GLASS-z12, also named GHZ2 (formerly known as GLASS-z13) is a Lyman-break galaxy discovered by the Grism Lens-Amplified Survey from Space (GLASS) observing program using the James Webb Space Telescope's NIRCam in July 2022.[8][9]
It has a spectroscopic redshift of 12.34, making it one of the most distant galaxies and astronomical objects ever discovered. According to current theory, this redshift corresponds to a time about 13.44 billion years ago, approximately 355 million years after the Big Bang, or about 2,57% of its current age.[10]
Discovery
GLASS-z12/GHZ2, was initially discovered as a robust z ≈ 12.0–12.5 candidate by Castellano et al. and Naidu et al. in the GLASS-JWST Early Release Science NIRCam field. The two discovery papers appeared on arXiv the same day. Hence these two names for this galaxy of GLASS-z12 (Naidu et al. 2022) and GHZ2 (Castellano et al. 2022a).[11]
GLASS-z12 derives its name from the GLASS survey that discovered it and its estimated photometric redshift of approximately z = 12.4+0.1 −0.3.[1] GLASS-z12 was initially announced as GLASS-z13 because it was thought to have a higher redshift of z = 13.1.[7][2] This redshift value was later revised down to z = 12.4 in October 2022, resulting in the renaming of this galaxy.[1]
It was discovered alongside another galaxy, GLASS-z10, comparable to GN-z11, also one of the oldest galaxies discovered.[12]
Color composite of JWST-NIRCam images showing GLASS-z12 as a red dot among other galaxies
Spectroscopy by the Atacama Large Millimeter Array
Spectroscopic observations of GLASS-z12 by the Atacama Large Millimeter Array (ALMA) in August 2022 confirmed that the galaxy has a spectroscopic redshift of 12.117±0.012, making it one of the earliest and most distant galaxies ever discovered, dating back to 360 million years after the Big Bang, 13.44 billion years ago.[12][5] ALMA observations detected an emission line associated with doubly ionized oxygen (O III) at 258.7 GHz with a significance of 5σ, suggesting that there is very low dust content in GLASS-z12, if not the early universe as well.[2] Also based on oxygen-related measurements, the age of the galaxy is confirmed.[13][14]
This galaxy was observed again in October 2023 by the James Webb Space Telescope with the NIRSpec and MIRI spectrographs, making it the most distant redshift galaxy of z = 12.34 with full spectroscopic coverage from ultraviolet (UV) to optical.[11][15]
According to current ΛCDM parameters (H0 = 67.4, Ωm = 0.315, ΩΛ = 0.685), this redshift of 12.34 corresponds to a light-travel distance (lookback time) of 13.44 billion years. However, due to the expansion of the universe, its comoving distance is 32.837 Gly.[16]
