Probing the magnetized gas distribution in galaxy groups and the cosmic web with POSSUM Faraday rotation measures

ABSTRACT We present initial results from the Polarization Sky Survey of the Universe’s Magnetism (POSSUM), analysing 22 817 Faraday rotation measures (RMs) with median uncertainties of 1.2 rad m$^{-2}$ across 1520 deg2 to study magnetized gas associated with 55 nearby galaxy groups ($z\lesssim 0.025$) with halo masses between $10^{12.5}$ and $10^{14.0}$ M$_\odot$. We identify two distinct gas phases: the intragroup medium (IGrM) within 0–2 splashback radii and the warm-hot intergalactic medium (WHIM) extending from 2 to 7 splashback radii. These phases enhance the standard deviation of residual (i.e. Galactic foreground RM-subtracted) RMs by $6.9\pm 1.8$ rad m$^{-2}$ and $4.2 \pm 1.2$ rad m$^{-2}$, respectively. Estimated magnetic field strengths are several μG within the IGrM and 0.1–1 μG in the WHIM. We estimate the plasma $\beta$ in both phases, and show that magnetic pressure might be more dynamically important than in the ICM of more massive clusters or sparse cosmic web filaments. Our findings indicate that ‘missing baryons’ in the WHIM likely extend beyond the gravitational radii of group-mass haloes to Mpc scales, consistent with large-scale, outflow-driven ‘magnetized bubbles’ seen in cosmological simulations. We demonstrate that RM grids are an effective method for detecting magnetized thermal gas at galaxy group interfaces and within the cosmic web. This approach complements X-ray and Sunyaev-Zel’dovich effect methods, and when combined with fast radio burst dispersion measures, data from the full POSSUM survey – comprising approximately a million RMs – will allow direct magnetic field measurements to further our understanding of baryon circulation in these environments and the magnetized universe.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2024-08-30
DOI
https://doi.org/10.1093/mnras/stae1954
Citations
10
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
3.32

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article

Probing the magnetized gas distribution in galaxy groups and the cosmic web with POSSUM Faraday rotation measures

E. Osinga, Yik Ki, N. M. McClure‐Griffiths, Simon Duchesne et al.
10 citations
Monthly Notices of the Royal Astronomical Society
Galaxies: Formation, Evolution, Phenomena
3.32
article

Probing the magnetized gas distribution in galaxy groups and the cosmic web with POSSUM Faraday rotation measures

E. Osinga, Yik Ki, N. M. McClure‐Griffiths, Simon Duchesne, Jane Kaczmarek, Takuya Akahori, A. J. M. Thomson, G. Heald, S. M. Bradbury, L. Rudnick, B. M. Gaensler, E. Carretti, C. Stuardi, C. S. Anderson, S. P. O’Sullivan, Jennifer West, Leonard Baidoo, Tessa Vernstrom, D. A. Leahy, F. Loi, Amit Seta, S Lyla Jung, M. Brüggen
article en
10 citations

Abstract

ABSTRACT We present initial results from the Polarization Sky Survey of the Universe’s Magnetism (POSSUM), analysing 22 817 Faraday rotation measures (RMs) with median uncertainties of 1.2 rad m$^{-2}$ across 1520 deg2 to study magnetized gas associated with 55 nearby galaxy groups ($z\lesssim 0.025$) with halo masses between $10^{12.5}$ and $10^{14.0}$ M$_\odot$. We identify two distinct gas phases: the intragroup medium (IGrM) within 0–2 splashback radii and the warm-hot intergalactic medium (WHIM) extending from 2 to 7 splashback radii. These phases enhance the standard deviation of residual (i.e. Galactic foreground RM-subtracted) RMs by $6.9\pm 1.8$ rad m$^{-2}$ and $4.2 \pm 1.2$ rad m$^{-2}$, respectively. Estimated magnetic field strengths are several μG within the IGrM and 0.1–1 μG in the WHIM. We estimate the plasma $\beta$ in both phases, and show that magnetic pressure might be more dynamically important than in the ICM of more massive clusters or sparse cosmic web filaments. Our findings indicate that ‘missing baryons’ in the WHIM likely extend beyond the gravitational radii of group-mass haloes to Mpc scales, consistent with large-scale, outflow-driven ‘magnetized bubbles’ seen in cosmological simulations. We demonstrate that RM grids are an effective method for detecting magnetized thermal gas at galaxy group interfaces and within the cosmic web. This approach complements X-ray and Sunyaev-Zel’dovich effect methods, and when combined with fast radio burst dispersion measures, data from the full POSSUM survey – comprising approximately a million RMs – will allow direct magnetic field measurements to further our understanding of baryon circulation in these environments and the magnetized universe.

Monthly Notices of the Royal Astronomical SocietyVol. 533(4)
Australian National University (AU), Universidad Complutense de Madrid (ES), Commonwealth Scientific and Industrial Research Organisation (AU), University of Minnesota (US), Universität Hamburg (DE), University of Calgary (CA), The University of Western Australia (AU), University of California, Santa Cruz (US), University of Toronto (CA), Dominion Astrophysical Observatory (CA), University of Oxford (GB), Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna (IT), Canadian Institute for Theoretical Astrophysics (CA), Astronomy and Space (AU), National Astronomical Observatory of Japan (JP), International Centre for Radio Astronomy Research (AU), National Institute for Astrophysics (IT)
Science and Industry Endowment Fund, Comunidad de Madrid, Commonwealth Scientific and Industrial Research Organisation, Canada Research Chairs, University of Toronto, Natural Sciences and Engineering Research Council of Canada, Japan Society for the Promotion of Science
Openalex Percentile: Top 8%
Galaxies: Formation, Evolution, Phenomena
3.32
DOIOpen Access PDFOpenAlex
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