Arguments against using h-1 Mpc units in observational cosmology

It is common to express cosmological measurements in units of h(-1) Mpc. Here, we review some of the complications that originate from this practice. A crucial problem caused by these units is related to the normalization of the matter power spectrum, which is commonly characterized in terms of the linear-theory rms mass fluctuation in spheres of radius 8 h(-1) Mpc, sigma(8). This parameter does not correctly capture the impact of h on the amplitude of density fluctuations. We show that the use of sigma(8) has caused critical misconceptions for both the so-called sigma(8) tension regarding the consistency between low-redshift probes and cosmic microwave background data and the way in which growth-rate estimates inferred from redshift-space distortions are commonly expressed. We propose to abandon the use of h(-1) Mpc units in cosmology and to characterize the amplitude of the matter power spectrum in terms of sigma(12), defined as the mass fluctuation in spheres of radius 12 Mpc, whose value is similar to the standard sigma(8) for h similar to 0.67.