XGAP with uGMRT I: Old AGN plasma in merging galaxy groups

TL;DR

The paper investigates AGN feedback in galaxy groups by combining uGMRT at 400 MHz, LOFAR at 144 MHz, and XMM-Newton X-ray data for three dynamically active X-GAP groups. It reveals extensive diffuse radio plasma around BGGs, with integrated spectral indices of $-0.96$, $-1.35$, and $-1.64$ and diverse spectral-index maps, indicating a range of ages and activity states. X-ray maps show elongated, merging IGrM halos, linking IGrM motions and environmental confinement to the observed radio morphologies and potential phoenix-like revival scenarios. Together, these results demonstrate how group-scale gas dynamics shape AGN feedback and the longevity of diffuse radio structures, justifying deeper multi-wavelength follow-up of the full X-GAP sample.

Abstract

Galaxy groups are affected by outflows from central Active Galactic Nuclei due to the shallower gravitational potential compared to galaxy clusters. The group binding energy is comparable to the energy output from AGN, making it an important factor in mutual evolution. We present a multi-wavelength analysis of three dynamically active groups: SDSSTG8102, SDSSTG16393, and SDSSTG28674, which are part of the XMM-Newton Group AGN Project X-GAP sample, a statistically complete sample of 49 galaxy groups. We combine uGMRT 400 MHz observations with 144 MHz LOFAR and XMM-Newton observations to study the radio sources associated with the Brightest Group Galaxies (BGGs). The BGGs in SDSSTG8102 and SDSSTG16393 have extended radio emission with asymmetric distortions in their morphologies. SDSSTG28674 has a compact flat-spectrum radio source associated with the BGG and an extended lobe on one side, connected by a faint bridge detected with LOFAR. Integrated spectral indices of the three BGGs are $-0.96\pm0.09$ (SDSSTG8102), $-1.35\pm0.09$ (SDSSTG16393), and $-1.6\pm0.02$ (SDSSTG28674). X-ray images reveal elongated morphologies in all three groups, with SDSSTG28674 showing evidence of a binary merger, while thermodynamical maps highlight temperature variations. In SDSSTG8102, lobes are bent and displaced by IGrM flows, while SDSSTG16393 hosts steep-spectrum relic-like plasma coinciding with X-ray emission. SDSSTG28674, with its ultra-steep spectrum lobe and disturbed morphology, likely traces merger-driven activity, consistent with a remnant or revived radio phoenix. The spectral diversity across the systems reflects different stages of AGN fading governed by duty cycle, source age, and confinement by the hot IGrM.

Figures (8)

• Figure 1: Left panel: The LOFAR (upper) and uGMRT (lower) surface brightness maps of SDSSTG8102 are shown in color, and the contours start with 3$\sigma_{\rm rms}$$\times$ [1,2,4,...], with $\sigma_{\rm rms} = 110\mu$Jy beam$^{-1}$ (at 144 MHz), and 30.5 $\mu$Jy beam$^{-1}$ (at 400 MHz) respectively. The green circle marks the BGG of the group. The white line in the lower image shows the location of the change in surface brightness. Middle panel: The radio surface brightness map for SDSSTG16393 (at 8$"$ resolution) is shown at both frequencies with a similar contour level as the upper panel, with rms values, $\sigma_{144 MHz} = 92 \mu$Jy beam$^{-1}$ (upper), $\sigma_{400 MHz} = 32 \mu$Jy beam$^{-1}$ (lower). Right panel: The same is shown for SDSSTG28674 (at 7$"$ resolution), with similar contour levels as the left panel with $\sigma_{144 MHz} = 85.1 \mu$Jy beam$^{-1}$ (upper), $\sigma_{400 MHz} = 28.7 \mu$Jy beam$^{-1}$ (lower).
• Figure 2: Left:The SDSS i-band image of the SDSSTG8102 is shown in colour (grey), and the overlaid magenta contours are from uGMRT 400 MHz, starting with 3$\sigma_{\rm rms}$$\times$ [1,2,4,...], where $\sigma_{\rm rms} = 30.5 \mu$Jy beam$^{-1}$. The green contours are from the VLASS 3.0 GHz image at 2$"$ resolution, where the contour levels are 3$\sigma_{\rm rms}$$\times$ [1,2,4], with $\sigma_{\rm rms}=108\mu$Jy beam$^{-1}$. The red circle indicates the BGG of the group. Middle: The same is shown for the SDSSTG16393, with the same contour level from uGMRT with an rms of 32$\mu$Jy beam$^{-1}$. The green contours are from the VLASS 3.0 GHz map. Right: The same is shown for the SDSSTG28674, with the same contour level as the upper panels, with an rms of 28.7$\mu$Jy beam$^{-1}$. The green contours are from the VLASS map, at a similar significance.
• Figure 3: Integrated spectrum of the central radio emission for each of the groups (at different colours) is shown between 144 MHz and 887 MHz. The dashed lines represent the fitted single power law. We have estimated the average flux density from a common region at each frequency for individual groups.
• Figure 4: Left: The spectral index map between 144 and 400 MHz is shown for SDSSTG8102. The overlaid black contours are from uGMRT 400 MHz, starting with 3$\sigma_{\rm rms}$$\times$ [1,2,4,...], where $\sigma_{\rm rms} = 30.5 \mu$Jy beam$^{-1}$, and the blue circle indicates the BGG of the group. middle: The spectral index map is shown for SDSSTG16393. The contour level is similar to the upper panel, and the $\sigma_{\rm rms} = 32 \mu$Jy beam$^{-1}$. Right: The same is shown for SDSSTG28674, having similar contour levels, with an $\sigma_{\rm rms} = 28.7 \mu$Jy beam$^{-1}$.
• Figure 5: Left: Adaptively smoothed 0.7 $-$ 1.2 keV image from the XMM-Newton is shown in color for SDSSTG8102, and the overlaid contours are from uGMRT 400 MHz, starting with 3$\sigma_{\rm rms}$$\times$ [1,2,4,...], with $\sigma_{\rm rms} = 30.5 \mu$Jy beam$^{-1}$. Middle: The same is shown for the SDSSTG16393 at 0.7 $-$ 1.2 keV range, with similar contour spacings, starting with an rms of 32$\mu$Jy beam$^{-1}$. The black strips are the chip gaps for the XMM-Newton CCDs. Right: The X-ray map is shown for the SDSSTG28674, with the same contour level as the previous panels, with an rms of 28.7$\mu$Jy beam$^{-1}$.