Widespread Inflows Reveal Baryonic Cycling in Star-forming and Quiescent Galaxies
Abstract
Cool-gas inflows, required to sustain star formation, have been fundamental in simulations yet remained observationally elusive. Using DESI spectroscopy of ~30,000 galaxies, we identify coherent inflowing gas (~100 km/s) in 20-50% of the sample, yielding a population-level census of gas flows. We uncover a striking inversion: inflows are detected in quiescent galaxies, whereas star-forming systems are dominated by gravitationally bound outflows. At fixed age, galaxies with inflows, outflows, or no/weak flows share similar masses, environments, and structures, indicating that these properties do not differentiate flow states. Instead, gas-flow state is linked to stellar population age and recent evolutionary history, consistent with age-dependent gas flows in two regimes. In some star-forming galaxies, elevated star formation surface densities drive outflows that recycle on ~0.5 Gyr timescales, consistent with a galactic fountain. In quiescent systems, low-level ``drizzling'' inflows persist, consistent with slowly cooling enriched halo gas and weak radio-mode nuclear activity. Broad gas-phase metallicity distributions---and absence of a pristine dilution signature---indicate that detected inflows are predominantly recycled or enriched. Detectability is modulated by dust, ionization, and geometry: in star-forming disks, inflowing gas lies near the disk plane and is obscured or ionized, while outflow hosts exhibit higher dust and metal content. As star formation declines, cold-outflow signatures weaken, and recycled or slowly cooling gas is more readily detected as inflow. Post-starburst galaxies provide snapshots of this transition. Our results resolve the scarcity of observed inflows, provide evidence for widespread gas accretion and recycling in present day galaxies, and establish an observational framework linking gas flows to star formation, chemical evolution, and galaxy structure.
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BibTeX
@misc{yesuf2026widespread,
title = {{Widespread Inflows Reveal Baryonic Cycling in Star-forming and Quiescent Galaxies}},
author = {Hassen M. Yesuf and Ravi Joshi and Yuxuan Zou and Feng Yuan and Luis C. Ho and Lin Lin and Lei Hao and Shiyin Shen and Connor Bottrell and Fulai Guo and John D. Silverman},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.04327},
eprint = {2609.04327},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.04327},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Widespread Inflows Reveal Baryonic Cycling in Star-forming and Quiescent Galaxies
AU - Hassen M. Yesuf
AU - Ravi Joshi
AU - Yuxuan Zou
AU - Feng Yuan
AU - Luis C. Ho
AU - Lin Lin
AU - Lei Hao
AU - Shiyin Shen
AU - Connor Bottrell
AU - Fulai Guo
AU - John D. Silverman
PY - 2026
DA - 2026/09/03
PB - arXiv
DO - 10.48550/arxiv.2609.04327
UR - https://arxiv.org/abs/2609.04327
AB - Cool-gas inflows, required to sustain star formation, have been fundamental in simulations yet remained observationally elusive. Using DESI spectroscopy of ~30,000 galaxies, we identify coherent inflowing gas (~100 km/s) in 20-50% of the sample, yielding a population-level census of gas flows. We uncover a striking inversion: inflows are detected in quiescent galaxies, whereas star-forming systems are dominated by gravitationally bound outflows. At fixed age, galaxies with inflows, outflows, or no/weak flows share similar masses, environments, and structures, indicating that these properties do not differentiate flow states. Instead, gas-flow state is linked to stellar population age and recent evolutionary history, consistent with age-dependent gas flows in two regimes. In some star-forming galaxies, elevated star formation surface densities drive outflows that recycle on ~0.5 Gyr timescales, consistent with a galactic fountain. In quiescent systems, low-level ``drizzling'' inflows persist, consistent with slowly cooling enriched halo gas and weak radio-mode nuclear activity. Broad gas-phase metallicity distributions---and absence of a pristine dilution signature---indicate that detected inflows are predominantly recycled or enriched. Detectability is modulated by dust, ionization, and geometry: in star-forming disks, inflowing gas lies near the disk plane and is obscured or ionized, while outflow hosts exhibit higher dust and metal content. As star formation declines, cold-outflow signatures weaken, and recycled or slowly cooling gas is more readily detected as inflow. Post-starburst galaxies provide snapshots of this transition. Our results resolve the scarcity of observed inflows, provide evidence for widespread gas accretion and recycling in present day galaxies, and establish an observational framework linking gas flows to star formation, chemical evolution, and galaxy structure.
ER -