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

Anderson, Craig S.; Heald, G.; Eilek, J. A.; Lenc, E.; Gaensler, B. M.; Rudnick, Lawrence; Eck, Cameron L. Van; O’Sullivan, S. P.; Stil, J. M.; Chippendale, A. P.; Riseley, C. J.; Carretti, E.; West, Jennifer L.; Farnes, J. S.; Harvey-Smith, Lisa; McClure-Griffiths, N. M.; Bock, Douglas C.-J.; Bunton, John D.; Koribalski, B. S.; Tremblay, Chenoa D.; Voronkov, M. A.; Warhurst, K.

doi:10.1017/pasa.2021.4

Cited by 31 publications

(25 citation statements)

References 137 publications

(208 reference statements)

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“…GASKAP is unique amongst the ASKAP surveys in its requirement for high spectral resolution. The standard ASKAP spectral resolution is ν = 1 MHz for the continuum surveys (EMU; Norris et al 2011;POSSUM Murphy et al 2013;VAST;Anderson et al 2021) and ν = 18.5 kHz, optimised for extragalactic HI surveys like WALLABY (Koribalski et al 2020), DINGO (Meyer et al 2017), andFLASH (Allison et al 2020). By contrast, GASKAP is designed to fully resolve the spectral linewidths observed in cold HI, OH masers, and OH absorption, requiring frequency resolution of ν 5 kHz.…”

Section: Askap Observations and The Gaskap-hi Pilot Surveymentioning

confidence: 99%

GASKAP-HI pilot survey science I: ASKAP zoom observations of Hi emission in the Small Magellanic Cloud

Pingel

Dempsey

McClure‐Griffiths

et al. 2022

Publ. Astron. Soc. Aust.

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We present the most sensitive and detailed view of the neutral hydrogen ( ${\rm H\small I}$ ) emission associated with the Small Magellanic Cloud (SMC), through the combination of data from the Australian Square Kilometre Array Pathfinder (ASKAP) and Parkes (Murriyang), as part of the Galactic Australian Square Kilometre Array Pathfinder (GASKAP) pilot survey. These GASKAP-HI pilot observations, for the first time, reveal ${\rm H\small I}$ in the SMC on similar physical scales as other important tracers of the interstellar medium, such as molecular gas and dust. The resultant image cube possesses an rms noise level of 1.1 K ( $1.6\,\mathrm{mJy\ beam}^{-1}$ ) $\mathrm{per}\ 0.98\,\mathrm{km\ s}^{-1}$ spectral channel with an angular resolution of $30^{\prime\prime}$ ( ${\sim}10\,\mathrm{pc}$ ). We discuss the calibration scheme and the custom imaging pipeline that utilises a joint deconvolution approach, efficiently distributed across a computing cluster, to accurately recover the emission extending across the entire ${\sim}25\,\mathrm{deg}^2$ field-of-view. We provide an overview of the data products and characterise several aspects including the noise properties as a function of angular resolution and the represented spatial scales by deriving the global transfer function over the full spectral range. A preliminary spatial power spectrum analysis on individual spectral channels reveals that the power law nature of the density distribution extends down to scales of 10 pc. We highlight the scientific potential of these data by comparing the properties of an outflowing high-velocity cloud with previous ASKAP+Parkes ${\rm H\small I}$ test observations.

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Section: Askap Observations and The Gaskap-hi Pilot Surveymentioning

confidence: 99%

GASKAP-HI pilot survey science I: ASKAP zoom observations of Hi emission in the Small Magellanic Cloud

Pingel

Dempsey

McClure‐Griffiths

et al. 2022

Publ. Astron. Soc. Aust.

