Longevity of dynamically cold high-redshift discs

Determine whether the highest observed V/σ values in dynamically cold, massive high-redshift galaxies correspond to transient phases or whether such discs can persist while experiencing mergers, gas-accretion events, and strong feedback.

Background

REBELS-25 exhibits strong rotational support in both warm ionised gas and colder neutral gas at z=7.31. Comparisons with simulations indicate that some dynamically cold discs may be short-lived, whereas others may persist for several hundred million years.

The authors explicitly leave unresolved whether the extreme rotational support observed in systems such as REBELS-25 is a temporary evolutionary state or a durable configuration compatible with continued assembly and feedback.

References

However, it remains unclear whether the highest observed $V/\sigma$ values correspond to relatively transient phases of the most massive systems, and to what extent such dynamically cold discs can survive mergers, gas accretion events, and strong feedback at early times.

— REBELS-25: multi-phase morphology and kinematics at z = 7.31  (2608.25982 - Rowland et al., 26 Aug 2026) in Section 5.2, Multi-phase gas kinematics