Mechanisms Affecting Galaxies Nearby and Environmental Trends (MAGNET)

Abstract

[ABRIDGED] Galaxy evolution is shaped by internal and external mechanisms that regulate the baryon cycle and star formation activity. We present a theoretical framework based on the GAlaxy Evolution and Assembly (GAEA) semi-analytic model. We extracted portions of simulated volumes that include isolated galaxies, pairs, group, and filament members at z ~ 0, specifically avoiding massive clusters. Galaxies were classified using both intrinsic (halo-based) and observational (2D projected) parameterizations, reconstructing their environmental histories from z = 2 and identifying mergers, tidal interactions, ram pressure stripping (RPS), and starvation. 2D information decreases isolated and group fractions while doubles pairs. More than half of galaxies remain unaffected by the investigated processes since z = 2. Among affected galaxies, mergers dominate at high stellar masses (40-60% at log(M*/Msun) > 10.5). Tidal interactions are less frequent, and their incidence increases with stellar mass. RPS dominates in groups and filaments at intermediate masses (~50%), while starvation ranges from 20 to 30%. The incidence of the different mechanisms depends strongly on both mass and environment, though their imprints on global properties are often subtle. Distinct evolutionary pathways emerge: log(M*/Msun) < 9.5, galaxies in groups and filaments have a faster mass growth than galaxies in the other environments, especially those undergoing starvation, mergers and, to less extent, RPS. Differences are reduced moving to higher masses, where no clear dependence on physical mechanism emerge, even though at these masses a clear star formation suppression is evident in mergers and starved galaxies. This theoretical investigation provides essential context for the recently started multi-wavelength program Mechanisms Affecting Galaxies Nearby and Environmental Trends (MAGNET), which we introduce here.

Figures (32)

• Figure 1: Overview of the MAGNET field. Small points show existing spectroscopically confirmed galaxies at $z<0.04$. Larger circles show the location of the groups falling in the MAGNET footprint, shown in black. The size of the circles is proportional to the group virial radii. Both circles and points are color coded by redshift. Cyan (purple) solid lines indicate the filament network identified by DisPerSE using galaxies in the range $0<z<0.02$ ($0.02<z<0.04$). The only structures shown outside the MAGNET footprint are Centaurus, Hydra and Antlia, three clusters that are located more than 10$^\circ$ away from our field.
• Figure 2: Polar plot showing the redshift and right ascension distribution of the galaxies (shaded small circles) and groups (larger points) within the MAGNET footprint.
• Figure 3: Example of one of the extracted sub volumes (within the dashed rectangle) and the surrounding region. Each panel shows a different projection. Within the sub-box, galaxies belonging to different environments are highlighted: isolated (rusty red), pairs (orange), filaments (steel blue), groups (forest green). This is based on the 2D environmental definition, i.e. mimicking the observational approach, but no significant changes are seen when adopted the other definitions.
• Figure 4: Frequency of galaxies in the different environments, based on the three adopted definitions of environment. Reported fractions are the median value of the 15 realizations, with the black errorbars showing the binomial errors. Small circles represent the results from the individual extracted sub-boxes and colors refer to sub-boxes with different numbers of neighboring groups, as defined in the labels.
• Figure 5: Comparison between the velocity dispersion distribution (left) and the number of members (right) of the MAGNET field (empty histogram) and the pairs and groups identified in GAEA (green) when using the 2D environment definition. For GAEA, median values are reported. Small circles represent the results from the individual extracted sub-boxes and colors refer to sub-boxes with different numbers of neighboring groups, as defined in the labels.