Insufficient Gas Accretion Caused the Decline in Cosmic Star-Formation Activity 8 Billion Years Ago

Abstract

Measurements of the atomic hydrogen (HI) properties of high-redshift galaxies are critical to understanding the decline in the star-formation rate (SFR) density of the Universe after its peak $\approx 8-11$ Gyr ago. Here, we use $\approx 510$ hours of observations with the upgraded Giant Metrewave Radio Telescope to measure the dependence of the average HI mass of star-forming galaxies at $z=0.74-1.45$ on their average stellar mass and redshift, by stacking their HI 21 cm emission signals. We divide our sample of 11,419 main-sequence galaxies at $z=0.74-1.45$ into two stellar-mass ($M_{\ast }$) subsamples, with $M_{\ast }>10^{10}{M}_{\odot }$ and $M_{\ast }<10^{10}{M}_{\odot }$, and obtain clear detections, at $>4.6\sigma$ significance, of the stacked HI 21 cm emission in both subsamples. We find that galaxies with $M_{\ast }>10^{10}{M}_{\odot }$, which dominate the decline in the cosmic SFR density at $z\lesssim 1$, have HI reservoirs that can sustain their SFRs for only a short period, $0.86\pm 0.20$ Gyr, unless their HI is replenished via accretion. We also stack the HI 21 cm emission from galaxies in two redshift subsamples, at $z=0.74-1.25$ and $z=1.25-1.45$, again obtaining clear detections of the stacked HI 21 cm emission signals, at $>5.2\sigma$ significance in both subsamples. We find that the average HI mass of galaxies with $⟨M_{\ast }⟩\approx 10^{10}{M}_{\odot }$ declines steeply over a period of $\approx 1$ billion years, from $(33.6\pm 6.4)\times 10^9{M}_{\odot }$ at $⟨z⟩\approx 1.3$ to $(10.6\pm 1.9)\times 10^9{M}_{\odot }$ at $⟨z⟩\approx 1.0$, i.e. by a factor $\gtrsim 3$. We thus find direct evidence that accretion of HI onto star-forming galaxies at $z\approx 1$ is insufficient to replenish their HI reservoirs and sustain their SFRs, thus resulting in the decline in the cosmic SFR density 8 billion years ago.

arXiv comment11 Pages, 7 Figures; Astrophysical Journal Letters, 931 L34; a minor typographical error is fixed in this version

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Cited by in corpus (7)

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• Atomic Gas Scaling Relations of Star-forming Galaxies at $z\approx 1$
• Atomic Gas Dominates the Baryonic Mass of Star-forming Galaxies at $z\approx 1.3$
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