FIREBall-2: The Faint Intergalactic Medium Redshifted Emission Balloon Telescope

TL;DR

FIREBall-2 is a balloon-borne telescope designed to observe faint emission from the circumgalactic medium at redshift ~0.7, with recent redesigns and successful system tests despite an early flight termination.

Contribution

This paper reports on the design, modifications, and testing of the FIREBall-2 telescope and spectrograph for observing the circumgalactic medium at moderate redshift.

Findings

Successful flight testing of new pointing control system

Validation of UV-optimized EMCCD and aspheric grating

Identification of increased noise due to stray light

Abstract

The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall) is a mission designed to observe faint emission from the circumgalactic medium of moderate redshift (z~0.7) galaxies for the first time. FIREBall observes a component of galaxies that plays a key role in how galaxies form and evolve, likely contains a significant amount of baryons, and has only recently been observed at higher redshifts in the visible. Here we report on the 2018 flight of the FIREBall-2 Balloon telescope, which occurred on September 22nd, 2018 from Fort Sumner, New Mexico. The flight was the culmination of a complete redesign of the spectrograph from the original FIREBall fiber-fed IFU to a wide-field multi-object spectrograph. The flight was terminated early due to a hole in the balloon, and our original science objectives were not achieved. The overall sensitivity of the instrument and telescope was 90,000 LU, due primarily to increased noise from stray light. We discuss the design of the FIREBall-2 spectrograph, modifications from the original FIREBall payload, and provide an overview of the performance of all systems. We were able to successfully flight test a new pointing control system, a UV-optimized, delta-doped and coated EMCCD, and an aspheric grating. The FIREBall-2 team is rebuilding the payload for another flight attempt in the Fall of 2021, delayed from 2020 due to COVID-19.