Evidence for Azimuthally Anisotropic MgII Absorption around DESI Luminous Red Galaxies

We use DESI DR1 luminous red galaxies (LRGs) and background quasar spectra to measure the mean MgII equivalent-width field around massive quiescent galaxies as a function of projected radius and azimuth relative to the projected major axis. Our forced-measurement approach assigns a MgII doublet-window EW to every LRG-quasar pair, including spectra without individually detected absorbers, and subtracts a redshift-matched random-control signal measured from the same normalized quasar spectra. The all-angle profile declines smoothly over r p=0.01 - 1.0 proper Mpc and shows stronger inner absorption at 0.4<z LRG<0.75 than at 0.75<z LRG<1.1. Superposed on this radial and redshift dependence, sightlines near the LRG major axis show enhanced absorption relative to the minor axis at r p 30 - 80 kpc. For the full 0.4<z LRG<1.1 sample, the integrated fiducial major-minus-minor difference over r p=0.03 - 0.077 Mpc is 0.184 plus or minus0.075 Angstrom, with a position-angle randomization probability p=0.013. The redshift split shows no significant evolution in the anisotropy amplitude, even though the inner EW profile itself evolves. This DESI DR1 measurement provides evidence for a localized major-axis enhancement of MgII-bearing cool/warm gas around LRGs, showing that azimuthal CGM structure is measurable in massive quiescent halos as well as in star-forming systems.