Simulations of High-Velocity Clouds. I. Hydrodynamics and High-Velocity High Ions

Abstract

We present hydrodynamic simulations of high-velocity clouds (HVCs) traveling through the hot, tenuous medium in the Galactic halo. A suite of models was created using the FLASH hydrodynamics code, sampling various cloud sizes, densities, and velocities. In all cases, the cloud-halo interaction ablates material from the clouds. The ablated material falls behind the clouds, where it mixes with the ambient medium to produce intermediate-temperature gas, some of which radiatively cools to less than 10,000 K. Using a non-equilibrium ionization (NEI) algorithm, we track the ionization levels of carbon, nitrogen, and oxygen in the gas throughout the simulation period. We present observation-related predictions, including the expected H I and high ion (C IV, N V, and O VI) column densities on sight lines through the clouds as functions of evolutionary time and off-center distance. The predicted column densities overlap those observed for Complex C. The observations are best matched by clouds that have interacted with the Galactic environment for tens to hundreds of megayears. Given the large distances across which the clouds would travel during such time, our results are consistent with Complex C having an extragalactic origin. The destruction of HVCs is also of interest; the smallest cloud (initial mass \approx 120 Msun) lost most of its mass during the simulation period (60 Myr), while the largest cloud (initial mass \approx 4e5 Msun) remained largely intact, although deformed, during its simulation period (240 Myr).

20 pages, 13 figures. Accepted for publication in the Astrophysical Journal

References in corpus (16)

• Time-Dependent Ionization in Radiatively Cooling Gas
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• Turbulent Structure of a Stratified Supernova-Driven Interstellar Medium
• Distances to Galactic high-velocity clouds. Complex C
• X-Ray Absorption from the Milky Way Halo and the Local Group
• An Accurate Distance to High-Velocity Cloud Complex C
• A Survey of O VI, C III, and H I in Highly Ionized High-Velocity Clouds
• Numerical Study of Turbulent Mixing Layers with Non-Equilibrium Ionization Calculations
• Metallicity and Ionization in High Velocity Cloud Complex C
• X-ray and UV spectroscopy of Galactic diffuse hot gas along the LMC X--3 sight line
• Xmm-Newton Observations of the Diffuse X-ray Background
• The evolution of interstellar clouds in a streaming hot plasma including heat conduction
• Reconstructing Deconstruction: High-Velocity Cloud Distance Through Disruption Morphology
• MHD Turbulent Mixing Layers: Equilibrium Cooling Models
• Evaporation and condensation of spherical interstellar clouds. Self-consistent models with saturated heat conduction and cooling
• Determining The Galactic Halo's Emission Measure from UV and X-ray Observations

Cited by in corpus (55)

• Gaseous Galaxy Halos
• A Characteristic Scale for Cold Gas
• The Launching of Cold Clouds by Galaxy Outflows I: Hydrodynamic Interactions with Radiative Cooling
• The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies
• The Magellanic Stream: Circumnavigating the Galaxy
• The survival of gas clouds in the Circumgalactic Medium of Milky Way-like galaxies
• Physics of the Galactic Center Cloud G2, on its Way towards the Super-Massive Black Hole
• Quasars Probing Quasars VII. The Pinnacle of the Cool Circumgalactic Medium Surrounds Massive z~2 Galaxies
• A Universal Density Structure for Circum-Galactic Gas
• Simulations of radiative turbulent mixing layers
• High-velocity clouds as streams of ionized and neutral gas in the halo of the Milky Way
• Gas Accretion via Condensation and Fountains
• Radiative Mixing Layers: Insights from Turbulent Combustion
• Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane
• QSO Absorption Systems Detected in Ne VIII: High-Metallicity Clouds with a Large Effective Cross Section
• The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results from the COS-GASS+COS-Halos Surveys
• Viscous Kelvin-Helmholtz instabilities in highly ionised plasmas
• Hydrodynamical simulations of a compact source scenario for the Galactic Center cloud G2
• On the dynamics and survival of fractal clouds in galactic winds
• Mixing of Clumpy Supernova Ejecta into Molecular Clouds
• The turbulent destruction of clouds - III. Three dimensional adiabatic shock-cloud simulations
• HST/COS Observations of Ionized Gas Accretion at the Disk-halo Interface of M33
• Cos observations of metal line and broad lyman alpha absorption in the multi-phase o vi and ne viii system toward he 02226-4110
• The High-Ion Content and Kinematics of Low-Redshift Lyman Limit Systems
• Cloudy with A Chance of Rain: Accretion Braking of Cold Clouds
• Magnetized Gas in the Smith High Velocity Cloud
• The Magellanic System: the puzzle of the leading gas stream
• Gas Accretion onto the Milky Way
• Mixing between High Velocity Clouds and the Galactic Halo
• OVI Traces Photoionized Streams With Collisionally Ionized Boundaries in Cosmological Simulations of $z\sim 1$ Massive Galaxies
• Alone on a wide wide sea. The origin of SECCO 1, an isolated star-forming gas cloud in the Virgo cluster
• Si iv Column Densities Predicted from Non-Equilibrium Ionization Simulations of Turbulent Mixing Layers and High-Velocity Clouds
• Mass, Morphing, Metallicities: The Evolution of Infalling High Velocity Clouds
• Understanding Galaxy Outflows as the Product of Unstable Turbulent Support
• Simulating Gas Inflow at the Disk-Halo Interface
• The Anatomy of a Turbulent Radiative Mixing Layer: Insights from an Analytic Model with Turbulent Conduction and Viscosity
• The Effect of Mixing on the Observed Metallicity of the Smith Cloud
• Simulations of High-Velocity Clouds. II. Ablation from High-Velocity Clouds as a Source of Low-Velocity High Ions
• Column Density Profiles of Cold Clouds Driven by Galactic Outflows
• Probing the Structure and Kinematics of the transition Layer between the Magellanic Stream and the Halo in HI
• High-ion absorption in the proximate damped Lyman-alpha system toward Q0841+129
• The discovery of the largest gas filament in our Galaxy, or a new spiral arm?
• Exploring Hydrodynamic Instabilities along the Infalling High-Velocity Cloud Complex A
• Modeling the X-rays Resulting from High Velocity Clouds
• R-process Rain from Binary Neutron Star Mergers in the Galactic Halo
• On the Origin of High-velocity Clouds in the Galaxy
• The Origin of the X-ray Emission from the High-velocity Cloud MS30.7-81.4-118
• The Long Tails of the Pegasus-Pisces Arch Intermediate Velocity Cloud
• Distant probes of RM structure -- Where is the Faraday Rotation towards the Magellanic Leading Arm?
• In Search of an Interface between Warm and Hot Gas within the Local Bubble
• Hydrodynamics of Clustered Clouds: Drafting, Survival, Condensation, and Ablation
• Cosmic Rays and Non-thermal Emission Induced by Accretion of Cool Gas onto the Galactic Disk
• Estimating the Fuel Supply Rate on the Galactic Disk from High Velocity Clouds (HVCs) Infall
• The Observed O VI is Just the Tip of the Iceberg: Estimating the Hidden Material in Circumgalactic and Intergalactic Clouds
• Non-thermal emission from fall-back clouds in the Broad-Line Region of Active Galactic Nuclei