2025MNRAS.541.3696H

The role of cosmic filaments in galaxy evolution remains uncertain, with conflicting evidence for both enhancement and suppression of star formation (SF) and active galactic nucleus (AGN) activity. In this first paper of the RAWS (RACS-WISE-SCOS-SDSS) project, we investigate the radio properties of galaxies in filaments by analysing source counts of radio sources from the Rapid ASKAP Continuum Survey (RACS), cross-matched with data from the Wide-field Infrared Survey Explorer (WISE), SuperCOSMOS Sky Survey (SCOS), and Sloan Digital Sky Survey (SDSS) filament reconstructions. Two samples - RAWS-low and RAWS-mid - were derived from RACS-low (887.5 MHz) and RACS-mid (1367.5 MHz), respectively. Each sample was subdivided into (1) all RAWS galaxies, (2) RAWS filament galaxies, and (3) RAWS non-filament galaxies. We constructed normalized Euclidean 1.4-GHz source counts for all subsamples. The results show that AGNs dominate all samples. The source counts for subsamples (1) and (3) agree well with those from previous radio surveys. However, we observe a clear suppression in the source counts of filament galaxies (subsample 2) across both RACS frequencies. This suggests a lower surface density of AGN in filamentary environments compared to field galaxies, possibly due to environmental processes such as ram-pressure stripping, gas depletion, or intergalactic medium (IGM) interactions. These findings are consistent with simulations predicting gradual quenching in intermediate-density environments. While our results support the idea that filaments may suppress AGN activity up to $z\sim 0.6$, further investigation is needed to understand their dual role in both quenching and fuelling galaxy evolution.