Speaker
Description
Understanding the stellar mass build-up and evolution of the surprisingly massive galaxies in the Epoch of Reionization (EoR) requires insight into their molecular gas reservoirs, which fuel star formation. I will present new deep VLA observations of REBELS-25 (z = 7.31), a massive star-forming galaxy and the highest-redshift dynamically cold disk (V_rot,max/σ ≃ 11) confirmed to date. Using ~40 hours of VLA observations, we detect CO(3-2) line emission, providing the first direct measurement of the cool molecular gas in a star-forming galaxy at z > 7. The measured line flux translates to a CMB-corrected molecular gas mass of (1.3 ± 0.7) × 10¹¹ M_sun, indicating that REBELS-25 hosts a massive molecular gas reservoir already ~700 Myr after the Big Bang. We also derive a high gas fraction of ~95% and a depletion time of ~0.65 Gyr. The latter is consistent with extrapolated trends from significantly lower-redshift main-sequence galaxies. We find that the CO- and [CII]-based gas masses are consistent within 1σ, supporting the use of [CII] as a gas-mass tracer for star-forming galaxies in the EoR.
Additionally, recently obtained ALMA data allow us to detect CO(7-6) emission, providing constraints on the excitation ratio and ISM properties through detailed modeling. Upcoming JWST NIRCam grism observations will further enable us to study ionized gas kinematics via [OIII] λ5007 and compare it to the cool gas dynamics traced by [CII]. This will test whether the extreme rotational support seen in [CII] is consistent with the warm ionized gas, shedding light on how rotationally supported systems form so rapidly.
These results highlight the detectability of low-J CO emission even at z>7, paving the way for next-generation instruments, and stress the importance of the synergy between different facilities in providing critical insights into the rapid mass assembly of massive galaxies during the first billion years of cosmic history.
| Talk category | NOVA Network 1 |
|---|---|
| Preference for a talk or poster | Talk |
| Talk preference for PhD students | First year |
