The RESOLVE and ECO G3 Initiative: Drivers of HI Content and X-ray Emission in Galaxy Groups

Abstract

Adding to the RESOLVE and ECO Gas in Galaxy Groups (G3) initiative, we examine possible drivers of group-integrated HI-to-halo mass ratios ($M_{\mathrm{HI},\mathrm{grp}}/M_{\mathrm{halo}}$) and group X-ray emission, including group halo mass ($M_{\mathrm{halo}}$), virialization as probed by crossing time ($t_{\mathrm{cross}}$), presence of active galactic nuclei (AGN), and group-integrated fractional stellar mass growth rate (FSMGR${}_{\mathrm{grp}}$). G3 groups span $M_{\mathrm{halo}}=10^{11-14.5}{M}_{\odot }$ with comprehensive HI 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 $M_{\mathrm{halo}}=10^{12.6-14}{M}_{\odot }$ and unambiguously for $M_{\mathrm{halo}}>10^{14}{M}_{\odot }$, reflecting an inverse dependence of $M_{\mathrm{HI},\mathrm{grp}}/M_{\mathrm{halo}}$ and hot gas emission on halo mass. At fixed halo mass, $M_{\mathrm{HI},\mathrm{grp}}/M_{\mathrm{halo}}$ transitions to greater spread below $t_{\mathrm{cross}}\sim 2$ Gyr. Dividing groups across this transition, lower-$t_{\mathrm{cross}}$ groups show elevated X-ray emission compared to higher-$t_{\mathrm{cross}}$ groups for $M_{\mathrm{halo}}>10^{13.3}{M}_{\odot }$, but this trend reverses for $M_{\mathrm{halo}}=10^{12.6-13.3}{M}_{\odot }$. Additionally, AGN-hosting halos below $M_{\mathrm{halo}}\sim 10^{12.1}{M}_{\odot }$ exhibit a broad, $\sim$0.25 dex deep valley in $M_{\mathrm{HI},\mathrm{grp}}/M_{\mathrm{halo}}$ compared to non-AGN-hosting halos with correspondingly reduced FSMGR${}_{\mathrm{grp}}$. When diluted by non-AGN-hosting halos, this valley becomes shallower and narrower, falling roughly between $M_{\mathrm{halo}}=10^{11.5}{M}_{\odot }$ and $M_{\mathrm{halo}}=10^{12.1}{M}_{\odot }$ in the overall $M_{\mathrm{HI},\mathrm{grp}}/M_{\mathrm{halo}}$ vs. $M_{\mathrm{halo}}$ relation. We may also detect a second, less easily interpreted valley at $M_{\mathrm{halo}}\sim 10^{13}{M}_{\odot }$. Neither valley matches theoretical predictions of a deeper valley at or above $M_{\mathrm{halo}}=10^{12.1}{M}_{\odot }$.

23 pages, 11 figures. Accepted to ApJ