Three-dimensional orientation of compact high velocity clouds

Heitsch, Fabian; Bartell, B.; Clark, Susan; Peek, J. E. G.; Cheng, Danny; Putman, Mary E.

doi:10.1093/mnrasl/slw124

Cited by 6 publications

(4 citation statements)

References 30 publications

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“…Its orbit is highly inclined and prograde, so that the Smith Cloud's v elocity relativ e to the ambient gas would expected to be much less than V tot . Heitsch et al ( 2016 ) proposed a method to reconstruct the three-dimensional cloud propagation direction required to calculate V tot , based on the cloud morphology in the position-velocity plane and v LSR . Applying the method to a subset of clouds identified in HIPASS (Putman et al 2002 ), they estimate V tot of up to > 300 km s −1 for a few clouds.…”

Section: Impact Velocitymentioning

confidence: 99%

Mass, morphing, metallicities: the evolution of infalling high velocity clouds

Heitsch

Marchal

Miville-Deschênes

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We revisit the reliability of metallicity estimates of high velocity clouds with the help of hydrodynamical simulations. We quantify the effect of accretion and viewing angle on metallicity estimates derived from absorption lines. Model parameters are chosen to provide strong lower limits on cloud contamination by ambient gas. Consistent with previous results, a cloud traveling through a stratified halo is contaminated by ambient material to the point that <10 per cent of its mass in neutral hydrogen consists of original cloud material. Contamination progresses nearly linearly with time, and it increases from head to tail. Therefore, metallicity estimates will depend on the evolutionary state of the cloud, and on position. While metallicities change with time by more than a factor of 10, well beyond observational uncertainties, most lines-of-sight range only within those uncertainties at any given time over all positions. Metallicity estimates vary with the cloud’s inclination angle within observational uncertainties. The cloud survives the infall through the halo because ambient gas continuously condenses and cools in the cloud’s wake and thus appears in the neutral phase. Therefore, the cloud observed at any fixed time is not a well-defined structure across time, since material gets constantly replaced. The thermal phases of the cloud are largely determined by the ambient pressure. Internal cloud dynamics evolve from drag gradients caused by shear instabilities, to complex patterns due to ram-pressure shielding, leading to a peloton effect, in which initially lagging gas can catch up to and even overtake the head of the cloud.

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Section: Impact Velocitymentioning

confidence: 99%

Mass, morphing, metallicities: the evolution of infalling high velocity clouds

Heitsch

Marchal

Miville-Deschênes

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…In the theory of turbulent fragmentation, cores form in layers assembled at the convergence of large-scale flows or in shells swept up by expanding nebulae such as HII regions, stellar wind bubbles and supernova remnants. Numerical simulations indicate that these cores are delivered by a complex interplay between shocks, thermal instabil-ity, self-gravity and magnetic fields, moderated by thermal and chemical microphysics and radiation transfer (Bhattal et al, 1998;Klessen, 2001;Bonnell, 2005, 2006;Vázquez-Semadeni et al, 2007;Padoan et al, 2007;Banerjee et al, 2009;Heitsch et al, 2011;Walch et al, 2012). Due to the anisotropies introduced by shocks, magnetic fields, and self-gravity, these layers and shells tend to break up first into filaments from which cores then condense, in particular at the places where filaments intersect.…”

Section: Phenomenology Of Core Growth Collapse and Fragmentationmentioning

confidence: 99%

The Origin and Universality of the Stellar Initial Mass Function

Offner¹,

Clark²,

Hennebelle³

et al. 2014

Protostars and Planets VI

121

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We review current theories for the origin of the Stellar Initial Mass Function (IMF) with particular focus on the extent to which the IMF can be considered universal across various environments. To place the issue in an observational context, we summarize the techniques used to determine the IMF for different stellar populations, the uncertainties affecting the results, and the evidence for systematic departures from universality under extreme circumstances. We next consider theories for the formation of prestellar cores by turbulent fragmentation and the possible impact of various thermal, hydrodynamic and magneto-hydrodynamic instabilities. We address the conversion of prestellar cores into stars and evaluate the roles played by different processes: competitive accretion, dynamical fragmentation, ejection and starvation, filament fragmentation and filamentary accretion flows, disk formation and fragmentation, critical scales imposed by thermodynamics, and magnetic braking. We present explanations for the characteristic shapes of the Present-Day Prestellar Core Mass Function and the IMF and consider what significance can be attached to their apparent similarity. Substantial computational advances have occurred in recent years, and we review the numerical simulations that have been performed to predict the IMF directly and discuss the influence of dynamics, time-dependent phenomena, and initial conditions.Comment: 24 pages, 6 figures. Accepted for publication as a chapter in Protostars and Planets VI, University of Arizona Press (2014), eds. H. Beuther, R. S. Klessen, C. P. Dullemond, Th. Hennin

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“…Clearly, modeling the connections would require further investigation, notably the determination of the 3D orientation of complex C and its neighbors (Heitsch et al 2016). A locus of velocities and distances might also constrain the "orbits" of the gas complexes (e.g., Lockman et al 2008, for the Smith Cloud) and possible related galactic progenitors.…”

Section: Large-scale View From Ebhismentioning

confidence: 99%

Resolving the formation of cold HI filaments in the high velocity cloud complex C

Marchal,

Martin,

Gong

2021

Preprint

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The physical properties of galactic halo gas have a profound impact on the life cycle of galaxies. As gas travels through a galactic halo, it undergoes dynamical interactions, influencing its impact on star formation and the chemical evolution of the galactic disk. In the Milky-Way halo, considerable effort has been made to understand the spatial distribution of neutral gas, which are mostly in the form of large complexes. However, the internal variations of their physical properties remains unclear. In this study, we investigate the thermal and dynamical state of the neutral gas in high velocity clouds (HVCs). High-resolution observations (1. 1) of the 21 cm line emission in the EN field of the DHIGLS H I survey are used to analyze the physical properties of the bright concentration C I B located at an edge of a large HVC complex, complex C. We use the Gaussian decomposition code ROHSA to model the multiphase content of C I B, and perform a power spectrum analysis to analyze its multi-scale structure. Physical properties of some 200 structures extracted using dendrograms are examined. Each phase exhibits different thermal and turbulent properties. We identify two distinct regions, one of which has a prominent protrusion extending from the edge of complex C that exhibits an ongoing phase transition from warm diffuse gas to cold dense gas and filaments. The scale at which the warm gas becomes unstable and undergoes a thermal condensation is about 15 pc, corresponding to a cooling time about 1.5 Myr. Our study characterizes the statistical properties of turbulence in the fluid of a HVC for the first time. We find that a transition from subsonic to trans-sonic turbulence is associated with the thermal condensation, going from large to small scales. A large scale perspective of complex C suggests that hydrodynamic instabilities are involved in creating the structured concentration C I B and the phase transition therein. However, the details of the dynamical and thermal processes remain unclear and will require further investigation, through both observations and numerical simulations.

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Three-dimensional orientation of compact high velocity clouds

Cited by 6 publications

References 30 publications

Mass, morphing, metallicities: the evolution of infalling high velocity clouds

Mass, morphing, metallicities: the evolution of infalling high velocity clouds

The Origin and Universality of the Stellar Initial Mass Function

Resolving the formation of cold HI filaments in the high velocity cloud complex C

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