The Diffuse Ionized Gas of the Large Magellanic Cloud

The Large Magellanic Cloud (LMC) has an extensive H${}_{\alpha }$ emission halo that traces an extended, warm ionized component of its interstellar medium. Using the Wisconsin H${}_{\alpha }$ Mapper (WHAM) telescope, we present the first kinematic \ha\ survey of an extensive region around the LMC, from $l,b=(264\mathrm{°}.5,-45\mathrm{°}.5)$ to $(295\mathrm{°}.5,-19\mathrm{°}.5)$, covering $+150\le v_{lsr}\le +390km{s}^{-1}$. We find that ionized hydrogen exists throughout the galaxy and extends several degrees beyond detected neutral hydrogen emission $(\log \left(N_{{\mathrm{H}}_{\mathrm{I}}\mathrm{/}\mathrm{c}{\mathrm{m}}^{-2}}\right)\approx 18.3)$ 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 roughly $M_{\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{i}\mathrm{z}\mathrm{e}\mathrm{d}}\approx (0.6-1.8)\times {10}^9{\mathrm{M}}_{sun}$, which is comparable to the total neutral atomic gas mass in the same region ($M_{\mathrm{n}\mathrm{e}\mathrm{u}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{l}}\approx 0.75-0.85\times {10}^9{\mathrm{M}}_{sun}$). Considering only the atomic phases, we find $M_{\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{i}\mathrm{z}\mathrm{e}\mathrm{d}}\mathrm{/}{M}_{\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{i}\mathrm{z}\mathrm{e}\mathrm{d}+\mathrm{n}\mathrm{e}\mathrm{u}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{l}}$, 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 $l,b\approx (285\mathrm{°},-28\mathrm{°})$ 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 has $M_{\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{i}\mathrm{z}\mathrm{e}\mathrm{d}}\mathrm{/}{M}_{\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{i}\mathrm{z}\mathrm{e}\mathrm{d}+\mathrm{n}\mathrm{e}\mathrm{u}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{l}}=$ 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.$