A Giant Shell of Ionized Gas Discovered near M82 with the Dragonfly Spectral Line Mapper Pathfinder

We present the discovery of a giant cloud ionized gas in field starbursting galaxy M82. Emission from is seen H$\alpha$ and [NII]$\lambda$6583 data obtained though small pathfinder instrument used to test key ideas that will be implemented Dragonfly Spectral Line Mapper, an upcoming ultranarrow-bandpass imaging version Telephoto Array. The discovered has shell-like morphology with linear extent $0.8^{\circ}$ positioned $0.6^{\circ}$ northwest At heliocentric distance M81 group, cloud's corresponds 55 kpc its projected nucleus M82 40 kpc. average surface brightness $2\times10^{-18}$ $\mathrm{erg} ~\mathrm{cm}^{-2} ~\mathrm{s}^{-1} ~\mathrm{arcsec}^{-2}$. [NII]$\lambda$6583/H$\alpha$ line ratio varies [NII]/H$\alpha$ $\sim0.2$ $\sim1.0$ across cloud, higher values found eastern end. Follow-up spectra Keck-LRIS confirm existence yield ratios = 0.340 $\pm$ 0.003 [SII]$\lambda$6716,6731/H$\alpha$ 0.64 0.03 cloud. This material could lifted by tidal interactions or powerful starburst. Alternatively, it may infalling cosmic web, potentially precipitated superwinds Deeper are needed these further. Mapper have 120 lenses, $40\times$ more than obtain presented here.