The RESOLVE and ECO G3 Initiative: Drivers of H i Content and X-Ray Emission in Galaxy Groups

Journal article, 2025

Adding to the RESOLVE and ECO Gas in Galaxy Groups (G3) initiative, we examine possible drivers of group-integrated H i-to-halo mass ratios (MHI,grp/Mhalo) and group X-ray emission, including group halo mass (Mhalo), virialization as probed by crossing time (tcross), presence of active galactic nuclei (AGN), and group-integrated fractional stellar mass growth rate (FSMGRgrp). G3 groups span Mhalo = 10¹¹−10^14.5 M⊙ with comprehensive H i gas and AGN information, which we combine with X-ray stacking of ROSAT All-Sky data. We detect hot gas emission exceeding AGN and X-ray binary backgrounds confidently for Mhalo = 10^12.6−10¹⁴ M⊙ and unambiguously for Mhalo > 10¹⁴ M⊙, reflecting an inverse dependence of MHI,grp/Mhalo and hot gas emission on halo mass. At fixed halo mass, MHI,grp/Mhalo transitions to greater spread below tcross ∼ 2 Gyr. Dividing groups across this transition, lower-tcross groups show elevated X-ray emission compared to higher-tcross groups for Mhalo > 10^13.3 M⊙, but this trend reverses for Mhalo = 10^12.6−10^13.3 M⊙. Additionally, AGN-hosting halos below Mhalo ∼ 10^12.1 M⊙ exhibit a broad, ∼0.25 dex deep valley in MHI,grp/Mhalo compared to non-AGN-hosting halos with correspondingly reduced FSMGRgrp. When diluted by non-AGN-hosting halos, this valley becomes shallower and narrower, falling roughly between M halo = 10 11.5 M ⊙ and M halo = 10 12.1 M ⊙ in the overall MHI,grp/Mhalo vs. Mhalo relation. We may also detect a second, less easily interpreted valley at Mhalo ∼ 10¹³ M⊙. Neither valley matches theoretical predictions of a deeper valley located at or above M halo = 10 12.1 M ⊙ .