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Radio wave scattering by circumgalactic cool gas clumps

Vedantham, H. K. and Phinney, E. S. (2019) Radio wave scattering by circumgalactic cool gas clumps. Monthly Notices of the Royal Astronomical Society, 483 (1). pp. 971-984. ISSN 0035-8711.

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We consider the effects of radio wave scattering by cool ionized clumps (T ∼ 10^4 K) in circumgalactic media (CGMs). The existence of such clumps is inferred from intervening quasar absorption systems, but has long been something of a theoretical mystery. We consider the implications for compact radio sources of the ‘fog-like’ two-phase model of the CGM recently proposed by McCourt et al. In this model, the CGM consists of a diffuse coronal gas (T ≳ 10^6 K) in pressure equilibrium with numerous ≲1 pc scale cool clumps or ‘cloudlets’ formed by shattering in a cooling instability. The areal filling factor of the cloudlets is expected to exceed unity in ≳10^(11.5) M⊙ haloes, and the ensuing radio wave scattering is akin to that caused by turbulence in the Galactic warm ionized medium. If 30 per cent of cosmic baryons are in the CGM, we show that for a cool-gas volume fraction of fv ∼ 10^(−3), sources at z_s ∼ 1 suffer angular broadening by ∼15μ as and temporal broadening by ∼1 ms at λ = 30 cm, due to scattering by the clumps in intervening CGM. The former prediction will be difficult to test (the angular broadening will suppress Galactic scintillation only for <10μ Jy compact synchrotron sources). However the latter prediction, of temporal broadening of localized fast radio bursts, can constrain the size and mass fraction of cool ionized gas clumps as a function of halo mass and redshift, and thus provides a test of the model proposed by McCourt et al.

Item Type:Article
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URLURL TypeDescription Paper
Vedantham, H. K.0000-0002-0872-181X
Additional Information:© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2018 October 13. Received 2018 October 10; in original form 2018 March 7. Published: 26 November 2018. HKV is an R. A. & G. B. Millikan fellow of experimental physics and thanks S. Kulkarni for discussions. ESP’s research was funded in part by the Gordon and Betty Moore Foundation through grant GBMF5076. Figs 1 and 3 were rendered using INKSCAPE and the rest using MATPLOTLIB. Numerical computations were carried out in PYTHON2.7 and employed routines from the NUMPY package.
Group:Astronomy Department
Funding AgencyGrant Number
Robert A. Millikan FellowshipUNSPECIFIED
Gordon and Betty Moore FoundationGBMF5076
Subject Keywords:scattering, galaxies: haloes
Issue or Number:1
Record Number:CaltechAUTHORS:20190205-110429939
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Official Citation:H K Vedantham, E S Phinney; Radio wave scattering by circumgalactic cool gas clumps, Monthly Notices of the Royal Astronomical Society, Volume 483, Issue 1, 11 February 2019, Pages 971–984,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92667
Deposited By: Tony Diaz
Deposited On:05 Feb 2019 19:11
Last Modified:03 Oct 2019 20:46

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