K-DRIFT Science Theme: New Theoretical Framework Using the Galaxy Replacement Technique for LSB studies

Abstract

Low-surface-brightness (LSB) structures provide critical insights into the hierarchical formation of galaxies and galaxy clusters. The KASI Deep Rolling Imaging Fast Telescope (K-DRIFT) is designed to detect such diffuse features through deep, wide-field optical imaging with a surface brightness reaching $\sim$$30~\rm{mag}~\rm{arcsec}^{-2}$. To interpret the observation data expected from K-DRIFT, we have developed the Galaxy Replacement Technique (GRT), an $N$-body simulation framework optimized for tracing the gravitational evolution of stellar components. The GRT works by inserting high-resolution galaxy models, including a dark matter (DM) halo and stellar disk, in place of multiple low-resolution DM halos in the base $N$-body cosmological simulation. It allows us to achieve very high mass ($m_{star}=5.4\times10^4\msun\ h^{-1}$) and spatial resolution (10~$\rm{pc}~h^{-1}$) with shorter computation time compared to full hydrodynamic cosmological simulations. Therefore, this technique is particularly well-suited for studying LSB structures, with a surface brightness reaching $\sim$$31~\rm{mag}~\rm{arcsec}^{-2}$. In this paper, we present the motivation and methodology of the GRT, summarize key results from previous studies, and highlight its synergy with K-DRIFT observations. We further discuss planned science cases using the GRT, aiming to build a theoretical basis for interpreting LSB features in various environments.

Figures (7)

• Figure 1: DM and stellar surface mass density maps of the GRT cluster. The upper left and right panels show DM structures inside the virial radius ($R_{\rm{vir}}$) of the GRT cluster at $z=0$ in the base simulation and the GRT simulation, respectively. The lower left and right panels show the stellar structures in $R_{\rm{vir}}$ and 0.5$R_{\rm{vir}}$ of the GRT cluster. The color scale for DM and stellar structures is shown to the right of the panels. For reference, the stellar surface mass density range shown in the colorbar corresponds approximately to $\mu_V \sim 23.1-33.1~\rm{mag}~\rm{arcsec}^{-2}$ assuming a $V$-band mass-to-light ratio $(M_\star/L_V)$ of $5~M_\odot/L_{\odot,V}$. Figure credit from chun2022.
• Figure 2: Mass growth history of the GRT cluster. The thick gray and thin black solid lines represent the growth history of the cluster in the base simulation and the GRT simulation, respectively. The dash-dotted line indicates the mass growth of the stars in the GRT cluster. The black arrow below the x-axis means the epoch of the last major merger of the cluster. Figure credit from chun2022.
• Figure 3: Left: the relation between $M_{\rm{200c}}$ and $z_{\rm{m50}}$ of GRT clusters at $z=0$. The filled red and blue circles indicate the relaxed and unrelaxed clusters. The horizontal dashed gray line is the median $z_{\rm{m50}}$ of all clusters in the $N$-cluster run within a logarithmic mass bin of 0.25 dex. Right: the relation between $M_{\rm{200c}}$ and ICL fraction ($f_{\rm{ICL}}$) within $r_{\rm{200c}}$ of GRT clusters at $z=0$. The filled red and blue circles indicate the median $f_{\rm{ICL}} (< r_{\rm{200c}})$ among the ICL fractions calculated on the three different planes for relaxed and unrelaxed clusters. The error bar caps are the upper and lower values of the ICL fractions for each cluster. Figure adapted from chun2024.
• Figure 4: Top: The contribution to the total ICL luminosity within the relaxed and unrelaxed GRT clusters depending on the mass of the satellites. The filled red, blue, and green circles indicate the subgroups called the "group mass,’’ "intermediate mass,’’ and "low mass’’ satellites, and each error bar cap means the first and third quartiles for each subgroup. Bottom: The relation between the mass of clusters and the contribution of satellites to the ICL within the clusters, categorized depending on the three different formation mechanisms. The open circles, filled squares, and filled diamonds indicate the contribution of disrupted ICL, stripped ICL, and preprocessed ICL to the total ICL stars. Figure adapted from chun2024.
• Figure 5: $V$-band surface brightness ($\mu_V$) map of the most massive GRT cluster at $z=0$. Color bars indicate the $V$-band surface brightness. The zoomed-in images on the right side show the stellar distribution diagram of the representative tidal tail, stream, and shell-like structures. Figure adapted from chun2026.