Large gas inflow driven by a matured galactic bar in the early Universe
Shuo Huang, Ryohei Kawabe, Hideki Umehata, Kotaro Kohno, Yoichi Tamura, Toshiki Saito
TL;DR
The paper demonstrates that a mature, fast bar can already exist in a gas-rich disk at $z=2.4669$, where bar-driven torques drive a large-scale gas inflow of about $579_{-174}^{+188}$ $M_\odot$ yr$^{-1}$ and sustain a central starburst. Using ALMA CO(4–3) and [CI](1–0) alongside VLA CO(1–0) data, the authors model the velocity field with circular and non-circular components to derive a pattern speed $\Omega_{\rm P}=67.5\pm17.2$ km s$^{-1}$ kpc$^{-1}$ and a corotation-to-bar length ratio $R_{\rm CR}/R_{\rm bar}\approx1.3$, indicating a fast bar. The galaxy exhibits a high baryon fraction within the disk, with $M_{mol}/M_*\approx0.69$ and $V_{rot}\approx640$ km s$^{-1}$, supporting a baryon-dominated, highly gas-rich environment that promotes rapid bar-driven secular evolution. Together, these results show that bar-driven gas transport and pseudobulge formation were already active more than 11 Gyr ago, providing crucial constraints for models of bar formation and disk evolution in the early Universe.
Abstract
Bar structures are present in about half of local disk galaxies and play pivotal roles in secular galaxy evolution. Bars impose a non-axisymmetric perturbation to the rotating disk and transport gas inward to feed central starburst and, possibly, the activity of the nuclear supermassive black hole. They are believed to be long-lived structures and are now identified at redshift $z>2$. Yet, little is known about the onset and effect of bars in the early cosmic epoch because spectroscopy of distant bars at sufficient resolution is prohibitively expensive. Here, we report a kinematic study of a galactic bar at redshift 2.467, 2.6 billion years after the Big Bang. We observe the carbon monoxide and atomic carbon emission lines of the dusty star-forming galaxy J0107a and find the bar of J0107a has gas distribution and motion in a pattern identical to local bars. At the same time, the bar drives large-scale non-circular motions that dominate over disk rotation, funneling molecular gas into its center at a rate of $\approx600$ solar masses per year. Our results show that bar-driven dynamical processes and secular evolution were already at play 11.1 billion years ago, powering active star formation amid the gas-rich and far-infrared luminous growth phase in a massive disk galaxy.