The POlarised GLEAM Survey (POGS) II: Results from an all-sky rotation measure synthesis survey at long wavelengths

Riseley, C. J.; Galvin, Tim J.; Sobey, C.; Vernstrom, Tessa; White, Sarah V.; Zhang, X.; Gaensler, B. M.; Heald, G.; Anderson, Craig S.; Franzen, T. M. O.; Hancock, P. J.; Hurley‐Walker, N.; Lenc, E.; Eck, Cameron L. Van

doi:10.1017/pasa.2020.20

Cited by 35 publications

(28 citation statements)

References 124 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These results demonstrate that deep, wide-field RM grid studies have the capacity to reveal the gas in and around galaxy clusters in a diverse set of regimes. This being the case, impending deep all-sky linear polarisation surveys like POSSUM, the VLA Sky Survey (VLASS; Lacy et al 2019), the POlarised GLEAM survey (POGS; Riseley et al 2018;Riseley et al 2020), and the LOFAR Two-Metre Sky Survey (LoTSS; Shimwell et al 2017) will all help to revolutionise our understanding of large samples of such objects, while much deeper targeted observations like the MeerKAT Fornax Survey (Serra et al 2016) will reveal a wealth of structure in individual clusters that has gone heretofore unseen.…”

Section: Resultsmentioning

confidence: 99%

Early Science from POSSUM: Shocks, turbulence, and a massive new reservoir of ionised gas in the Fornax cluster

Anderson

Heald

Eilek

et al. 2021

Publ. Astron. Soc. Aust.

Self Cite

View full text Add to dashboard Cite

We present the first Faraday rotation measure (RM) grid study of an individual low-mass cluster—the Fornax cluster—which is presently undergoing a series of mergers. Exploiting commissioning data for the POlarisation Sky Survey of the Universe’s Magnetism (POSSUM) covering a ${\sim}34$ square degree sky area using the Australian Square Kilometre Array Pathfinder (ASKAP), we achieve an RM grid density of ${\sim}25$ RMs per square degree from a 280-MHz band centred at 887 MHz, which is similar to expectations for forthcoming GHz-frequency ${\sim}3\pi$ -steradian sky surveys. These data allow us to probe the extended magnetoionic structure of the cluster and its surroundings in unprecedented detail. We find that the scatter in the Faraday RM of confirmed background sources is increased by $16.8\pm2.4$ rad m−2 within 1 $^\circ$ (360 kpc) projected distance to the cluster centre, which is 2–4 times larger than the spatial extent of the presently detectable X-ray-emitting intracluster medium (ICM). The mass of the Faraday-active plasma is larger than that of the X-ray-emitting ICM and exists in a density regime that broadly matches expectations for moderately dense components of the Warm-Hot Intergalactic Medium. We argue that forthcoming RM grids from both targeted and survey observations may be a singular probe of cosmic plasma in this regime. The morphology of the global Faraday depth enhancement is not uniform and isotropic but rather exhibits the classic morphology of an astrophysical bow shock on the southwest side of the main Fornax cluster, and an extended, swept-back wake on the northeastern side. Our favoured explanation for these phenomena is an ongoing merger between the main cluster and a subcluster to the southwest. The shock’s Mach angle and stand-off distance lead to a self-consistent transonic merger speed with Mach 1.06. The region hosting the Faraday depth enhancement also appears to show a decrement in both total and polarised radio emission compared to the broader field. We evaluate cosmic variance and free-free absorption by a pervasive cold dense gas surrounding NGC 1399 as possible causes but find both explanations unsatisfactory, warranting further observations. Generally, our study illustrates the scientific returns that can be expected from all-sky grids of discrete sources generated by forthcoming all-sky radio surveys.

show abstract

Section: Resultsmentioning

confidence: 99%

Early Science from POSSUM: Shocks, turbulence, and a massive new reservoir of ionised gas in the Fornax cluster

Anderson

Heald

Eilek

et al. 2021

Publ. Astron. Soc. Aust.

