Statistical Properties of Cold Streams in Massive Star-forming Halos in TNG50

Abstract Cold, dense streams of gas are predicted to penetrate deeply into massive (≳10 12 M ⊙ ) halos at cosmic noon ( z ∼ 4–2), fueling galaxies to sustain high star formation rates. We investigate the prevalence of such cold streams in TNG50 over the range z = 4–0, using a novel algorithm to automatically detect cold streams in simulated halos. We qualitatively and quantitatively characterize the geometric and physical properties of the detected streams over cosmic time. We find that cold streams are ubiquitous in massive halos at cosmic noon, occurring in >80% of such systems down to z = 1, before becoming rare by z = 0. At their peak prevalence ( z = 2–1), streams are often found in roughly coplanar, three-stream configurations. These streams generally exhibit a dense and cool core, surrounded by a diffuse and warmer envelope. However, we find that, in TNG50, these streams typically disrupt in the outer halo and do not penetrate efficiently to the central galaxy, with the total mass inflow from streams peaking at z = 2. Our results underscore the importance of cold streams in fueling galaxies at early times, but they highlight the need for higher-resolution simulations to fully capture their survival and impact at later epochs. Future cosmological zoom-in simulations, with better resolution in the CGM, will be essential to resolve turbulent mixing layers and feedback–inflow interactions that determine whether cold streams can reach the galactic disk.