Galaxy transformation across the cosmic web: The influence zone of filaments

TL;DR

This work investigates how cosmic filaments influence galaxy environments by measuring perpendicular and along-filament galaxy overdensity profiles in two nearby redshift slices. By fitting eight analytic density profiles and constructing normalised density profiles to mitigate incompleteness, the authors quantify filament boundaries and widths, finding a central, nearly constant overdensity out to $\sim 1$ Mpc and a transition to background by $\sim 10$ Mpc, with a filament width that grows from $\approx$2.4 Mpc at $z\sim0.075$ to $\approx$5.6 Mpc at $z\sim0.14$. The analysis reveals mild redshift evolution in filament properties and suggests that baryonic physics, not just cosmic expansion, shapes filament envelopes. These results provide constraints on how large-scale structure environments modulate galaxy evolution and underscore the importance of accounting for observational biases when comparing filaments across cosmic time.

Abstract

The matter distribution in the Universe exhibits a rich variety of structures forming the cosmic web. These structures arise from the anisotropic gravitational collapse of primordial density fluctuations and define the pathways along which galaxies flow from voids to high-density clusters. Local density variations within these structures play a fundamental role in driving the environmental evolution of galaxies. To characterise filament boundaries, we analysed galaxy overdensity profiles around filaments in two redshift ranges: $0.05 < z < 0.1$ and $0.1 < z < 0.3$. Perpendicular and parallel profiles were derived by averaging galaxy overdensity as a function of distance. Characteristic scales and central overdensities were then analysed by fitting analytical models, specifically exponential and power-law families. We also introduced normalised density profiles to account for survey incompleteness. The perpendicular overdensity profiles show a nearly constant value in the central regions $D_{fila} < 1$ Mpc, decreasing at distances up to $\approx 10$ Mpc. The mean physical widths (scale radii) at $0.05 < z < 0.1$ and $0.1 < z < 0.3$ are $2.39 \pm 0.69$ and $5.56 \pm 2.29$ Mpc, respectively. This scale difference between redshift ranges is also evident in the normalised profiles. Conversely, profiles along filaments remain constant at distances larger than $\approx 20$ Mpc from the nearest intersection. Our results show that the influence zone of cosmic filaments extends up to $\sim 10$ Mpc from their spines. Furthermore, a mild evolution in structural parameters is observed over the past $\sim 4$ Gyr, suggesting that filaments undergo measurable changes even at relatively low redshifts.

Figures (10)

• Figure 1: Redshift distribution of the galaxies used in this work.
• Figure 2: Galaxy overdensity as a function of radial distance from the filament spine for galaxies at $0.05 < z < 0.1$ (left panel) and $0.1 < z <0.3$ (right panel). Different symbols and colours indicate the overdensity profiles obtained by excluding galaxies within various distances from the nearest filament intersection: $D_{int} > 0$ (grey dots), $D_{int} > 5$ Mpc (blue line), $D_{int} > 10$ Mpc (red line), $D_{int} > 15$ Mpc (yellow line), $D_{int} > 20$ Mpc (green line), $D_{int} > 25$ Mpc (pink line), and $D_{int} > 30$ Mpc (brown line). Uncertainties are calculated as $\sigma/\sqrt{N_{p}}$, where $\sigma$ is the standard deviation and $N_{p}$ is the number of galaxies in each radial bin.
• Figure 3: Galaxy overdensity profile along filaments for galaxies at $0.05 < z < 0.1$ (left panel) and $0.1 < z <0.3$ (right panel). The different symbols represent profiles taking into account galaxies at different distances from the filament spine: $D_{fila} < 1$ Mpc (grey points), $1<D_{fila}<2$ Mpc (blue line), $2<D_{fila}<4$ Mpc (green line), $4<D_{fila}<6$ Mpc (yellow line), $6<D_{fila}<10$ Mpc (brown line), and $D_{fila} > 10$ Mpc (red points). Uncertainties are similar to Fig \ref{['fig:overdens_perp']}.
• Figure 4: Galaxy overdensity as a function of distance to the filament spine (upper panel). The solid lines represent the best fits using a Gaussian (blue), exponential (green), power-law (pink), GNFW (red), Einasto (orange), double power-law (grey), $\beta-$model (purple), and single power-law (turquoise) models. Middle and lower panels: Residuals between the observed data and the fitted models. Colours correspond to the residuals of the different models as in the upper panel. Uncertainties are similar to those shown in Fig. \ref{['fig:overdens_perp']}.
• Figure 5: Galaxy overdensity as a function of distance to the filament spine (upper panel). Grey and red points correspond to galaxies in the redshift ranges $0.05<z<0.1$ and $0.1<z<0.3$, respectively. Middle and lower panels: Residuals between the observed data and the fitted models. Uncertainties, model fits, and residuals colours are similar to those in Fig. \ref{['fig:overdens_perp_fit']}.