IONIZED GAS IN THE SMITH CLOUD

Abstract

Abstract. We present WHAM observations of Hα, [N II], and [S II] in the Smith Cloud. A map of Hα emission from the cloud shows ionized gas coincident with the brightest H I emission, but nearly-as-bright Hα in some regions with faint H I. The ionized mass of the cloud is at least as large as the neutral mass,> 10 6 M⊙. Ionized gas in the core of the Smith Cloud has an electron temperature 6000 K < T < 16000 K. The observed ratio [N II]/Hα = 0.39 ± 0.09 shows that the cloud has a non-primordial nitrogen abundance, 0.1 − 1 × solar. The Smith Cloud is a high velocity cloud with a radial velocity near +100 km s −1 located at (l, b) = (40 ◦ , −14 ◦). Lockman et al. (2008) presented an H I survey of the cloud using the Green Bank Telescope. They indicate that the cloud is interacting with gas in the Galactic disk. The cloud has a cometary morphology with a bright core and a diffuse, trailing tail. Bland-Hawthorn et al. (1998) and Putman et al. (2003) obtained Hα, [O III] λ5007, and [N II] λ6548 Fabry-Perot spectra of two 5 ’ fields in the core of the cloud. They detected emission from the