Starbursts with suppressed velocity dispersion revealed in a forming cluster at z=2.51

Abstract

One of the most prominent features of galaxy clusters is the presence of a dominant population of massive ellipticals in their cores. Stellar archaeology suggests that these gigantic beasts assembled most of their stars in the early Universe via starbursts. However, the role of dense environments and their detailed physical mechanisms in triggering starburst activities remain unknown. Here we report spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of the CO $J=3-2$ emission line, with a resolution of about 2.5 kiloparsecs, toward a forming galaxy cluster core with starburst galaxies at $z=2.51$. In contrast to starburst galaxies in the field often associated with galaxy mergers or highly turbulent gaseous disks, our observations show that the two starbursts in the cluster exhibit dynamically cold (rotation-dominated) gas-rich disks. Their gas disks have extremely low velocity dispersion (${\sigma }_0\sim 20-30$ km s${}^{-1}$), which is three times lower than their field counterparts at similar redshifts. The high gas fraction and suppressed velocity dispersion yield gravitationally unstable gas disks, which enables highly efficient star formation. The suppressed velocity dispersion, likely induced by the accretion of corotating and coplanar cold gas, might serve as an essential avenue to trigger starbursts in massive halos at high redshifts.

19 pages, 14 figures, 3 tables. Accepted for publication in A&A

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Cited by in corpus (8)

• The ALMA-ALPAKA survey I: high-resolution CO and [CI] kinematics of star-forming galaxies at z = 0.5-3.5
• Cold gas disks in main-sequence galaxies at cosmic noon: Low turbulence, flat rotation curves, and disk-halo degeneracy
• VLA Legacy Survey of Molecular Gas in Massive Star-forming Galaxies at High Redshift
• JWST's first glimpse of a z > 2 forming cluster reveals a top-heavy stellar mass function
• Accelerated structural evolution of galaxies in a starbursting cluster at z=2.51
• Unveiling dust, molecular gas, and high star formation efficiency in extremely UV bright star-forming galaxies at $z\sim 2.1-3.6$
• Observational biases on rotation curves from IFU data at cosmic noon
• Ram-pressure stripping caught in action in a young cluster at $z=2.51$