Pixel Color–Magnitude Diagram Analysis of the Brightest Cluster Galaxies in Dynamically Young and Old Clusters Abell 1139 and Abell 2589

Abstract

As a case study to understand the coevolution of Brightest Cluster Galaxies (BCGs) and their host clusters, we investigate the BCGs in dynamically young and old clusters, Abell 1139 (A1139) and Abell 2589 (A2589). We analyze the pixel color-magnitude diagrams (pCMDs) using deep g-and r-band images, obtained from the Canada-France-Hawaii Telescope observations. After masking foreground/background objects and smoothing pixels in consideration of the observational seeing size, detailed pCMD features are compared between the two BCGs. (1) While the overall shapes of the pCMDs are similar to those of typical early-type galaxies, the A2589-BCG tends to have redder mean pixel color and smaller pixel color deviation at given surface brightness than the A1139-BCG. (2) The mean pixel color distribution as a function of pixel surface brightness (pCMD backbone) indicates that the A2589-BCG formed a larger central body (∼ 2.0 kpc in radius) by major dry mergers at an early epoch than the A1139-BCG (a central body ∼ 1.3 kpc in radius), while they have grown commonly by subsequent minor mergers. (3) The spatial distributions of the pCMD outliers reveal that the A1139-BCG experienced considerable tidal events more recently than the A2589-BCG, whereas the A2589-BCG has an asymmetric compact core possibly resulting from major dry merger at an early epoch. (4) The A2589-BCG shows a very large faint-to-bright pixel number ratio compared to early-type non-BCGs, whereas the ratio for the A1139-BCG is not distinctively large. These results are consistent with the idea that the BCG in the dynamically older cluster (A2589) formed earlier and is relaxed better.

Color Dispersion as an Indicator of Stellar Population Complexity: Insights from the Pixel Color–Magnitude Diagrams of 32 Bright Galaxies in Abell 1139 and Abell 2589

“…A candidate for such a simple and efficient methodology to trace the formation history of a galaxy is the pixel color-magnitude diagram (pCMD) analysis (Bothun 1986;Abraham et al 1999;de Grijs et al 2003;Lanyon-Foster et al 2007;Lee et al 2011Lee et al , 2012Lee et al , 2017. This method has not been very widely used until now, but it has potential to be a powerful approach to total understanding of the photometric and structural properties of galaxies.…”

“…For example, Lanyon-Foster et al (2007) showed that galaxies in variety of morphological types show various and distinct features in their pCMDs, such as prime sequences for early-type galaxies and inverse-L features for spiral galaxies. Compared to the classical photometric and/or structural analysis methods, the pCMD analysis has several advantages: (1) it can be consistently applied to galaxies with any kind of morphology, (2) it considers the photometric and structural properties at the same time, and (3) it is efficient in checking the homology between galaxies in different mass or size scales (Lee et al 2017).…”

“…Despite such merits, however, the usage of the pCMD analysis is not perfectly established yet. As an effort to devise a quantitative analysis method using pCMDs, Lee et al (2017) introduced simple routines to compare pCMDs to check the similarity in galaxy formation history. They compared the brightest cluster galaxies (BCGs) in Abell 1139 (A1139) and Abell 2589 (A2589) using the pCMD analysis technique, which are two of the 14 galaxy clusters targeted in the KASI-Yonsei Deep Imaging Survey of Clusters (KYDISC; Oh et al 2018).…”

“…They compared the brightest cluster galaxies (BCGs) in Abell 1139 (A1139) and Abell 2589 (A2589) using the pCMD analysis technique, which are two of the 14 galaxy clusters targeted in the KASI-Yonsei Deep Imaging Survey of Clusters (KYDISC; Oh et al 2018). By simplifying the overall pCMD features into the mean and standard deviation of pixel color as a function of pixel surface brightness (called a pCMD backbone), Lee et al (2017) showed that the BCG of dynamically relaxed A2589 formed a larger central body at an early epoch and has grown to be a larger, more massive and dynamically better relaxed galaxy today than the BCG of dynamically young A1139. Those results support the idea that a BCG and its host cluster coevolve.…”

Detailed Studies of Lencitular Galaxies in the Local Universe

“…To understand the stellar population of the galaxy' components, we used newly developed pixelized color-magnitude diagrams. This type of diagram was previously studied in Cook et al (2019); Lee et al (2018Lee et al ( , 2017; Conroy and van Dokkum (2016) and present a new way to understand the stellar populations of galaxies using the magnitudes and colors of each pixel of the models at the different wavelengths. For this work, we have studied the pixelized color-magnitude diagram using the NUV-r colour.…”