CFHT MegaCam Two Deep Fields Imaging Survey (2DFIS) II: Decoding the Lensing Profile of a "Rotating" Cluster with Deep CFHT Imaging

TL;DR

This study interrogates the rotating-cluster candidate RXCJ0110.0+1358 by combining deep CFHT weak-lensing imaging, SDSS spectroscopy, and XMM-Newton X-ray data. Despite a pronounced optical bimodality, weak-lensing mass reconstructions reveal a single dominant mass peak aligned with the BCG and X-ray emission in the southeast, while the northwestern peak has negligible mass, indicating a filament projection rather than rotation. A dual-halo lensing fit yields a primary halo of $\log(M_{200}/M_\odot)\approx14.00$ and a secondary halo of $\log(M_{200}/M_\odots)\approx13.1$, consistent with the kinematic substructure and explaining the previously claimed rotation as a projection effect and optical-group contamination. The results reconcile optical and X-ray views, show that the optical misclassification can inflate inferred halo mass, and demonstrate the necessity of multi-wavelength, model-based mass reconstructions for robust cluster dynamics. Overall, the cluster is best described as a Southeastern-dominant system with a filament-induced optical projection, not a coherently rotating halo.

Abstract

We present a multi-wavelength analysis of the galaxy cluster RXCJ0110.0+1358 ($z=0.058$), a rotating cluster candidate, combining deep CFHT imaging, SDSS photometry, spectroscopic redshifts, and XMM-Newton X-ray observations. We find a notable discrepancy between the optical and X-ray views: while optical data reveal a pronounced bimodal galaxy distribution with significant kinematic substructure signatures, the X-ray emission exhibits a single, smoothly extended component centered on the BCG. Our weak lensing analysis resolves this discrepancy by revealing that the mass is predominantly concentrated in the southeast ($\log M_{200}/M_\odot = 14.04_{-0.40}^{+0.24}$), while the northwestern substructure has a negligible mass ($\sim 10^{13} M_\odot$). This immense mass disparity rules out the dynamical possibility of a rotating system. We demonstrate that the apparent optical bimodality arises from the projection of a filament, which led optical group-finding algorithms to misclassify these galaxies as cluster members. This contamination creates a spurious substructure that mimics a rotation signal and leads to an overestimation of the luminosity-based halo mass, resolving the observed inconsistencies.

Figures (11)

• Figure 1: XMM-Newton image in the 0.5-2.0 keV band. Dashed contours show the optical $r$-band galaxy luminosity.
• Figure 2: Results of the substructure test. The top and bottom rows correspond to Case 1 (all members) and Case 2 spectroscopic members only), respectively. Left panels: Spatial distribution of the $\delta$ statistic. The radius of each circle scales with $\mathrm{e}^{\delta_i}$. Blue contours trace the galaxy luminosity map, and the red cross marks the luminosity-weighted center. Right panels: Distribution of the cumulative $\Delta_\mathrm{sim}$ statistic derived from Monte Carlo realizations. The vertical red line indicates the observed $\Delta$ value calculated from the data.
• Figure 3: MP17 rotation analysis results for Case 1 (top row; all 71 members) and Case 2 (bottom row; 56 spectroscopic members). Left: Member galaxy distribution (black circle) with the best-fit rotation axis (green solid line). Second column: Rotation curves ($\Delta \bar{v}_\mathrm{los}$). Black dots: observed data; Blue curve: best-fit sinusoidal model; Red curve: ideal rotation profile; Gray curve/shading: random realizations with $1\sigma$ scatter. Third column: KS two-sample test $p$-values. The red dashed line indicates $p=0.01$; the green line marks the best-fit axis angle. Right: Histograms of line-of-sight velocities.
• Figure 4: Properties of the member galaxies. Left panel: Magnitude - Color diagram. Right panel: Spatial distribution. In both panels, members associated with the northwestern and southeastern components are shown in orange and gray, respectively. Black hollow squares denote galaxies with redshifts estimated using the nearest-neighbor method.
• Figure 5: Residuals of ellipticity and size between PSF model and PSF star.