Striations, wisps and arcs - the fascinating evolution of filaments in a violent environment

多相星际介质（ISM）由一个复杂的致密冷丝状结构网络组成，这些结构嵌入在弥散的、较热的介质中。这些细丝被认为是由星际湍流、大尺度旋臂或引力盘不稳定造成的压缩、汇聚流形成的。一般认为，一旦它们凝聚成恒星，就会被摧毁，恒星通过电离辐射和恒星风驱散它们的环境。到目前为止，细丝通常被视为孤立的、均匀的结构。然而，最近的观察表明，细丝比目前所认为的要复杂得多。已经检测到不规则的内部速度场，表明细丝实际上是一束狭窄的相互作用的弦。此外，最近的新观测表明，细丝经常嵌入大规模的气流中，这强烈地影响了它们的演化。这些流动来自附近的恒星形成区域，产生剧烈的外流，将低密度的温暖和高温气体喷射到星系环境中。我们建议研究致密气体细丝与附近恒星形成区域产生的周围风的相互作用。我们想要探索灯丝内部密度场和湍流速度结构如何受到其与风的相互作用的影响，从而导致相互作用区内的流体动力学不稳定性（例如开尔文-亥姆霍兹），并将密度波驱动到灯丝内部区域。这些相互作用可以解释观测到的复杂速度结构。此外，它可以触发恒星形成，但也可以在恒星形成之前通过将冷而致密的丝状气体与弥漫的，更热的风物质混合而破坏灯丝的部分。作为一个极好的测试案例，我们将重点关注Alves等人最近在蛇夫座的巴纳德44灯丝中发现的迷人的亚结构。我们的研究结果将为分子云的基本组成部分——细丝的演化提供重要信息，特别是它们与周围湍流和剧烈的环境之间的密切耦合。

The multi-phase interstellar medium (ISM) consists of a complex network of dense and cold filamentary structures that are embedded in a diffuse, hotter medium. The filaments are believed to form by compressional, converging flows as a result of interstellar turbulence, by large scale spiral arms or by gravitational disk instabilities. It is generally believed that they are destroyed as soon as they condense into stars which disperse their environment by their ionizing radiation and stellar winds. Up until now, filaments have often been treated as isolated, homogeneous structures. However, recent observations indicate that filaments are much more complex than assumed so far. Irregular internal velocity fields have been detected indicating that filaments are actually bundles of narrow, interacting strings. In addition, new recent observations show that filaments are often embedded in large-scale gas flows that strongly affect their evolution. These flows result from nearby star-forming regions that generate violent outflows, ejecting low-density warm and hot gas into the galactic environment. We propose to investigate the interaction of dense gas filaments with surrounding winds, generated by nearby star-forming regions. We want to explore how the internal density field and turbulent velocity structure of a filament is affected by its interaction with the wind that leads to hydrodynamical instabilities (e.g. Kelvin-Helmholtz) in the interaction zone and drives density waves into the inner filamentary region. These interactions may explain the complex velocity structure observed. In addition, it can trigger star formation but also could destroy segments of a filament prior to star formation by mixing cold and dense filamentary gas with the diffuse, hotter wind material. As an excellent test case, we will focus on the fascinating substructures detected recently in the filament Barnard 44 (Ophiuchus) by Alves et al. Our results will provide important information on the evolution of filaments that are the fundamental building blocks of molecular clouds, especially on their intimate coupling with their turbulent and violent surrounding.