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This study examines 16 galaxy groups at redshifts between 1.6 and 3.6 to investigate how the temperature of gas flowing into dark matter halos affects whether galaxies stop forming stars. The researchers found that groups experiencing "hot accretion" (where inflowing gas is shock-heated) have approximately 50% of their galaxies in a quiescent, non-star-forming state, while groups with "cold accretion" show essentially no quiescent galaxies. In hot-accreting groups, massive quiescent galaxies are concentrated toward the center, and most groups lack a dominant central galaxy, suggesting they are still actively assembling rather than being mature systems.
Why it matters
These findings provide observational evidence that the transition from cold to hot gas accretion is a key driver in shutting down star formation in galaxies within groups. This suggests that environmental factors, rather than processes internal to individual galaxies, play the dominant role in determining whether galaxies remain active or become quiescent in these intermediate-mass cosmic structures.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: Cold accretion and quenching are closely related aspects of galaxy evolution, as sustained gas supply is required to maintain star formation. High-redshift galaxy groups therefore provide a valuable laboratory for testing how the thermal state of accreting gas relates to the emergence of quiescence. We measure quiescent fractions in a sample of 16 spectroscopically confirmed galaxy groups at $1.6<z<3.6$, spanning halo masses from $10^{12.8},{rm M_odot}$ to $10^{13.9},{rm M_odot}$, by fitting the SEDs of candidate member galaxies selected from the COSMOS2020 catalog and using a membership-probability approach to estimate group quiescent fractions. We compare these quiescent fractions to the expected cold or hot accretion state of each halo and find evidence for a correlation: quiescent fractions reach about 50 percent in groups in the hot-accretion regime and are consistent with zero in groups in the cold-accretion regime. In mature hot-accreting groups, massive quiescent galaxies are preferentially found in the inner regions ($R<0.5R_{rm vir}$), with a 4.4-sigma excess relative to the outskirts. Most groups lack a clearly established brightest group galaxy and instead show small stellar-mass gaps, typically $M_{*,1}/M_{*,2}<3$, indicating that they remain in an active assembly phase rather than being dynamically evolved systems. Consistently, the stellar-mass excess of the dominant galaxy, measured relative to the SHMR expectation, does not predict the group quiescent fraction. Taken together, our results support a picture in which the cold-to-hot transition in gas accretion contributes to the onset of quiescence, possibly through inside-out starvation associated with filament disruption in shock-heated intra-group gas, and suggest that environment plays a greater role than internal processes in shaping the quiescent galaxy population in these structures.
Source: Quiescent fractions in high-redshift galaxy groups reflect their hot-or-cold state of gas accretion