مجرة عملاقة من الكون الفتي سريع

الملخص الأصلي

كما كتبه المؤلفون، بالإنجليزية arXiv:2604.07440

Recent JWST observations revealed two massive ($$M_{\star} \gtrsim 10^{11}\,M_{\odot}$$), unexpectedly large spiral galaxies at $$z \sim 3$$, both in overdense environments. We focus on one of these, ADF22.1 at $$z = 3.09$$, which hosts an active galactic nucleus (AGN), exploiting its extended [CII] emission ($$\sim$$30 kpc in diameter) with high-resolution observations from the Atacama Large Millimetre Array and JWST. We find a flat outer rotation curve reaching $$\sim$$530 km s$$^{-1}$$, and perform, for the first time for a system of this type, a rotation-curve decomposition. We infer a dark-matter halo mass of $$\log(M_{200}/M_{\odot})=12.9^{+0.4}_{-0.3}$$, a baryon-to-halo mass ratio of $$0.4^{+0.6}_{-0.3}$$ in units of the cosmological baryon fraction, and a ratio between the baryonic and dark-matter halo specific angular momentum of $$1.0^{+0.7}_{-0.5}$$. Comparing these quantities with those of local galaxies, we find that ADF22.1 is indistinguishable from $$z=0$$ giant discs, pointing to the inefficiency of AGN feedback in halting disc growth. Using the Mapping Nearby Galaxies at Apache Point Observatory survey, we identify potential $$z=0$$ descendants of ADF22.1, suggesting it will evolve into an extreme (in either mass or angular momentum) early-type galaxy. Finally, we argue that cold-stream accretion, invoked to explain disc formation at $$z > 1$$, cannot simultaneously account for its size, dynamical properties, high specific angular momentum, and baryon-to-halo mass ratio. Instead, sustained accretion from the hot circumgalactic medium, either via spontaneous or fountain-driven condensation, offers a more physically plausible formation pathway.