| GLASS-z12 | |
|---|---|
|   Close-up view of GLASS-z12 from the James Webb Space Telescope  | |
| Observation data (J2000 epoch) | |
| Constellation | Sculptor | 
| Right ascension | 00h 13m 59.76s [1] | 
| Declination | −30° 19′ 29.1″ [1] | 
| Redshift | 12.117±0.012 (spectroscopic) [2] 12.4+0.1 −0.3 [1] 12.42+0.27 −0.14 [3] 12.28+0.08 −0.07 [4] | 
| Distance | 
 | 
| Apparent magnitude (V) | 27.0 AB (F200W) [1] | 
| Characteristics | |
| Mass | ≈1.0×109 M☉ | 
| Size | ~3000 ly (1 kpc) | 
| Half-light radius (physical) | 500 pc | 
| Other designations | |
| GHZ2 [6] [7] ·GLASS-17487 [3] | |
| References:  [1]  | |
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]
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]
 
 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]
GLASS-z12 has a light-travel distance (lookback time) of 13.4 billion years. [5] However, due to the expansion of the universe, its present proper distance is 32.718 billion light-years. [5]
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]