End-to-end ground calibration and in-flight performance of the FIREBall-2 instrument

The payload of the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2), the second generation15 of the FIREBall instrument (PI: C. Martin, Caltech), has been calibrated and launched from the NASA Columbia Sci16entific Balloon Facility (CSBF) in Fort Sumner, NM. FIREBall-2 was launched for the first time on the 22nd September17 2018, and the payload performed the very first multi-object acquisition from space using a multi-object slit spectro18graph (MOS). This performance-oriented paper presents the calibration and last ground adjustments of FIREBall-2,19 the in-flight performance assessed based on the flight data, and the predicted instrument’s ultimate sensitivity. This20 analysis predicts that future flights of FIREBall-2 should be able to detect the HI Ly↵ resonance line in galaxies at21 z ⇠ 0.67, but will find it challenging to spatially resolve the circumgalactic medium (CGM).