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We use the Phoenix simulations to study the mass assembly history and internal structures of cluster dark matter haloes (⁠|$M_{200} \gtrsim 5\times 10^{14} h^{-1}{\rm M}_\odot$|⁠). We confirm that cluster haloes grow inside-out, similar to galactic haloes. Major merger events dominate the growth of the internal region and minor mergers/diffuse accretion shape the outskirts. However, compared to galactic haloes, cluster haloes tend to have a younger and more actively evolving inner region. On average, the majority of mass (⁠|$\gtrsim 80$| per cent) in the inner region (⁠|$R\lt 0.1 r_{200}$|⁠) of Phoenix haloes is accreted after |$z = 3$|⁠ , while for galactic haloes, most mass in the central region has already been accreted before |$z=6$|⁠. The density profiles of cluster haloes are less stable than those of galactic haloes over different radii. The enclosed mass within 50 or 150 kpc of all Phoenix haloes evolves substantially in the past |${\sim } 7$|  Gyr, while galactic haloes remained stable during the same period. We suggest that the relatively younger and more active state explains the various observations of cluster haloes, especially in central regions. [ABSTRACT FROM AUTHOR]

We use the 21-cm emission-line data from the Deep Investigation of Neutral Gas Origin-Very Large Array (DINGO-VLA) project to study the atomic hydrogen gas H  i of the Universe at redshifts z < 0.1. Results are obtained using a stacking analysis, combining the H  i signals from 3622 galaxies extracted from 267 VLA pointings in the G09 field of the Galaxy and Mass Assembly Survey (GAMA). Rather than using a traditional one-dimensional spectral stacking method, a three-dimensional cubelet stacking method is used to enable deconvolution and the accurate recovery of average galaxy fluxes from this high-resolution interferometric data set. By probing down to galactic scales, this experiment also overcomes confusion corrections that have been necessary to include in previous single-dish studies. After stacking and deconvolution, we obtain a 30σ H  i mass measurement from the stacked spectrum, indicating an average H  i mass of |${\rm{M_{\rm{{H}\,\small{I}}}}}=(1.67\pm 0.18)\times 10^{9}~{\rm{{\rm M}_{\odot }}}$|⁠. The corresponding cosmic density of neutral atomic hydrogen is |${\rm{\Omega _{\rm{{H}\,\small{I}}}}}=(0.38\pm 0.04)\times 10^{-3}$| at redshift of z = 0.051. These values are in good agreement with earlier results, implying there is no significant evolution of |$\Omega _{\rm{{H}\,\small{I}}}$| at lower redshifts. [ABSTRACT FROM AUTHOR]