The RAWS Project

SDSS map of the Universe. Credit: Sloan Digital Sky Survey (SDSS)

Background and Motivation

Cosmic filaments are the largest structures in the Universe, forming a vast cosmic web that connects galaxies and clusters across billions of light-years. These filaments are thought to play a crucial role in galaxy formation and evolution, as they funnel gas and dark matter into galaxies, fueling star formation and black hole growth. However, these hypotheses are mainly based on simulations, and observational evidence of the impact of filaments on galaxy properties is still limited.

Methodology

In this project, we introduce the RAWS sample, a comprehensive cross-matched multi-wavelength dataset of galaxies from the following surveys:

Rapid ASKAP Continuum Survey (RACS) for radio data (McConnell et al., 2020)
Wide-field Infrared Survey Explorer (WISE) for infrared data (Wright et al., 2010)
SuperCOSMOS All-Sky Galaxy Survey (SCOS) for optical data (Peacock et al., 2016)

To identify which galaxies in our sample are located within cosmic filaments, we use the filament reconstruction from the Sloan Digital Sky Survey (SDSS) (Carrón Duque et al., 2022).

Key Findings

RAWS I: A clear suppression in the radio source counts of filament galaxies is observed, consistent with the hypothesis that filaments can quench galaxies in intermediate density environments (Hassan et al., 2025)

Radio source counts of filament and non-filament galaxies in the RAWS sample

References

The Rapid ASKAP Continuum Survey I: Design and first results
D. McConnell, C. L. Hale, E. Lenc, J. K. Banfield, George Heald, ...

Publications of the Astronomical Society of Australia, 37, 2020

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The Wide-field Infrared Survey Explorer (WISE) mission description and initial on-orbit performance
Edward L. Wright, Peter R. M. Eisenhardt, Amy K. Mainzer, Michael E. Ressler, Roc M. Cutri, ...

The Astronomical Journal, 140(6), Nov 2010

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The SuperCOSMOS all-sky galaxy catalogue
J. A. Peacock, N. C. Hambly, M. Bilicki, H. T. MacGillivray, L. Miller, ...

Monthly Notices of the Royal Astronomical Society, 462(2), Jul 2016

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A novel cosmic filament catalogue from SDSS data
Javier Carrón Duque, Marina Migliaccio, Domenico Marinucci, and Nicola Vittorio

Astronomy & Astrophysics, 659, Mar 2022

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The RAWS Project: I. Do AGN quench their activity in cosmic filaments at redshifts up to $z \sim 0.6$?
Mohd Shaiful Rizal Hassan, Zamri Zainal Abidin, and Affan Adly Nazri

Monthly Notices of the Royal Astronomical Society, 541(4), Jul 2025

Abstract BibTeX Google HTML PDF

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 ($887.5~\mathrm{MHz}$) and RACS-mid ($1367.5~\mathrm{MHz}$), respectively. Each sample was subdivided into (1) all RAWS galaxies, (2) RAWS filament galaxies, and (3) RAWS non-filament galaxies. We constructed normalized Euclidean $1.4\mathrm{-GHz}$ 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.
```
@article{Hassan2025,
  title = {The {RAWS} {Project}: {I}. {Do} {AGN} quench their activity in cosmic filaments at redshifts up to $z \sim 0.6$?},
  volume = {541},
  issn = {1365-2966},
  url = {http://dx.doi.org/10.1093/mnras/staf1209},
  doi = {10.1093/mnras/staf1209},
  number = {4},
  journal = {Monthly Notices of the Royal Astronomical Society},
  publisher = {Oxford University Press (OUP)},
  author = {Hassan, Mohd Shaiful Rizal and Abidin, Zamri Zainal and Nazri, Affan Adly},
  year = {2025},
  month = jul,
  pages = {3696--3708},
}
```