Source: a spectroscopic massive quiescent galaxy at z=7.29
Source: a spectroscopic massive quiescent galaxy at z=7.29
What is measured: JWST/NIRSpec/PRISM finds a strong Balmer break and no emission lines for RUBIES-UDS-QG-z7; redshift z=7.29 ±0.01. Modeling its spectrum with NIRCam and MIRI photometry yields stellar mass log10(M★/M☉)=10.23 ±0.04 within the adopted stellar-population model. The team infers most stars formed at z≈8–9 in a burst peaking around 100 solar masses a year before rapid quenching. It occupies roughly 300 arcmin² survey area and represents one object, not a measured high-precision population abundance.
What is disputed: Estimated number density log10(n/Mpc³)≈−5.8 (+0.5/−0.8) is >100× some simulations' prediction at z~7; one detection and assumptions about selection make the rate provisional. The authors’ acceptable fits span very different stellar metallicities, a warning about fitting systematics. Turner et al., 2025/26 FLARES analysis finds two simulated lookalikes and reports that systematics ease, but do not fully eliminate, the abundance discrepancy. Thus a challenge to early star-formation and quenching prescriptions is not automatically a demonstration of an impossible ΛCDM halo abundance. A follow-up ALMA [C II] measurement tests what ‘quiescent’ means physically.
Unlike some 2023 photometric extreme candidates, this object has a spectroscopic redshift and a Balmer-break spectrum; still distinguish fitted stellar mass from direct measurement. Return to the main question.