Self Cite

View full text Add to dashboard Cite

show abstract

“…In sampling this new low-frequency parameter space, it is crucial to have radio telescopes with the ability to perform wide-area surveys of the sky combined with the required sensitivity to observe large samples of RLAGN -past surveys such as 3CRR (Laing et al 1983) are severely biased towards the most luminous sources such as Fanaroff-Riley type-II objects (FR-II; Fanaroff & Riley 1974). Recently, Riseley et al (2020) presented the POlarised GaLactic and Extragalactic All-Sky MWA Survey-the POlarised GLEAM Survey (POGS) in the frequency range 169-231 MHz at a resolution of 3 arcmin (at the highest), with 484 polarized RLAGN detected in the entire southern sky. However, instruments with the capability to perform sub-arcmin resolution surveys are more ideal in resolving the different components of RLAGN (core and lobes) and also mitigate the effects of beam depolarization in small angular size sources.…”

Section: Low Frequency Polarizationmentioning

confidence: 99%

A low-frequency study of linear polarization in radio galaxies

Mahatma

Hardcastle

Harwood

et al. 2020

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Radio galaxies are linearly polarized – an important property that allows us to infer the properties of the magnetic field of the source and its environment. However, at low frequencies, Faraday rotation substantially depolarizes the emission, meaning that comparatively few polarized radio galaxies are known at low frequencies. Using the LOFAR Two-metre Sky Survey at 150 MHz and at a resolution of 20 arcsec, we select 342 radio galaxies brighter than 50 mJy and larger than 100 arcsec in angular size, of which 67 are polarized (18 per cent detection fraction). These are predominantly Fanaroff–Riley type II sources. The detection fraction increases with total flux density, and exceeds 50 per cent for sources brighter than 1 Jy. We compare the sources in our sample detected by the LOw Frequency ARray (LOFAR) to those also detected in NRAO VLA Sky Survey at 1400 MHz, and find that our selection bias towards bright radio galaxies drives a tendency for sources depolarized between 1400 and 150 MHz to have flatter spectra over that frequency range than those that remain polarized at 150 MHz. By comparing observed rotation measures with an analytic model, we find that we are preferentially sensitive to sources in low-mass environments. We also infer that sources with one polarized hotspot are inclined by a small angle to the line of sight, while sources with hotspots in both lobes lie in the plane of the sky. We conclude that low-frequency polarization in radio galaxies is related to a combination of environment, flux density, and jet orientation.

show abstract

“…In order to gather as much information as possible to discuss the nature of GLEAM J0917-0012 (Section 5), we checked for radio polarisation at ν <10 GHz, where our signal-to-noise ratio is the most suitable to perform this analysis. In linear polarisation, GLEAM J0917-0012 is detected neither in the 169−231 MHz MWA POlarised GLEAM Survey (POGS; 7σ fractional polarisation upper limit ≈ 4.2% for GLEAM J0917-0012; Riseley et al 2020) nor in the 1.4-GHz NRAO VLA Sky Survey (NVSS; 5σ fractional polarisation upper limit ≈ 4.7% for GLEAM J0917-0012; Condon et al 1998). We also investigated the radio polarimetric properties from our 5.5-and 9-GHz ATCA data (D20).…”

Section: Radio Polarimetric Properties At < 10 Ghzmentioning

confidence: 99%

The nature and likely redshift of GLEAM J0917–0012

Drouart

Seymour

Broderick

et al. 2021

Publ. Astron. Soc. Aust.

View full text Add to dashboard Cite

We previously reported a putative detection of a radio galaxy at $z=10.15$ , selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The redshift of this source, GLEAM J0917–0012, was based on three weakly detected molecular emission lines observed with the Atacama Large Millimetre Array (ALMA). In order to confirm this result, we conducted deep spectroscopic follow-up observations with ALMA and the Karl Jansky Very Large Array (VLA). The ALMA observations targeted the same CO lines previously reported in Band 3 (84–115 GHz) and the VLA targeted the CO(4-3) and [CI(1-0)] lines for an independent confirmation in Q-band (41 and 44 GHz). Neither observation detected any emission lines, removing support for our original interpretation. Adding publicly available optical data from the Hyper Suprime-Cam survey, Widefield Infrared Survey Explorer (WISE), and Herschel Space Observatory in the infrared, as well as $<$ 10 GHz polarisation and 162 MHz inter-planetary scintillation observations, we model the physical and observational characteristics of GLEAM J0917–0012 as a function of redshift. Comparing these predictions and observational relations to the data, we are able to constrain its nature and distance. We argue that if GLEAM J0917–0012 is at $z<3,$ then it has an extremely unusual nature, and that the more likely solution is that the source lies above $z=7$ .

show abstract

The POlarised GLEAM Survey (POGS) II: Results from an all-sky rotation measure synthesis survey at long wavelengths

Cited by 35 publications

References 124 publications

Early Science from POSSUM: Shocks, turbulence, and a massive new reservoir of ionised gas in the Fornax cluster

Early Science from POSSUM: Shocks, turbulence, and a massive new reservoir of ionised gas in the Fornax cluster

A low-frequency study of linear polarization in radio galaxies

The nature and likely redshift of GLEAM J0917–0012

Contact Info

Product

Resources

About