The comoving mass density of Mg ii from z ∼ 2 to 5.5

Abstract

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 ESO 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≤W 2796 ≤3.655Å with the highest redshift absorber at z=4.89031±4×10 −5 . For weak (W 2796 <0.3Å) 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 (W 2796 >0.3Å). We find that there must be significant evolution in the absorption halo properties of Mg ii absorbers with W 2796 >0.1Å 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 (W 2796 >1.0Å) 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 Mpc 2 at z=2.3 to 0.041 Mpc 2 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 , 3.9 +7.1 −2.4 × 10 −7 at <z>=2.48, 3.41, 4.77, respectively. At <z>=4.77, Ω Mg ii exceeds the value expected from Ω H i estimated from the global metallicity of DLAs at z 4.85 by a factor of ∼44 suggesting that either Mg ii absorbers trace both ionised and neutral gas and/or are more metal rich than the average DLA at this redshift.

The CGM and IGM at z ∼ 5: metal budget and physical connection

“…We investigate four medium resolution and signal-to-noise spectra of z∼6 QSOs for the presence of C iv, Si iv doublets and associated transitions. These same spectra were investigated for the presence of Mg ii doublets in Codoreanu et al (2017).…”

“…We adjust for the likely contamination by false positive detections and varying completeness across redshift bins (see Section 3.4). We use the completeness adjusted values to compute (Equation 20) and fit (Equation 21) the column density distribution functions (CDDFs) of the Si iv and C iv systems identified in this work as well as the that of the Mg ii systems provided in Codoreanu et al (2017). The best Figure 10.…”

“…Absorption systems in the spectra of high redshift quasistelar objects (QSOs) present an opportunity to identify and study intervening metal enriched clouds during the first billion years of evolution of the Universe. Unambigous detection of these clouds is provided by the presence of doublets with high oscillator strength such as Mg ii Kacprzak et al 2012;Matejek & Simcoe 2012;Kacprzak et al 2013;Bosman et al 2017;Codoreanu et al 2017), Si iv (Boksenberg & Sargent perature/low density regions generally associated with the intergalactic medium (IGM) (eg. Schaye et al 2003Schaye et al , 2007Aguirre et al 2004, D'Odorico et al 2016Finlator et al 2016;Keating et al 2016;García et al 2017;Oppenheimer et al 2017).…”

The First Detection of a [C II] 158μm Emitter Associated with a Strong OI Absorber at the End of the Reionization Epoch

“…The physical and chemical properties of the circumgalactic medium (CGM) at z 6 have been studied successfully through the absorption in the spectra of background Quasi-Stellar Objects (QSOs) [1][2][3] . One of the most crucial questions is to investigate the nature and location of the source galaxies that give rise to these early metal absorbers [4][5][6] .…”

“…Metal absorption systems (e.g., O I, C IV, and Mg II) are powerful probes of the enrichment of the high-redshift intergalactic medium (IGM) [1][2][3] . Because the first excitation energies of O I and neutral hydrogen are almost identical, O I is considered one of the best indicators to trace the metal enrichment and the neutral IGM close to the reionization epoch 14,15 .…”