant galaxies appears at these wavelengths. The atmospheric emission between 1000 nm and 1800 nm arises almost entirely from a forest of extremely bright, very narrow hydroxyl emission lines that varies on timescales of minutes. The astronomical community has long envisaged the prospect of selectively removing these lines, while retaining high throughput between the lines. Here we demonstrate such a filter for the first time, presenting results from the first on-sky tests. Its use on current 8m telescopes and future 30m telescopes will open up many new research avenues in the years to come.