塌缩纤维的热演化和化学演化
Thermal and Chemical Evolution of Collapsing Filaments
摘要：
星系际细丝构成了将星系连接在一起的宇宙网的基础，并为星系的生长和吸积提供了重要的气体储存库。在这里，我们提出了非常高分辨率的二维模拟的热和化学演变的这种细丝，利用32种化学网络，跟踪从氢，氧和碳形成的关键分子的演变。我们研究了在很宽的参数范围内，包括初始密度，初始温度，强度的离解紫外线背景，和金属的细丝的演变。在低红移的$Z \approx 0.1 Z_\odot $细丝中，演化完全由初始冷却时间决定。如果这足够短，细丝的中心总是塌陷，形成含有大量分子的致密冷核。在高红移的$Z=10^{-3} Z_\odot$纤维中，坍缩进行得慢得多。这主要是由于较低的初始温度，这导致在达到原子冷却极限之前密度的增加要温和得多，使得随后的分子冷却效率低得多。最后，我们研究了附近矮星系的引力势如何影响暗条的坍缩，并将其与NGC 5253进行了比较，NGC 5253是一个附近的恒星爆发矮星系，被认为是由暗条气体的吸积提供燃料。与我们的基准情况相反，在电势的中心形成了大量的密度峰。由于化学物质形成和冷却发生的速率增加，该峰比灯丝的其余部分发展得更快。我们发现，我们实现了与NGC 5253相似的吸积率，但我们的二维模拟没有恢复射电观测中看到的巨大分子云的形成。
英文摘要：
Intergalactic filaments form the foundation of the cosmic web that connect galaxies together, and provide an important reservoir of gas for galaxy growth and accretion. Here we present very high resolution two-dimensional simulations of the thermal and chemical evolution of such filaments, making use of a 32 species chemistry network that tracks the evolution of key molecules formed from hydrogen, oxygen, and carbon. We study the evolution of filaments over a wide range of parameters including the initial density, initial temperature, strength of the dissociating UV background, and metallicity. In low-redshift, $Z \approx 0.1 Z_\odot $ filaments, the evolution is determined completely by the initial cooling time. If this is sufficiently short, the center of the filament always collapses to form dense, cold core containing a substantial fraction of molecules. In high-redshift, $Z=10^{-3} Z_\odot$ filaments, the collapse proceeds much more slowly. This is due mostly to the lower initial temperatures, which leads to a much more modest increase in density before the atomic cooling limit is reached, making subsequent molecular cooling much less efficient. Finally, we study how the gravitational potential from a nearby dwarf galaxy affects the collapse of the filament and compare this to NGC 5253, a nearby starbusting dwarf galaxy thought to be fueled by the accretion of filament gas. In contrast to our fiducial case, a substantial density peak forms at the center of the potential. This peak evolves faster than the rest of the filament due to the increased rate at which chemical species form and cooling occur. We find that we achieve similar accretion rates as NGC 5253 but our two-dimensional simulations do not recover the formation of the giant molecular clouds that are seen in radio observations.
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