The ALHAMBRA survey: Estimation of the clustering signal encoded in the cosmic variance

Aims. The relative cosmic variance (σ<inf>v</inf>) is a fundamental source of uncertainty in pencil-beam surveys and, as a particular case of count-in-cell statistics, can be used to estimate the bias between galaxies and their underlying dark-matter distribution. Our goal is to test the significance of the clustering information encoded in the σ<inf>v</inf> measured in the ALHAMBRA survey. Methods. We measure the cosmic variance of several galaxy populations selected with B-band luminosity at 0.35 ≤ z < 1.05 as the intrinsic dispersion in the number density distribution derived from the 48 ALHAMBRA subfields. We compare the observational σ<inf>v</inf> with the cosmic variance of the dark matter expected from the theory, σ<inf>v,dm</inf>. This provides an estimation of the galaxy bias b. Results. The galaxy bias from the cosmic variance is in excellent agreement with the bias estimated by two-point correlation function analysis in ALHAMBRA. This holds for different redshift bins, for red and blue subsamples, and for several B-band luminosity selections. We find that b increases with the B-band luminosity and the redshift, as expected from previous work. Moreover, red galaxies have a larger bias than blue galaxies, with a relative bias of b<inf>rel</inf> = 1.4 ± 0.2. Conclusions. Our results demonstrate that the cosmic variance measured in ALHAMBRA is due to the clustering of galaxies and can be used to characterise the σ<inf>v</inf> affecting pencil-beam surveys. In addition, it can also be used to estimate the galaxy bias b from a method independent of correlation functions. © ESO, 2015.