Exotic clouds in the local interstellar medium

Abstract

The neutral interstellar medium (ISM) inside the Local Bubble (LB) has been known to have properties typical of the warm neutral medium (WNM). However, several recent neutral hydrogen (HI) absorption experiments show evidence for the existence of at least several cold diffuse clouds inside or at the boundary of the LB, with properties highly unusual relative to the traditional cold neutral medium. These cold clouds have a low HI column density, and AU-scale sizes. As the kinematics of cold and warm gas inside the LB are similar, this suggests a possibility of all these different flavors of the local ISM belonging to the same interstellar flow. The co-existence of warm and cold phases inside the LB is exciting as it can be used to probe the thermal pressure inside the LB. In addition to cold clouds, several discrete screens of ionized scattering material are clearly located inside the LB. The cold exotic clouds inside the LB are most likely long-lived, and we expect many more clouds with similar properties to be discovered in the future with more sensitive radio observations. While physical mechanisms responsible for the production of such clouds are still poorly understood, dynamical triggering of phase conversion and/or interstellar turbulence are likely to play an important role.

10 pages, refereed, accepted for publication in the proceedings of the "From the Outer Heliosphere to the Local Bubble: Comparisons of New Observations with Theory" conference, Space Science Reviews

References in corpus (17)

• The Millennium Arecibo 21-CM Absorption Line Survey. II. Properties of the Warm and Cold Neutral Media
• Thermal condensation in a turbulent atomic hydrogen flow
• Faint Scattering Around Pulsars: Probing the Interstellar Medium on Solar System Size Scales
• The Diffuse Interstellar Clouds toward 23 Orionis
• Pulsar Parallaxes at 5 GHz with the Very Long Baseline Array
• On the Hydrodynamic Interaction of Shock Waves with Interstellar Clouds. II. The Effect of Smooth Cloud Boundaries on Cloud Destruction and Cloud Turbulence
• A Search for Larson-Type Relations in Numerical Simulations of the ISM. Evidence for Non-Constant Column Densities
• The History and Future of the Local and Loop I Bubbles
• Magnetically Dominated Strands of Cold Hydrogen in the Riegel-Crutcher Cloud
• On the structure of the turbulent interstellar atomic hydrogen. I- Physical characteristics
• Deflection of Pulsar Signal Reveals Compact Structures in the Galaxy
• Heliospheric Response to Different Possible Interstellar Environments
• A Cold Nearby Cloud Inside the Local Bubble
• The thinnest cold HI clouds in the diffuse interstellar medium?
• Tiny HI Clouds in the Local ISM
• Modeling of Interstellar Scintillation Arcs from Pulsar B1133+16
• Tiny HI Clouds in the Local ISM

Cited by in corpus (4)

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• Gaussian decomposition of HI surveys. V. Search for very cold clouds
• On the Geometry of the IBEX Ribbon
• Time-variability in the Interstellar Boundary Conditions of the Heliosphere: Effect of the Solar Journey on the Galactic Cosmic Ray Flux at Earth