Dissecting the Perseus-Pisces supercluster observed with CFHT-MegaCam: Investigating environmental effects on galaxy morphology

TL;DR

This study probes environmental effects on galaxy morphology within the nearby Perseus–Pisces filament by combining deep CFHT–MegaCam imaging with a robust 3D filament skeleton derived via DisPerSE. By constructing a large spectroscopic catalogue, applying FoG corrections, and classifying galaxies into cluster, group, filament, and outskirts contexts, the authors quantify morphology and interaction trends as a function of distance to filaments and dense nodes. They reveal clear morphological and stellar-mass segregation, with early-type systems concentrated in dense nodes and along filament spines, and late-type systems more prevalent in filaments and outskirts; they also detect enhanced local interactions in filaments and groups. The results provide empirical benchmarks for how large-scale structure drives pre-processing and environmental quenching, informing models of galaxy evolution in the cosmic web and aiding interpretation of high-redshift observations in the era of Euclid and LSST.

Abstract

The discovery of the large-scale structure has transformed our view of galaxy formation and evolution. Filaments of the cosmic web provide key environments that channel the growth of structures. Guided by predictions from cosmological simulations, we study the morphological distribution of galaxies in the Perseus-Pisces Supercluster, a prominent filamentary complex at 70 Mpc. We focus on how galaxy morphology and structural disturbances relate to position within the filament network and to proximity to dense nodes. Our sample is built from a spectroscopic catalogue cross-matched with deep r-band CFHT/MegaCam imaging from UNIONS and additional time, enabling the detection of low-surface-brightness features and extended outer structures. Morphologies are determined both visually and through structural parameters extracted from surface-brightness profiles using AutoProf and AstroPhot. The 3D filamentary skeleton of Perseus-Pisces is reconstructed with the DisPerSE algorithm, providing distances from each galaxy to the nearest filament and to group or cluster centres. The 3D mapping reveals a network of interconnected sub-filaments converging around the Pisces cluster, forming a complex, multi-branched structure that likely shapes environmental effects on galaxy evolution. We observe clear morphological and stellar-mass segregation: massive early-type galaxies (E/S0) concentrate along filament spines and near dense nodes, while late-type and irregular systems are more broadly dispersed. About 10-13% of galaxies show strong signs of gravitational interaction, with stellar-halo asymmetries particularly common in filaments and groups. These findings underline the dual influence of filamentary environments, which both host evolved early-type systems and foster local tidal interactions and pre-processing that modify galaxy morphology.

Figures (26)

• Figure 1: Observation tile in the CFHT/Megacam $r$-band band covering a region of 1.2 deg$^2$ near the Perseus cluster (visible in the lower left corner of the image), optimized for low surface brightness detection (3×3 binning).
• Figure 2: Sky-projected distribution of galaxies in the PPSC catalog. Grey dots represent galaxies from the PPSC catalog. Group and cluster centres identified are shown as gold points: from the left to the right in the region A, A 426, AWM7, a group with UGC 1841, and A 347. The projected skeleton, extracted from our final 3D structure, is represented by dark lines and traces the projected filamentary network. The boundaries of the region A and the region B are shown in purple and blue, respectively. A cyan contour indicates the footprint of the Euclid ERO Perseus field, overlaid for reference.
• Figure 3: Three-dimensional reconstruction of the PPSC. Grey dots represent galaxies from the PPSC catalog, pink dots correspond to galaxies in the region A, and blue dots indicate galaxies in the region B. The final filamentary skeleton, shown as dark lines, is extracted using DisPerSE from a filament density grid built from multiple realizations of the galaxy distribution. The red arrows mark the cone of interest and highlight the directions of increasing redshift.
• Figure 4: Example of AutoProf processing for an isolated galaxy, UGC 0742, in the region B. Left: masked image with segmentation overlaid. Middle: 2D isophotal extraction. Right: radial surface brightness profile with Sérsic fit out to $R_{25}$. The profiles reach $\sim$29--30 mag arcsec$^{-2}$, which is representative of the depth achieved for the majority of galaxies in our dataset.
• Figure 5: Example of AstroPhot modelling in a crowded region. Sérsic profiles are fitted to individual galaxies from the PPSC catalog, displayed on this $2000 \times 2000$ pixel tile.