The Giant Arc - Filament or Figment?

The so-called “Giant Arc” is a sparse pattern of MgII absorbers spanning approximately 740 comoving Mpc, whose discovery has been claimed to contradict the large-scale homogeneity inherent to the standard cosmological model. We previously showed that, with the same algorithm and parameters used for its discovery, very similar patterns are abundant in uniform random distributions, and among equivalent halo samples in a cosmological simulation of the standard model. In a response, the original discoverers of the “Giant Arc” have argued that these parameters were only appropriate for their specific observational data, but that a smaller linking length should be used for control studies, in which case far fewer patterns are detected. We briefly review and disprove these arguments, and demonstrate that large patterns like the “Giant Arc” are indeed ubiquitous in a statistically homogeneous universe.