Dynamic interactions between the two Magellanic Clouds have flung large quantities of gas into the halo of the Milky Way. The result is a spectacular arrangement of gaseous structures including the Magellanic Stream, the Magellanic Bridge, and the Leading Arm (collectively referred to as the Magellanic System). In this third paper of a series studying the Magellanic gas in absorption, we analyze the gas ionization level using a sample of 69 Hubble Space Telescope/Cosmic Origins Spectrograph sightlines that pass through or within 30 • of the 21 cm-emitting regions. We find that 81% (56/69) of the sightlines show UV absorption at Magellanic velocities, indicating that the total cross section of the Magellanic System is ≈11 000 square degrees, or around a quarter of the entire sky. Using observations of the Si III/Si II ratio together with Cloudy photoionization modeling, we calculate the total gas mass (atomic plus ionized) of the Magellanic System to be ≈2.0×10 9 M ⊙ (d/55 kpc) 2 , with the ionized gas contributing around three times as much mass as the atomic gas. This is larger than the current-day interstellar H I mass of both Magellanic Clouds combined, indicating that they have lost most of their initial gas mass. If the gas in the Magellanic System survives to reach the Galactic disk over its inflow time of ∼0.5-1.0 Gyr, it will represent an average inflow rate of ∼3.7-6.7 M ⊙ yr −1 , potentially raising the Galactic star formation rate. However, multiple signs of an evaporative interaction with the hot Galactic corona indicate that the Magellanic gas may not survive its journey to the disk fully intact, and will instead add material to (and cool) the corona.

We use Keck/HIRES spectra of 37 optically bright quasars at z = 2-4 to study narrow absorption lines that are intrinsic to the quasars (intrinsic NALs, produced in gas that is physically associated with the quasar central engine). We identify 150 NAL systems, that contain 124 C IV, 12 N V, and 50 Si IV doublets, of which 18 are associated systems (within 5,000 km s −1 of the quasar redshift). We use partial coverage analysis to separate intrinsic NALs from NALs produced in cosmologically intervening structures. We find 39 candidate intrinsic systems, (28 reliable determinations and 11 that are possibly intrinsic). We estimate that 10-17% of C IV systems at blueshifts of 5,000-70,000 km s −1 relative to quasars are intrinsic. At least 32% of quasars contain one or more intrinsic C IV NALs. Considering N V and Si IV doublets showing partial coverage as well, at least 50% of quasars host intrinsic NALs. This result constrains the solid angle subtended by the absorbers to the background source(s). We identify two families of intrinsic NAL systems, those with strong N V absorption, and those with negligible absorption in N V, but with partial coverage in the C IV doublet. We discuss the idea that these two families represent different regions or conditions in accretion disk winds. Of the 26 intrinsic C IV NAL systems, 13 have detectable low-ionization absorption lines at similar velocities, suggesting that these are two-phase structures in the wind rather than absorbers in the host galaxy. We also compare possible models for quasar outflows, including radiatively accelerated disk-driven winds, magnetocentrifugally accelerated winds, and pressure-driven winds, and we discuss ways of distinguishing between these models observationally.

We present results from a survey of weak Mg ii absorbers in the VLT/UVES spectra of 81 QSOs obtained from the ESO archive. In this survey, we identified 112 weak Mg ii systems within the redshift interval 0:4 < z < 2:4 with 86% completeness down to a rest-frame equivalent width of W r (2796) ¼ 0:02 8, covering a cumulative redshift path length of ÁZ $ 77:3. From this sample, we estimate that the number of weak absorbers per unit redshift (dN/dz) increases from 1:06 AE 0:04 at z h i ¼ 1:9 to 1:76 AE 0:08 at z h i ¼ 1:2 and thereafter decreases to 1:51 AE 0:09 at z h i ¼ 0:9 and 1:06 AE 0:10 at z h i ¼ 0:6. Thus, we find evidence for an evolution in the population of weak Mg ii absorbers, with their number density peaking at z ¼ 1:2. We also determine the equivalent width distribution of weak systems at z h i ¼ 0:9 and z h i ¼ 1:9. At 0:4 < z < 1:4, there is evidence for a turnover from a power law of the form n(W r ) / W À1:04 r at W r (2796) < 0:1 8. This turnover is more extreme at 1:4 < z < 2:4, where the equivalent width distribution is close to an extrapolation of the exponential distribution function found for strong Mg ii absorbers. Based on these results, we discuss the possibility that some fraction of weak Mg ii absorbers, particularly single cloud systems, are related to satellite clouds surrounding strong Mg ii systems. These structures could also be analogs to Milky Way high-velocity clouds. In this context, the paucity of high-redshift weak Mg ii absorbers is caused by a lack of isolated clouds accreting onto galaxies during that epoch.

We carried out a target survey for Lyman break galaxies (LBGs) and Ly emitters (LAEs) around QSO SDSS J0211À0009 at z ¼ 4:87. The deep and wide broadband and narrowband imaging simultaneously revealed the perspective structure of these two high-z populations. The LBGs without Ly emission form a filamentary structure including the QSO, while the LAEs are distributed around the QSO but avoid it within a distance of $4.5 Mpc. On the other hand, we serendipitously discovered a protocluster with a significant concentration of LBGs and LAEs, where no strongly UV ionizing source, such as a QSO or radio galaxy, is known to exist. In this cluster field, the two populations are spatially cross-correlated with each other. The relative spatial distribution of LAEs to LBGs in the QSO field is in stark contrast to that in the cluster field. We also found a weak trend showing that the number counts based on Ly and UV continuum fluxes of LAEs in the QSO field are slightly lower than in the cluster field, whereas the number counts of LBGs are almost consistent with each other. The LAEs avoid the nearby region around the QSO where the local UV background radiation could be $100 times stronger than the average for the epoch. The clustering segregation between LBGs and LAEs seen in the QSO field could be due to either enhanced early galaxy formation in an overdense environment, causing all the LAEs to evolve into LBGs, or local photoionization due to the strong UV radiation from the QSO, effectively causing a deficit in low-mass galaxies like LAEs. Subject headingg s: cosmology: observations -galaxies: high-redshift -large-scale structure of universe

Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, α. A smaller sample of higher signal-to-noise ratio spectra, with dedicated calibration, would allow a detailed test of this evidence. Towards that end, we observed equatorial quasar HS 1549+1919 with three telescopes: the Very Large Telescope, Keck and, for the first time in such analyses, Subaru. By directly comparing these spectra to each other, and by 'supercalibrating' them using asteroid and iodine-cell tests, we detected and removed long-range distortions of the quasar spectra's wavelength scales which would have caused significant systematic errors in our α measurements. For each telescope we measure the relative deviation in α from the current laboratory value, ∆α/α, in 3 absorption systems at redshifts z abs = 1.143, 1.342, and 1.802. The nine measurements of ∆α/α are all consistent with zero at the 2-σ level, with 1-σ statistical (systematic) uncertainties 5.6-24 (1.8-7.0) parts per million (ppm). They are also consistent with each other at the 1-σ level, allowing us to form a combined value for each telescope and, finally, a single value for this line of sight: ∆α/α = −5.4 ± 3.3 stat ± 1.5 sys ppm, consistent with both zero and previous, large samples. We also average all Large Programme results measuring ∆α/α = −0.6±1.9 stat ±0.9 sys ppm. Our results demonstrate the robustness and reliability at the 3 ppm level afforded by supercalibration techniques and direct comparison of spectra from different telescopes.