Galaxy And Mass Assembly (GAMA): The galaxy luminosity function within the cosmic web

TL;DR

This study examines how the galaxy luminosity function varies across different cosmic web environments using GAMA survey data, finding apparent differences driven by local density rather than direct web influence.

Contribution

It introduces a tidal tensor-based classification of the cosmic web and demonstrates that observed luminosity function variations are due to local density effects, not direct web influence.

Findings

Luminosity function normalization varies significantly across environments.

Turnover magnitude brightens from voids to knots.

Differences are explained by local density, not direct web effects.

Abstract

We investigate the dependence of the galaxy luminosity function on geometric environment within the Galaxy And Mass Assembly (GAMA) survey. The tidal tensor prescription, based on the Hessian of the pseudo-gravitational potential, is used to classify the cosmic web and define the geometric environments: for a given smoothing scale, we classify every position of the surveyed region, $0.04<{z}<0.26$, as either a void, a sheet, a filament or a knot. We consider how to choose appropriate thresholds in the eigenvalues of the Hessian in order to partition the galaxies approximately evenly between environments. We find a significant variation in the luminosity function of galaxies between different geometric environments; the normalisation, characterised by $\phi^{*}$ in a Schechter function fit, increases by an order of magnitude from voids to knots. The turnover magnitude, characterised by $M^*$, brightens by approximately $0.5$ mag from voids to knots. However, we show that the observed modulation can be entirely attributed to the indirect local-density dependence. We therefore find no evidence of a direct influence of the cosmic web on the galaxy luminosity function.