SIMBAD references

We present the results of a survey for intervening Mg II absorbers in the redshift range z ≃ 2-6 in the foreground of four high-redshift quasar spectra, 5.79 <= z_em <= 6.133, obtained with the European Southern Observatory Very Large Telescope X-Shooter. We visually identify 52 Mg II absorption systems and perform a systematic completeness and false positive analysis. We find 24 absorbers at >= 5σ significance in the equivalent width range 0.117 <= W₂₇₉₆ <= 3.655 Å with the highest redshift absorber at z = 4.89031 ± 4 x 10^–5. For weak (W₂₇₉₆ < 0.3 Å) systems, we measure an incidence rate dN/dz = 1.35 ± 0.58 at <z> = 2.34 and find that it almost doubles to dN/dz = 2.58 ± 0.67 by <z> = 4.81. The number of weak absorbers exceeds the number expected from an exponential fit to stronger systems (W₂₇₉₆ > 0.3 Å). We find that there must be significant evolution in the absorption halo properties of Mg II absorbers with W₂₇₉₆ > 0.1 Å by <z> = 4.77 and/or that they are associated with galaxies with luminosities beyond the limits of the current luminosity function at z ∼ 5. We find that the incidence rate of strong Mg II absorbers (W₂₇₉₆ > 1.0 Å) can be explained if they are associated with galaxies with L >= 0.29L_* and/or their covering fraction increases. If they continue to only be associated with galaxies with L >= 0.50L_* then their physical cross-section (σ_phys) increases from 0.015 Mpc² at z = 2.3-0.041 Mpc² at <z> = 4.77. We measure Ω_ Mg  II_ = 2.1^+6.3_–0.6×10^–8, 1.9^+2.9_–0.2 ×10^–8 and 3.9^+7.1_–2.4×10^–7 at <z> = 2.48, 3.41 and 4.77, respectively. At <z> = 4.77, Ω_ Mg  II_ exceeds the value expected from Ω_ H  I_ estimated from the global metallicity of damped Ly α systems (DLAs) at z ≃ 4.85 by a factor of ∼44 suggesting that either Mg II absorbers trace both ionized and neutral gas and/or are more metal rich than the average DLA at this redshift.