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The properties of ‘dark’ ΛCDM haloes in the Local Group.

Benítez-Llambay, A. and Navarro, J.F. and Frenk, C.S. and Sawala, T. and Oman, K. and Fattahi, A. and Schaller, M. and Schaye, J. and Crain, R.A. and Theuns, T. (2017) 'The properties of ‘dark’ ΛCDM haloes in the Local Group.', Monthly notices of the Royal Astronomical Society., 465 (4). pp. 3913-3926.


We examine the baryon content of low-mass Λ cold dark matter (ΛCDM) haloes (108 < M200/M⊙ < 5 × 109) using the APOSTLE cosmological hydrodynamical simulations. Most of these systems are free of stars and have a gaseous content set by the combined effects of cosmic reionization, which imposes a mass-dependent upper limit, and of ram-pressure stripping, which reduces it further in high-density regions. Haloes mainly affected by reionization (RELHICs; REionization-Limited H i Clouds) inhabit preferentially low-density regions and make up a population where the gas is in hydrostatic equilibrium with the dark matter potential and in thermal equilibrium with the ionizing UV background. Their thermodynamic properties are well specified, and their gas density and temperature profiles may be predicted in detail. Gas in RELHICs is nearly fully ionized but with neutral cores that span a large range of H i masses and column densities and have negligible non-thermal broadening. We present predictions for their characteristic sizes and central column densities; the massive tail of the distribution should be within reach of future blind H i surveys. Local Group RELHICs (LGRs) have some properties consistent with observed Ultra Compact High Velocity Clouds (UCHVCs) but the sheer number of the latter suggests that most UCHVCs are not RELHICs. Our results suggest that LGRs (i) should typically be beyond 500 kpc from the Milky Way or M31; (ii) have positive Galactocentric radial velocities; (iii) H i sizes not exceeding 1 kpc, and (iv) should be nearly round. The detection and characterization of RELHICs would offer a unique probe of the small-scale clustering of CDM.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:15 November 2016
Date deposited:02 March 2017
Date of first online publication:17 November 2016
Date first made open access:02 March 2017

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