Ionized Gas in the Smith Cloud

Abstract

We present Wisconsin H-Alpha Mapper observations of ionized gas in the Smith Cloud, a high velocity cloud which Lockman et al. have recently suggested is interacting with the Galactic disk. Our H-alpha map shows the brightest H-alpha emission, 0.43 \pm 0.04 R, coincident with the brightest H I, while slightly fainter H-alpha emission (0.25 \pm 0.02 R) is observed in a region with H I intensities < 0.1 times as bright as the brightest H I. We derive an ionized mass of \gtrsim 3 \times 10^6 M_\odot, comparable to the H I mass, with the H^+ mass spread over a considerably larger area than the H I. An estimated Galactic extinction correction could adjust these values upwards by 40 %. H-alpha and [S II] line widths towards the region of brightest emission constrain the electron temperature of the gas to be between 8000 K and 23000 K. A detection of [N II] λ6583 in the same direction with a line ratio [N II] / H-alpha = 0.32 \pm 0.05 constrains the metallicity of the cloud: for typical photoionization temperatures of 8000-12000 K, the nitrogen abundance is 0.15-0.44 times solar. These results lend further support to the claim that the Smith Cloud is new material accreting onto the Galaxy.

8 pages, 4 figures, ApJ accepted. This is the ApJ version of work presented in an early form as Hill et al 2009a (arxiv:0901.0712)

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• Reconstructing Deconstruction: High-Velocity Cloud Distance Through Disruption Morphology
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Cited by in corpus (41)

• Gaseous Galaxy Halos
• Fuel Efficient Galaxies: Sustaining Star Formation with Stellar Mass Loss
• High-velocity clouds as streams of ionized and neutral gas in the halo of the Milky Way
• GASKAP -- The Galactic ASKAP Survey
• Photoionization of High Altitude Gas in a Supernova-Driven Turbulent Interstellar Medium
• On the Metallicity and Origin of the Smith High-Velocity Cloud
• Warm Ionized Gas Revealed in the Magellanic Bridge Tidal Remnant: Constraining the Baryon Content and the Escaping Ionizing Photons around Dwarf Galaxies
• The Smith Cloud: high-velocity accretion and dark-matter confinement
• An absorption-selected survey of neutral gas in the Milky Way halo
• Magnetized Gas in the Smith High Velocity Cloud
• Detection of a Coherent Magnetic Field in the Magellanic Bridge through Faraday Rotation
• Gas Accretion onto the Milky Way
• Constraining the Magnetic Field of the Smith High Velocity Cloud using Faraday rotation
• Revealing the Ionization Properties of the Magellanic Stream using Optical Emission
• Collisions between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud
• Magnetized High Velocity Clouds in the Galactic Halo: A New Distance Constraint
• Mixing between High Velocity Clouds and the Galactic Halo
• A Radio Polarisation Study of Magnetic Fields in the Small Magellanic Cloud
• Present-day Galactic Evolution: Low-metallicity, Warm, Ionized Gas Inflow Associated with High-Velocity Cloud Complex A
• Simulating Gas Inflow at the Disk-Halo Interface
• Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud
• The Smith Cloud: surviving a high speed transit of the Galactic disc
• A Search For Star Formation in the Smith Cloud
• The Effect of Mixing on the Observed Metallicity of the Smith Cloud
• The Diffuse Ionized Gas Halo of the Small Magellanic Cloud
• Simulations of High-Velocity Clouds. II. Ablation from High-Velocity Clouds as a Source of Low-Velocity High Ions
• Caught in the Act: A Metal-Rich High-Velocity Cloud in the Inner Galaxy
• Mapping the Supernovae Driven Winds of the Large Magellanic Cloud in H$\alpha$ Emission I
• H$\alpha$ Distances to the Leading Arm of the Magellanic Stream
• Simulating the impact of the Smith Cloud
• Exploring Hydrodynamic Instabilities along the Infalling High-Velocity Cloud Complex A
• Revealing the Faraday Depth Structure of Radio Galaxy NGC 612 with Broad-Band Radio Polarimetric Observations
• The Diffuse Ionized Gas of the Large Magellanic Cloud
• Three-Dimensional Orientation of Compact High Velocity Clouds
• Properties of 3D HI Filaments in the Smith High Velocity Cloud
• Significant foreground unrelated non-acoustic anisotropy on the one degree scale in WMAP 5-year observations
• A Component of the Smith High Velocity Cloud Now Crossing the Galactic Plane
• Tracing dense and diffuse neutral hydrogen in the halo of the Milky Way
• Neutral Gas Accretion onto Nearby Galaxies
• Accretion Onto the Milky Way: The Smith Cloud
• Simulating High-Velocity Clouds in the Observational Plane: An Initial Study with the Smith Cloud