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“…The data analyzed in this work consists of the H i image obtained with MeerKAT and already published by Kleiner et al (2021), together with the polarized image and RM image obtained with ASKAP during commissioning tests of the telescope in view of the Early Science program which covered the Fornax cluster (Anderson et al 2021). The commissioning observations presented here correspond to a different scheduling block with respect to the Fornax cluster observations by Anderson et al (2021). As we describe in the following, the settings are not the same.…”

Section: Datamentioning

confidence: 99%

A depolarizing HI tidal tail in the western lobe of Fornax A

Loi,

Serra,

Murgia

et al. 2022

Preprint

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Recent MeerKAT neutral hydrogen (H i) observations of Fornax A reveal tidal material intersecting in projection the western lobe of this radio galaxy. We found a spatial coincidence between the northern H i tail and a depolarized structure observed for the first time with the Australian Square Kilometre Array Pathfinder (ASKAP) at 1.2 GHz. We analyzed the properties of the rotation measure (RM) image obtained with ASKAP data at the location of the H i tail and in its neighborhood. We modeled the observed RM structure function to investigate the magnetic field power spectrum at the location of the H i tail and in a nearby control region. We found that the observed RM, in the control region and in a region enclosing the H i tail, cannot be due to the intracluster Faraday screen caused by the Fornax cluster. An intragroup magnetized medium with a central magnetic field strength of 18.5 µG can explain the control region RM, but it is clear that there is an excess in correspondence with the H i tail region. We evaluated several scenarios in which the H i tail is either in the lobe foreground or embedded in the lobe. We determined a magnetic field strength on the order of ∼9.5−11 µG in the H i tail, a value consistent with constraints derived from narrowband Hα imaging of the ionized gas. The spatial coincidence between H i tail and depolarization analyzed in this paper could be the first observed evidence of a magnetic field that either has passed through a radio galaxy lobe or has survived the lobe expansion.

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“…The ICM is weakly magnetized, with plasma beta ∼ 100 (𝛽 = 8𝜋𝑃/B• B) (Carilli & Taylor 2002;Govoni & Feretti 2004;Bonafede et al 2010;Anderson et al 2021). From Alfvèn's flux freezing theorem, the field lines are frozen into the plasma and have to move along with it.…”

Section: Effect Of Magnetic Fieldsmentioning

confidence: 99%

Characterising the turbulent multiphase halos with periodic box simulations

Mohapatra,

Jetti,

Sharma

et al. 2021

Preprint

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Turbulence in the intracluster medium (ICM) is driven by active galactic nuclei (AGNs) jets, by mergers, and in the wakes of infalling galaxies. It not only governs gas motion but also plays a key role in the ICM thermodynamics. Turbulence can help seed thermal instability by generating density fluctuations, and mix the hot and cold phases together to produce intermediate temperature gas (10 4 -10 7 K) with short cooling times. We conduct high resolution (384 3 -768 3 resolution elements) idealised simulations of the multiphase ICM and study the effects of turbulence strength, characterised by 𝑓 turb (0.001-1.0), the ratio of turbulent forcing power to the net radiative cooling rate. We analyse density and temperature distribution, amplitude and nature of gas perturbations, and probability of transitions across the temperature phases. We also study the effects of mass and volume weighted thermal heating and weak ICM magnetic fields. For low 𝑓 turb , the gas is distribution is bimodal between the hot and cold phases. The mixing between different phases becomes more efficient with increasing 𝑓 turb , producing larger amounts of the intermediate temperature gas. Strong turbulence ( 𝑓 turb ≥ 0.5) generates larger density fluctuations and faster cooling, and ultimately supersonic gas motions. The rms logarithmic pressure fluctuation scaling with Mach number 𝜎 2 ln P ≈ ln 1 + 𝑏 2 𝛾 2 M 4 is unaffected by thermal instability and is the same as in hydro turbulence. In contrast, the density fluctuations characterised by 𝜎 2 𝑠 are much larger, especially for M 0.5. In magnetohydrodynamic runs, magnetic fields provide significant pressure support in the cold phase but do not have any strong effects on the diffuse gas distribution, and nature and amplitude of fluctuations.

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

Cited by 31 publications

References 137 publications

GASKAP-HI pilot survey science I: ASKAP zoom observations of Hi emission in the Small Magellanic Cloud

GASKAP-HI pilot survey science I: ASKAP zoom observations of Hi emission in the Small Magellanic Cloud

A depolarizing HI tidal tail in the western lobe of Fornax A

Characterising the turbulent multiphase halos with periodic box simulations

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