The original optical spectrum published in 1990 (top) compared to the new spectrum taken with the Gemini MultiObject Spectrograph (GMOS).Vertical lines indicate emis sion lines associated with background quasar PKS 0405−385 (red, solid), absorption lines associated with the intervening galaxy detected in FLASH data (blue, dot-dashed), and two further, previously unidentified intervening galaxies (orange, dashed and violet, dotted). From Kerrison et al. 2026

As described in yesterday’s ADAP, Kerrison et al. report the discovery of an intervening neutral hydrogen (HI) 21 cm absorption line at a redshift of z = 0.88 towards the z = 1.284 quasar PKS 0405−385, identified in ASKAP FLASH (First Large Absorption Survey in HI) observations. A low-resolution optical spectrum from the 1990s contained a hint of an absorption system, so a new optical spectrum was obtained to try and confirm this with the 8.1 m Gemini South telescope, using the Gemini MultiObject Spectrograph (GMOS). The figure above shows the original optical spectrum published in 1990 (top) compared to the new GMOS spectrum (bottom). Vertical lines indicate emission lines associated with background quasar PKS 0405−385 (red, solid), absorption lines associated with the intervening galaxy detected in FLASH data (blue, dot-dashed), and two further, previously unidentified intervening galaxies (orange, dashed and violet, dotted). With the benefit of hindsight, a number of lines from both intervening systems are visible (at low significance) in the original spectrum. A re-examination of the FLASH spectrum reveals no H I detection of the new z = 0.907 and z = 0.966 systems.