附近的星系细丝和Lya森林：对抗模拟和观测的UV背景
Nearby galaxy filaments and the Lya forest: confronting simulations and the UV background with observations
摘要：
模拟形成的大尺度结构预测，暗物质，低密度的高度电离的气体，和星系形成10 - 40兆秒差距规模的细丝。这些结构在星系的分布中很容易识别，但在气体的分布中还没有直接观察到。我们利用24活动星系核的Ly-alpha吸收线，提出了一种新的探测这些细丝的方法。我们使用了一个新的邻近星系（cz<10，000 km/s）的目录，在这里分析的空间区域中，完整的光度约为0.05 L*。利用24个活动星系核的HST谱，我们在cz~3500 km/s对30 × 5 Mpc的星系丝气体进行了取样。我们所有的视线都在任何已知的丝状星系的维里半径之外。在灯丝轴的500 kpc内，检测率约为80%，而在灯丝的2.1 Mpc以上没有检测到。Lya线的宽度与长丝碰撞参量相关，并且我们的样品中的四个BLA都发生在长丝轴的400 kpc内，表明温度和/或湍流增加。与模拟相比，我们发现最近的Haardt & Madau（2012）河外电离背景预测电离光子少了3-5倍。使用更强的辐射场与灯丝轴2.1 Mpc内的氢密度分布相匹配，但模拟仍然高估了距离轴2.1和5 Mpc之间的检测率。
英文摘要：
Simulations of the formation of large-scale structure predict that dark matter, low density highly ionized gas, and galaxies form 10 40 Mpc scale filaments. These structure are easily recognized in the distribution of galaxies, but have not been directly observed in the distribution of the gas. We use Ly-alpha absorption lines in the spectra of 24 AGN to present a new way to probe these filaments. We use a new catalogue of nearby (cz<10,000 km/s) galaxies, complete down to a luminosity of about 0.05 L* for the region of space analyzed here. Using HST spectra of 24 AGN we sample the gas associated with a 30x5 Mpc galaxy filament at cz~3500 km/s. All of our sightlines pass outside the virial radius of any known filament galaxy. Within 500 kpc of the filament axis the detection rate is ~80%, while no detections are seen more than 2.1 Mpc from the filament. The width of the Lya lines correlates with filament impact parameter and the four BLAs in our sample all occur within 400 kpc of the filament axis, indicating increased temperature and/or turbulence. Comparing to simulations, we find that the recent Haardt & Madau (2012) extragalactic ionizing background predicts a factor 3-5 too few ionizing photons. Using a more intense radiation field matches the hydrogen density profile within 2.1 Mpc of the filament axis, but the simulations still overpredict the detection rate between 2.1 and 5 Mpc from the axis.
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