Evidence of sloshing-driven mini-halo formation in the cool-core cluster RXCJ1558.3-1410

TL;DR

This study analyzes RXCJ1558.3-1410 with Chandra X-ray data and multi-band uGMRT radio imaging to investigate the connection between thermal and non-thermal ICM components in a cool-core cluster. It identifies two X-ray cavities at SE and NW and a cold front at ~72 kpc caused by gas sloshing, and uncovers diffuse radio emission surrounding the BCG consistent with a mini-halo that is confined by the sloshing front. The authors argue that ICM sloshing-driven turbulence, rather than ongoing AGN jet activity, powers the mini-halo, supported by spatial correlations between the mini-halo edge, the cold front, and metallicity structure. They show the cavity power is sufficient to offset radiative cooling, linking AGN feedback and sloshing dynamics in maintaining the core’s thermal balance while driving non-thermal halo emission.

Abstract

Radio mini-halos are perplexing features, typically hosted by X-ray cool-core galaxy clusters. Understanding the connection between thermal X-ray and non-thermal radio emission is key to uncovering their origin. Here, we present a multiwavelength study of the cool-core cluster RXCJ1558.3-1410 using archival Chandra X-ray and wideband uGMRT radio data (Bands 3, 4 and 5). Our improved analysis confirms a previously known X-ray cavity at $\sim$36 kpc south-east of the cluster centre and we report a new cavity at $\sim$42 kpc to the north-west. These cavities suggest that the AGN provides mechanical power of $\sim$$6.0 \times 10^{44}$ erg s$^{-1}$, sufficient to offset radiative cooling in the ICM. We also detect a sharp surface brightness edge at $\sim$72 kpc south-east of the centre, characterised by a temperature jump and pressure continuity, consistent with a cold front, likely caused by gas sloshing from a minor merger. Our uGMRT images reveals an interesting diffuse emission surrounding the brightest cluster galaxy (BCG), with its edge spatially coinciding with the sloshing cold front and roughly with the cooling radius. Furthermore, a low star formation rate and uniform metal abundance up to the sloshing edge are consistent with the earlier findings of suppression of star formation and metallicity homogenisation by mixing core gas through sloshing. Finally, the spatial correlation between the mini-halo and the observed X-ray features indicates that ICM sloshing, rather than AGN feedback, plays a dominant role in powering the proposed radio mini-halo emission.

Figures (10)

• Figure 1: Left panel: 3$\times$ 3 exposure corrected, point sources removed, background subtracted 0.5 - 3.0 keV Chandra X-ray image of RXCJ1558 smoothed with a 2$\sigma$ Gaussian kernel. Inset close-up view of the cluster core, with X-ray substructures indicated by arrows and the BCG clearly marked. Right panel: 40$\times$ 40 Pan-STARRS1 r-band optical image of RXCJ1558 with BCG marked by a black arrow.
• Figure 2: Three-panel radio continuum observations of RXCJ1558 at different frequencies. Left to right: uGMRT Band 3 ($\sigma_{\rm rms}$ = 80 $\mu$Jy beam$^{-1}$), Band 4 ($\sigma_{\rm rms}$ = 130 $\mu$Jy beam$^{-1}$), and Band 5 ($\sigma_{\rm rms}$ = 41 $\mu$Jy beam$^{-1}$). The white contour levels are plotted at [3, 6, 12, 24, ...] $\times \sigma_{\rm rms}$ and a cyan dashed contour at -3$\sigma_{\rm rms}$. The synthesized beam size for each band is shown as a white box with black ellipse in the lower-right corner.
• Figure 3: (a): An unsharp-mask image of RXCJ1558 clearly shows NW and SE cavities. The image is overlaid with blue uGMRT Band 5 radio contours plotted at levels of $3\sigma \times (1, 3, 9, 27, \ldots)$ and negative $-3\sigma$ contours shown in green with $\sigma = 41~\mu$Jy beam$^{-1}$. (b): 3.8$\arcmin$$\times$ 3.8$\arcmin$ cropped 0.5-3 keV smoothed residual image of RXCJ1558 derived by subtracting the $\beta$-model, clearly discloses the clockwise sloshing structure in the ICM (black arrows), starting from cluster centre. This image is overlaid with blue contours of Band 3 plotted at $3\sigma \times (1, 2, 4, 8, \ldots)$, with $\sigma = 80~\mu$Jy beam$^{-1}$, and green contours shows negative $3\sigma$ level. (c): An unsharp mask image overlaid with different segments used to study the variation in counts at the cavity locations overlaid with Band 4 blue contours plotted at $\sigma \times (3, 6, 12, 24, \ldots)$. (d): A plot of the normalised counts versus sector number. The horizontal dashed blue line shows the average normalised counts without deviations.
• Figure 4: Upper left panel : A GGM filtered image of RXCJ1558 on a scale of 3$\sigma$. A cold front is apparent across Sector-I, marked by a cyan arc along with NW and SE cavities. Upper right panel : X-ray surface brightness profiles in the 0.5–3.0 keV energy band extracted along Sector-I. This profile was fitted with broken-power law density model shown in solid blue line. The insets in the panel show the corresponding 3D simulated gas density model. Lower panel : Thermodynamical profiles of temperature, metallicity, pressure, and electron density plotted as a function of radial distance. Green open diamonds and red crosses represent projected and deprojected profiles. The vertical blue dashed line indicates the location of the cold front.
• Figure 5: Upper panel: 2D temperature map (upper left), its error (upper right) of the ICM obtained from contour binning technique. Lower panel: 2D metallicity map (lower left) and its error (lower right). Colour bar in temperature and its error show in unit of keV. Colour bar in metallicity and its error show in the unit of Z$_{\odot}$. On both maps, uGMRT Band 3 radio contours are overlaid, and the cold front is marked by black dotted arc.