作为尘埃颗粒凝聚实验室的亚毫米波星系
Submillimetre galaxies as laboratories for dust grain coagulation
AI总结：
本研究将亚毫米波星系作为尘埃颗粒凝聚的实验室，结合观测数据与湍流模型分析颗粒生长尺寸，发现凝聚过程存在速度阈值，颗粒仅能生长至微米级，证明亚毫米波星系可用于约束尘埃凝聚相关物理过程。
摘要：
致密星际介质（ISM）中的凝聚过程是决定最大尘埃颗粒尺寸的重要过程。我们将亚毫米波星系（SMGs）用作颗粒凝聚的实验室，因为在已知的各类星系族群中，部分亚毫米波星系拥有星系尺度下最致密的星际介质。我们基于从亚毫米波星系观测到的典型尘埃质量密度估算出的星际介质平均密度，研究了此类致密环境中尘埃颗粒的最大生长尺寸。我们还结合强恒星反馈预期会产生的超声速湍流模型，考虑了局部密度增强的情况。在无限制凝聚模型（即不设置任何凝聚阈值速度的模型）中，若湍流的马赫数$\u2112\gtrsim 3$，则在观测估算的平均气体密度下可形成尺寸约为$30~\mu$m的大颗粒。但我们排除了这种可能性，因为远红外（FIR）波段观测到的发射率指数$\beta\simeq 2$表明，此类大颗粒无法在亚毫米波星系中大量形成。这意味着凝聚过程并非不受限制地进行：30微米颗粒的速度应当大于凝聚阈值速度。若我们采用一项理论研究给出的凝聚阈值（上限）颗粒速度（约0.08 km s$^{-1}$），则颗粒很可能仅能生长至微米级别，该尺寸足够小，不会对远红外发射率指数产生影响。上述结果表明，亚毫米波星系可用于约束与尘埃凝聚相关的物理过程。
英文摘要：
Coagulation in the dense interstellar medium (ISM) is an important process that determines the size of the largest grains. We use submillimetre galaxies (SMGs) as laboratories of grain coagulation, since some of them host the densest ISM on a galactic scale among various populations of galaxies known. We examine how large the grains can be in such dense environments based on the mean ISM density estimated from the observed typical dust mass density in SMGs. We also consider local density enhancement based on a model of supersonic turbulence, which is expected from strong stellar feedback. In the unlimited coagulation model, in which we do not impose any coagulation threshold velocity, grains as large as $\sim 30~μ$m can form under the observationally estimated mean gas density if the Mach number of turbulence is $\mathcal{M}\gtrsim 3$. We exclude this possibility since the observed emissivity index $β\simeq 2$ in the far infrared (FIR) indicates that such large grains cannot actively form in SMGs. This means that coagulation does not proceed in an unlimited way: 30-$μ$m grains should have velocities larger than the coagulation threshold. If we use a coagulation threshold (upper limit) grain velocity ($\sim 0.08$ km s$^{-1}$) taken from a theoretical study, grains likely grow only up to $μ$m size, which is small enough not to affect the FIR emissivity index. The above results indicate that SMGs can be used to constrain the physical processes relevant to coagulation.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
