Multiphase gas offsets in the atmospheres of central galaxies and their consequences for SMBH activation I. The hot and warm ionized gas phases

TL;DR

This study tackles how multiphase gas offsets in cool-core groups and clusters relate to SMBH fueling. By combining Chandra X-ray, VLT/MUSE Hα, and pc-scale VLBA observations, it shows that hot-gas peaks are commonly offset from the SMBH (⟨Δ^{SMBH}_{X-ray}⟩ ≈ 4.8 kpc), while warm Hα peaks stay tightly associated with the SMBH (⟨Δ^{SMBH}_{Hα}⟩ ≈ 0.6 kpc). Crucially, systems with Hα peak–SMBH offsets ≥1 kpc lack detectable pc-scale radio cores (P_{5 GHz} ≤ 10^{21–22} W Hz^{-1}), suggesting that centrally concentrated warm gas enables cold-mode accretion and jet activity (in contrast to hot-gas–driven feeding). The offsets indicate a fragmented cooling-core environment where warm gas offsets develop over ~10–70 Myr, and the observed dynamics point to a scenario in which warm gas detaches from hot gas after condensation, with implications for AGN fueling and feedback. The authors plan to extend this analysis to the molecular phase (paper II) and advocate for next-generation high-resolution X-ray observatories to continue mapping multiphase gas and SMBH fueling.

Abstract

We investigate the spatial relationships between multi-phase gas components and supermassive black hole (SMBH) activity in a sample of 25 cool core galaxy groups and clusters. Using high angular resolution observations from \textit{Chandra}, VLT/MUSE, and VLBA, we robustly locate the position, respectively, of the X-ray peak of the intracluster medium (ICM), of the H$α$ peak of the warm ionized gas, and of the SMBH radio core on parsec scales. We identify spatial offsets between the X-ray peak of the hot gas and the SMBH in 80% of the systems, with an average displacement of $\langleΔ^{\text{SMBH}}_{\text{X-ray}}\rangle = 4.8$ kpc (dispersion of $3.8$ kpc). In contrast, the peak of warm ionized gas traced by H$α$ exhibits much smaller offsets ($\langleΔ^{\text{SMBH}}_{\text{H}α}\rangle = 0.6$ kpc; dispersion of $1.4$ kpc) and a lower incidence of displacement (15%). Our findings suggest that hot gas sloshing primarily drives the observed spatial offsets, with AGN-driven uplift contributing in some systems.Importantly, systems with H$α$ - SMBH offsets of $\geq$1 kpc uniformly lack detectable radio cores on VLBA scales, with upper limits on the 5~GHz power of $P_{5\,\text{GHz}} \leq 10^{21-22}$ W Hz$^{-1}$, while those without such offsets exhibit radio powerful AGN with pc-scale radio emission up to $P_{5\,\text{GHz}} \sim 10^{24-25}$ W Hz$^{-1}$. This correlation indicates that centrally concentrated warm gas is critical for sustaining radio-loud SMBH activity, possibly supporting scenarios of cold-mode accretion. Overall, our results highlight the importance of high-angular-resolution, multi-wavelength observations for understanding the interplay between multiphase gas cooling and AGN fueling in central galaxies.

Figures (9)

• Figure 1: The link between multiphase gas offsets and SMBH activation. Left: Radio power at 5 GHz (from pc-scale VLBA radio observations) of the 25 BCGs in our sample vs the distance between the position of the SMBH and of the hot gas peak (from X-ray emission in Chandra data). Right: Radio power at 5 GHz vs the distance between the position of the SMBH and of the warm gas peak (from the H$\alpha$ emission line in VLT/MUSE data). In both panels, empty points represent systems with significant offsets (that is, for which the distance $\Delta$ between the SMBH and the gas peak is larger than the uncertainty $\delta\Delta$), and arrows represent upper limits on the radio power.
• Figure 2: Multiwavelength view of the four systems with a significant H$\alpha$ peak - SMBH offset. The panels show smoothed X-ray Chandra maps of the hot gas, with grayscale contours of the H$\alpha$ line from MUSE data. The red square marks the position of the X-ray peak, the purple circle shows the location of the H$\alpha$ peak, and the black star shows the position of the SMBH (see Tab. \ref{['tab:completeinfo']}).
• Figure 3: Multiwavelength view of the systems in our sample. The panels show smoothed X-ray Chandra maps of the hot gas, with grayscale contours of the H$\alpha$ line from MUSE data. The red square marks the position of the X-ray peak, the purple circle shows the location of the H$\alpha$ peak, and the black star shows the position of the SMBH (see Tab. \ref{['tab:completeinfo']}). When detected, the VLBA image of the pc-scale radio core is shown in the insets.
• Figure 4: Continued.
• Figure 5: Left: Comparison between the SMBH - H$\alpha$ peak offset with the SMBH - X-ray peak offset; the dashed line marks the line of 1:1 scaling between the two distances. Right: Velocity of the warm gas, measured from the MUSE data within an extraction region centered on the H$\alpha$ peak with radius 1.8 kpc, versus the SMBH–H$\alpha$ peak offset. Dashed lines show the time required to traverse the distance on the x-axis at various (constant) velocities on the y-axis. For example, the brown line indicates that for a velocity of 50 km/s, the time needed to travel a distance of 6 kpc is approximately 100 Myr. Thus, depending on the warm gas velocity and the offset of the H$\alpha$ peak from the SMBH, each system lies along a different crossing time line.