A Massive Rotating Disk in the Early Universe

Massive disk galaxies like the Milky Way are expected to form at late times in traditional models of galaxy formation, but recent numerical simulations suggest that such galaxies could form as early as a billion years after the Big Bang through the accretion of cold material and mergers. Observationally, it has been difficult to identify disk galaxies in emission at high redshift  to discern between competing models of galaxy formation. In this contribution, the authors report imaging, with a resolution of ~1.3 kiloparsecs, the 158-micrometre emission line from singly ionized carbon, the far-infrared dust continuum, and the near-ultraviolet continuum emission from a galaxy at a redshift of 4.2603, identified by detecting its absorption of quasar light. These observations show that the emission arises from gas inside a cold, dusty, rotating disk with a rotational velocity of ~ 272 kilometers per second. The detection of emission from carbon monoxide in the galaxy yields a molecular mass that is consistent with the estimate from the ionized carbon emission of ~ 72 billion M⊙. The existence of such a massive, rotationally supported, cold disk galaxy when the Universe was only 1.5 billion years old favors formation through either cold-mode accretion or mergers, although its large rotational velocity and large content of cold gas remain challenging to reproduce with most numerical simulations.

Figure caption: [Far left & left center]  VLA CO contours, and ALMA contours of the [CII] and thermal dust emission from the z=4.3 Wolfe galaxy.  [Right center & far right]: [CII] velocity field, and the rotation curve.

Publication: Marcel Neeleman (Max Planck Institute for Astronomy) et al., A Cold, Massive, Rotating Disk Galaxy 1.5 Billion Years after the Big Bang, Nature, 581, 269 (20 May 2020).

NRAO Press Release: ALMA Discovers Massive Rotating Disk in Early Universe

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