The effect of dynamical states on galaxy clusters populations. II. Comparison of galaxy properties and fundamental relations

TL;DR

The paper investigates how the dynamical state of massive galaxy clusters affects member galaxies and their fundamental relations at low redshift ($0.10 < z < 0.35$) using a mass-matched sample of relaxed and disturbed clusters. It employs multi-band photometry, SED fitting, and both nonparametric and parametric morphology analyses to derive stellar mass, sSFR, sizes, and structural parameters, comparing the two dynamical states. The main finding is that the dynamical state does not significantly alter fundamental relations such as color-magnitude, mass-size, morphology-density, or SF-density, but it does influence higher-order moments of the distributions, notably in low-mass and red-sequence galaxies, implying subtle environmental imprints from disturbed clusters. These results support a scenario where primary galaxy evolution is set by early pre-processing, with later cluster dynamics leaving measurable, though modest, signatures in the tails of property distributions. Overall, the study highlights the resilience of key galaxy-cluster relations while revealing nuanced environmental effects tied to cluster dynamical activity.

Abstract

Galaxy clusters provide a unique environment to study galaxy evolution. The role of cluster dynamical states in shaping the physical and morphological properties of member galaxies remains an open question. We aim to assess the impact of the dynamical state of massive ($M_{500} \geq 1.5 \times 10^{14} M_{\odot}$) galaxy clusters on the physical and structural properties of their member galaxies, and also in their fundamental relations in the redshift range $0.10 < z < 0.35$. We use a mass-matched sample of galaxies from relaxed and disturbed clusters. Morphological types were assigned using both parametric and nonparametric methods, while physical properties were derived through SED fitting. Galaxies were further divided into subpopulations to investigate trends with cluster dynamical states. The dynamical state of galaxy clusters does not alter their fundamental relations at low redshift (such as color-magnitude, mass-size, morphology-density, and SF-density relations), nor does it significantly affect the mean or dispersion of galaxy properties. However, it does impact the distributions at the level of third- and fourth-order moments, introducing asymmetries and heavier tails in the properties of galaxies. The greatest effects are observed in the sSFRs of low-mass and red sequence galaxies. These findings suggest that, at low redshift, the fundamental relations of massive galaxy clusters are already well established and resilient to recent dynamical activity. Nonetheless, the influence of the dynamical state on the higher-order moments of galaxy properties indicates that environmental processes associated with disturbed clusters still leave measurable imprints, particularly on low-mass and red sequence galaxies. This is consistent with the idea that galaxy evolution is shaped both by early pre-processing and by subsequent interactions within dynamically active environments.

Figures (19)

• Figure 1: Example of the Galfitm output for the bulge-dominated galaxy J002712.03-343901.38 belonging to the Abell 2715 galaxy cluster, with a Sérsic index value of $n_r = 2.527 \pm 0.079$. The residual image corresponds to the difference between the observed image and the fitted model.
• Figure 2: Example of the Galfitm output for the disk-dominated galaxy J220241.77-600131.8, belonging to the Abell 3827 galaxy cluster, with a Sérsic index value of $n_r = 0.984 \pm 0.010$.
• Figure 3: Principal components (PC 1 and PC 2) of the morphological parameters $G$ and $M_{20}$ for approximately 17,000 galaxies. A hexagonal binning has been applied with a grid size of (30, 9), considering only bins containing at least 20 data points. The horizontal dashed white line corresponds to the main sequence in this plane, and the shaded regions in dark and light blue correspond to the 1$\sigma$ and 2$\sigma$ zones, respectively. The hexbins follow a color map associated with three different variables. From left to right, we have: the Sérsic index, $n$, asymmetry, $A$, and S/N.
• Figure 4: Color distribution of all galaxies after applying the quality cuts (Section \ref{['sec:quality-cuts']}). Dashed blue and red curves correspond to the Gaussian models fitted to the blue and red component, respectively, while the solid black curve is the sum of both. The vertical dashed black line is the color threshold to separate star-forming blue and passive red galaxies, selected as the minimum value between the two peaks, $(g-r)_{\text{norm}} = -0.3$.
• Figure 5: Distribution of bulge galaxies (red contours) and disk galaxies (blue contours) in the mass-size logarithmic space, separated into relaxed and disturbed clusters. The solid lines show the linear regressions applied to the data (following the same color code), and the text indicates the slopes with their respective errors for each galaxy population.