The Local Hole: a galaxy under-density covering 90% of sky to ~200 Mpc

Jonathan H. W. Wong; T. Shanks; N. Metcalfe; J. R. Whitbourn

doi:10.1093/mnras/stac396

paper

The Local Hole: a galaxy under-density covering 90% of sky to ~200 Mpc

arXiv:2107.08505 · doi:10.1093/mnras/stac396

Abstract

We investigate the `Local Hole', an anomalous under-density in the local galaxy environment, by extending our previous galaxy $K -$ band number-redshift and number-magnitude counts to $\approx 90%$ of the sky. Our redshift samples are taken from the 2MASS Redshift Survey (2MRS) and the 2M++ catalogues, limited to $K < 11.5$ . We find that both surveys are in good agreement, showing an $\approx 21 - 22%$ under-density at $z < 0.075$ when compared to our homogeneous counts model that assumes the same luminosity function and other parameters as in our earlier papers. Using the Two Micron All Sky Survey (2MASS) for $n (K)$ galaxy counts, we measure an under-density relative to this model of $20 \pm 2%$ at $K < 11.5$ , which is consistent in both form and scale with the observed $n (z)$ under-density. To examine further the accuracy of the counts model, we compare its prediction for the fainter $n (K)$ counts of the Galaxy and Mass Assembly (GAMA) survey. We further compare these data with a model assuming the parameters of a previous study where little evidence for the Local Hole was found. At $13 < K < 16$ we find a significantly better fit for our model, arguing for our higher luminosity function normalisation. Although our implied under-density of $\approx 20%$ means local measurements of the Hubble Constant have been over-estimated by $\approx 3$ \%, such a scale of under-density is in tension with a global $Λ$ CDM cosmology at an $\approx 3 σ$ level.

arXiv comment14 pages, 12 figures, Accepted by MNRAS on 7th February, 2022, references updated for publication

The Local Hole: a galaxy under-density covering 90% of sky to ~200 Mpc

Abstract

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