The effect of large‐scale power on simulated spectra of the Lyα forest
The effect of large‐scale power on simulated spectra of the Lyα forest
复制标题
大功率功率对 Lyα 森林模拟光谱的影响
DOI：
--
复制
发表时间：
2007
期刊：
影响因子：
--
通讯作者：
T. Jena
中科院分区：
文献类型：
--
作者：
D. Tytler;P. Paschos;D. Kirkman;M. Norman;T. Jena
我们探讨的影响，我们使用的模拟星系际介质（IGM）在红移2的盒子的大小。我们研究模拟的流体动力学代码enzo，不同的只是在盒子的大小。我们研究了冷暗物质（CDM）的分布和Lyα森林吸收的许多统计数据。较大的盒子具有较少的具有显著吸收（通量<0.96）的像素，在较长的拉伸中具有较少或没有吸收的更多像素，并且它们具有较宽的Lyα线。较大的盒子不同，只是因为它们包括来自较长波长模式的功率。这些模式导致更高的峰值密度、更高的速度和更热的气体。与大型模拟相比，小型模拟太冷了。当我们故意增加输入IGM的热量时，我们可以在两倍大小的模拟中近似Lyα森林。
当我们将盒子的大小加倍时，大多数统计数据与我们最大的76.8 Mpc盒子中的值的差异大约减少了2倍。当盒子从38.4 Mpc扩大到76.8 Mpc时，平均Lyα吸收减少0.5%，我们遇到不同的常见CDM密度的频率改变2%，典型的Lyα线宽，通量值的频率和通量的功率谱都改变4- 7%，柱密度分布的变化高达15%。一个76.8 Mpc的盒子足够大，误差为1017 cm-2。将晶胞尺寸从75 kpc减小到18.75 kpc，使得在log NH i < 14 cm−2时差异更大，并且对于更高的柱没有帮助。在一个有18.75 kpc单元的非常大的盒子中，模拟光谱中的Lyα线会宽2.6 km s−1。模拟的Lyα森林在小尺度上有20%的功率太小，在大尺度上有50%的功率太小。一个大得多的盒子只会增加几个百分点的大尺度功率。我们证实了Kim等人（2007）和博尔顿等人（2008）的发现，模拟光谱也有不同的通量分布比数据。
很难看出我们使用流行的宇宙学和天体物理学参数进行的光学薄模拟如何与z= 2时的Lyα森林数据相匹配。增加辐射传输效应，特别是架屏蔽将降低高过密度下的温度，可能改善与线宽的匹配，并且它将有助于匹配高列密度线的数量。我们还可以用更软的电离光谱来减小线宽，或者使用σ8 > 0.9，这具有增加大尺度功率的额外好处。
We explore the effects of size of the box that we use for simulations of the intergalactic medium (IGM) at redshift 2. We examine simulations from the hydrodynamic code enzo that differ only in box size. We study the cold dark matter (CDM) distribution and many statistics of the Lyα forest absorption from the IGM. Larger boxes have fewer pixels with significant absorption (flux <0.96), more pixels in longer stretches with little or no absorption, and they have wider Lyα lines. The larger boxes differ only because they include power from longer wavelength modes. These modes result in higher peak densities, higher velocities and hotter gas. Small simulations are too cold compared to larger ones. When we deliberately increase the heat we put into the IGM, we can approximate the Lyα forest in a simulation of twice the size.
When we double the box size, the difference of most statistics from their value in our largest 76.8 Mpc box is reduced by approximately a factor of 2. When we enlarge the box from 38.4 to 76.8 Mpc, the mean Lyα absorption decreases 0.5 per cent, the frequency with which we encounter different common CDM densities changes by 2 per cent, typical Lyα linewidths, the frequency of flux values and the power spectrum of the flux all change by 4–7 per cent, and the column density distribution changes by up to 15 per cent. A 76.8 Mpc box is large enough to give errors of 1017 cm−2. Decreasing the cell size from 75 to 18.75 kpc makes the difference larger at log NH i < 14 cm−2, and does not help with the higher columns. The Lyα lines in the simulated spectra from a very large box with 18.75 kpc cells would be too wide by 2.6 km s−1. The simulated Lyα forest has 20 per cent too little power on small scales and 50 per cent too little large scales. A much larger box would increase the large-scale power only a few per cent. We confirm the Kim et al. (2007) and Bolton et al. (2008) finding that the simulated spectra also have different flux distributions than data.
It is hard to see how our optically thin simulations using popular cosmological and astrophysical parameters can match the Lyα forest data at z= 2. Adding radiation transfer effects, especially shelf-shielding will reduce the temperature at high overdensities, possibly improving the match to linewidths, and it will help match the number of high column density lines. We could also decrease the linewidths with a softer ionizing spectrum, or by using σ8 > 0.9, which has the additional benefit of increasing the large-scale power.
关于高红移类星体周围 H II 区域的大小
DOI：
10.1111/j.1745-3933.2007.00283.x
发表时间：
2007
期刊：
Proceedings of the International Astronomical Union
影响因子：
--
作者：
Maselli A;Gallerani S;Ferrara A;Choudhury T. R.
通讯作者：
Choudhury T. R.