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Abstract The Large Magellanic Cloud (LMC) has an extensive Hαemission halo that traces an extended, warm ionized component of its interstellar medium. Using the Wisconsin HαMapper telescope, we present the first kinematic Hαsurvey of an extensive region around the LMC, from (ℓ,b) = (264.°5, − 45.°5) to (295.°5, − 19.°5), covering +150 ≤v_LSR≤ + 390 km s⁻¹. We find that ionized hydrogen exists throughout the galaxy and extends several degrees beyond detected neutral hydrogen emission $(\log \left(N_{\mathrm{H}\mathrm{I}/{\mathrm{cm}}^{-2}}\right)\approx 18.3)$as traced by 21 cm in current surveys. Using the column density structure of the neutral gas and stellar line-of-sight depths as a guide, we estimate the upper limit mass of the ionized component of the LMC to be roughlyM_ionized≈ (0.6–1.8) × 10⁹M_☉, which is comparable to the total neutral atomic gas mass in the same region (M_neutral≈ 0.76–0.85 × 10⁹M_☉). Considering only the atomic phases, we findM_ionized/M_{ionized+neutral}, to be 46%–68% throughout the LMC and its extended halo. Additionally, we find an ionized gas cloud that extends off of the LMC at (ℓ,b) ≈ (285°, − 28°) into a region previously identified as the Leading Arm complex. This gas is moving at a similar line-of-sight velocity as the LMC and hasM_ionized/M_{ionized+neutral}= 13%–51%. This study, combined with previous studies of the SMC and extended structures of the Magellanic Clouds, continues to suggest that warm, ionized gas is as massive and dynamically important as the neutral gas in the Magellanic System. 

Optical emission lines are used to categorize galaxies into three groups according to their dominant central radiation source: active galactic nuclei, star formation, or low-ionization (nuclear) emission regions [LI(N)ERs] that may trace ionizing radiation from older stellar populations. Using the Wisconsin H-Alpha Mapper, we detect optical line emission in low-extinction windows within eight degrees of Galactic Center. The emission is associated with the 1.5-kiloparsec-radius “Tilted Disk” of neutral gas. We modify a model of this disk and find that the hydrogen gas observed is at least 48% ionized. The ratio [NII] λ6584 angstroms/Hα λ6563 angstroms increases from 0.3 to 2.5 with Galactocentric radius; [OIII] λ5007 angstroms and Hβ λ4861 angstroms are also sometimes detected. The line ratios for most Tilted Disk sightlines are characteristic of LI(N)ER galaxies.