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We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d < 160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediate-redshift (z = 0.21−0.55) LRGs of stellar mass M star > 10 11 M . Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full H i Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually-matched components, we show that cool gas (T ∼ 10 4 K) density and metallicity can vary by more than a factor of ten in an LRG halo. Specifically, metal-poor absorbing components with < 1/10 solar metallicity are seen in 50% of the LRG halos, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent halos. We calculate the total surface mass density of cool gas, Σ cool , by applying the estimated ionization fraction corrections to the observed H i column densities. The radial profile of Σ cool is best-described by a projected Einasto profile of slope α = 1 and scale radius r s = 48 kpc. We find that typical LRGs at z ∼ 0.4 contain cool gas mass of M cool = (1 − 2) × 10 10 M at d < 160 kpc (or as much as M cool ≈ 4 × 10 10 M at d < 500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization O vi and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG halos.

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Despite extensive efforts, to date only two quasars have been found at z > 7, due to a combination of low spatial density and high contamination from more ubiquitous Galactic cool dwarfs in quasar selection. This limits our current knowledge of the supermassive black hole (SMBH) growth mechanism and reionization history. In this Letter, we report the discovery of a luminous quasar at z = 7.021, DELS J003836.10-152723.6 (hereafter J0038-1527), selected using photometric data from DESI Legacy imaging Survey (DELS), Pan-STARRS1 (PS1) imaging Survey, as well as Wide-field Infrared Survey Explore (WISE) mid-infrared all-sky survey. With an absolute magnitude of M 1450 =-27.1 and bolometric luminosity of L Bol =5.6×10 13 L , J0038-1527 is the most luminous quasar known at z > 7. Deep optical to near-infrared spectroscopic observations suggest that J0038-1527 hosts a 1.3 billion solar mass black hole accreting at the Eddington limit, with an Eddington ratio of 1.25±0.19. The C iv broad emission line of J0038-1527 is blueshifted by more than 3000 km s −1 relative to the quasar systemic redshift. More detailed investigations of the high-quality spectra reveal three extremely high-velocity C iv broad absorption lines (BALs) with velocity from 0.08 to 0.14 times the speed of light and total "balnicity" index of more than 5000 km s −1 , suggesting the presence of relativistic outflows. J0038-1527 is the first quasar found at the epoch of reionization (EoR) with such strong outflows, and therefore provides a unique labora-

We present a new Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) absorption-line survey to study halo gas around 16 luminous red galaxies (LRGs) at z = 0.21 − 0.55. The LRGs are selected uniformly with stellar mass M star > 10 11 M and no prior knowledge of the presence/absence of any absorption features. Based on observations of the full Lyman series, we obtain accurate measurements of neutral hydrogen column density N (H I) and find that high-N (H I) gas is common in these massive quiescent halos with a median of log N (H I) = 16.6 at projected distances d < ∼ 160 kpc. We measure a mean covering fraction of optically-thick gas with log N (H I) > ∼ 17.2 of κ LLS = 0.44 +0.12 −0.11 at d < ∼ 160 kpc and κ LLS = 0.71 +0.11 −0.20 at d < ∼ 100 kpc. The line-of-sight velocity separations between the H I absorbing gas and LRGs are characterized by a mean and dispersion of v gas−gal = 29 km s −1 and σ v gas−gal = 171 km s −1 . Combining COS far-ultraviolet and ground-based echelle spectra provides an expanded spectral coverage for multiple ionic transitions, from low-ionization Mg II and Si II, to intermediate ionization Si III and C III, and to highionization O VI absorption lines. We find that intermediate ions probed by C III and Si III are the most prominent UV metal lines in LRG halos with a mean covering fraction of κ(C III) 0.1 = 0.75 +0.08 −0.13 for W r (977) 0.1Å at d < 160 kpc, comparable to what is seen for C III in L * and sub-L * star-forming and red galaxies but exceeding Mg II or O VI in quiescent halos. The COS-LRG survey shows that massive quiescent halos contain widespread chemically-enriched cool gas and that little distinction between LRG and star-forming halos is found in their H I and C III content.