The Stellar Mass Function for Nine Massive Galaxy Clusters in the Local Universe

Abstract

We measure galaxy stellar mass functions (SMFs) for nine of the most massive galaxy clusters in the local universe ($0.07 < z < 0.11$) using deep and complete spectroscopy from the MAssive Cluster Survey with Hectospec (MACH). We construct the cluster SMFs down to $\log(M_*/M_\odot) \gtrsim 8.5$. For comparison, we measure the SMF for field galaxies, complete to $\log(M_*/M_\odot) \gtrsim 10.5$, based on Sloan Digital Sky Survey (SDSS) spectroscopy over the same redshift range. The mean MACH SMF shows a shape similar to that of the field SMF but with a significantly higher amplitude at $\log(M_*/M_\odot) < 11.4$. At $\log(M_*/M_\odot) > 11.4$, the MACH SMF shows a clear excess, indicating the contribution of massive galaxies, including Brightest Cluster Galaxies (BCGs). Based on homogeneous MACH spectroscopy, we compare SMF shapes for quiescent and star-forming members as a function of cluster-centric distance. The quiescent SMFs display a curved shape with a peak at $\log(M_*/M_\odot) \approx 10.5$; the star-forming SMFs decline monotonically with increasing stellar mass. We further compare the mean MACH SMF with SMFs derived from similarly massive clusters in the IllustrisTNG-300 simulations. The shape of the observed and simulated SMFs agree well overall. However, the MACH clusters contain roughly a factor of two more galaxies at $9.0 < \log(M_*/M_\odot) < 10.5$. These results demonstrate that constructing cluster SMFs from complete spectroscopic samples can test simulations and provide powerful constraints on galaxy formation and evolution in dense environments.

Figures (22)

• Figure 1: $M_{200}$ of galaxy clusters in the HeCS-omnibus sample Sohn2020 as a function of the number of galaxies with spectroscopy within each cluster field. Stars and circles indicate the MACH clusters (this study) and other clusters in the HeCS-omnibus sample Sohn2020, respectively. Redder symbols indicate clusters at higher redshifts. The size of the symbol is proportional to the number of spectroscopically identified cluster members within $R_{200}$.
• Figure 2: Spectroscopic survey completeness for galaxies within each cluster field (i.e., $R_\mathrm{cl} < R_{200}$), as a function of the foreground extinction-corrected $r$-band composite model magnitude. The black vertical dotted lines indicate a cumulative completeness of 90% for each cluster. The $M_{200}$ of the clusters increases from left to right and from top to bottom.
• Figure 3: Spectroscopic survey completeness map for galaxies with $r_{\mathrm{cModel,0}} < 20.5$ in the MACH cluster fields. Darker colors indicate higher completeness. White points are spectroscopically identified cluster members. White contours show the projected number density of cluster members. Red and yellow dashed circles mark $R_{500}$ and $R_{200}$, respectively.
• Figure 4: The Dynamical Properties of MACH clusters and Cluster Membership
• Figure 5: The R--v diagram for galaxies in the MACH cluster fields. Gray circles indicate galaxies with spectroscopic redshifts. Blue circles show member galaxies identified based on the caustic technique: black solid lines show the caustic boundaries. Red and orange vertical lines mark $R_{500}$ and $R_{200}$, respectively.