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arXiv 2009.05049astro-ph.GA
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早期星系星际介质中的速度色散

Velocity dispersion in the interstellar medium of early galaxies

M. Kohandel, A. Pallottini, A. Ferrara, S. Carniani, S. Gallerani, L. Vallini, A. Zanella, C. Behrens

摘要:

利用[CII] $158μ\rm{m}$谱线研究了再电离时期(EoR)星系的空间分辨视向速度色散结构。我们的实验室是一个模拟的原型莱曼break星系,“小苍兰”,SERRA套件的一部分。分析包括红移范围6 < z < 8,当小苍兰处于非常活跃的组装阶段时。我们使用[CII]高光谱数据立方体为三个动态不同的演化阶段(z=7.4的螺旋盘,z=8.0的合并和z=6.5的扰动盘)构建速度色散图。在0.005”($\simeq 30 pc$)的高空间分辨率下,观测到的光度加权平均速度色散为$σ_{\rm{CII}}$ ~23-38 km/s,最大值属于高结构扰动盘阶段。低分辨率的观测往往会高估$σ_{\rm CII}$值,这是由于光束拖尾效应取决于特定的星系结构。对于0.02”(0.1”)的角分辨率,平均速度色散比实际速度色散大16-34%(52-115%)。小苍兰星系中的[CII]发射气体的Toomre参数$\mathcal{Q}$ ~0.2,旋转色散比$v_{\rm c}/σ$ ~ 7,与z=2-3星系中观测到的相似。速度色散的主要能量来源是引力过程,例如合并/吸积事件;来自恒星反馈的能量输入通常是次主导的(< 10%)。最后,我们发现,解决$σ_{\rm{CII}} - Σ_{\rm SFR}$关系是相对平坦的$0.02<Σ_{\rm SFR}/{{\rm M}_{\odot}} \mathrm{yr}^{-1} {\mathrm kpc}^{-2} < 30$,与大多数数据躺在派生的分析关系$σ\propto Σ_{\rm SFR}^{5/7}$。在高SFR时,来自恒星反馈的贡献的增加使关系变陡,并且$σ_{\rm{CII}}$略微上升。

英文摘要:

We study the structure of spatially resolved, line-of-sight velocity dispersion for galaxies in the Epoch of Reionization (EoR) traced by [CII] $158μ\rm{m}$ line emission. Our laboratory is a simulated prototypical Lyman-break galaxy, "Freesia", part of the SERRA suite. The analysis encompasses the redshift range 6 < z < 8, when Freesia is in a very active assembling phase. We build velocity dispersion maps for three dynamically distinct evolutionary stages (Spiral Disk at z=7.4, Merger at z=8.0, and Disturbed Disk at z=6.5) using [CII] hyperspectral data cubes. We find that, at a high spatial resolution of 0.005" ($\simeq 30 pc$), the luminosity-weighted average velocity dispersion is $σ_{\rm{CII}}$~23-38 km/s with the highest value belonging to the highly-structured Disturbed Disk stage. Low resolution observations tend to overestimate $σ_{\rm CII}$ values due to beam smearing effects that depend on the specific galaxy structure. For an angular resolution of 0.02" (0.1"), the average velocity dispersion is 16-34% (52-115%) larger than the actual one. The [CII] emitting gas in Freesia has a Toomre parameter $\mathcal{Q}$~0.2 and a rotational-to-dispersion ratio of $v_{\rm c}/σ$~ 7 similar to that observed in z=2-3 galaxies. The primary energy source for the velocity dispersion is due to gravitational processes, such as merging/accretion events; energy input from stellar feedback is generally subdominant (< 10%). Finally, we find that the resolved $σ_{\rm{CII}} - Σ_{\rm SFR}$ relation is relatively flat for $0.02<Σ_{\rm SFR}/{{\rm M}_{\odot}} \mathrm{yr}^{-1} {\mathrm kpc}^{-2} < 30$, with the majority of data lying on the derived analytical relation $σ\propto Σ_{\rm SFR}^{5/7}$. At high SFR, the increased contribution from stellar feedback steepens the relation, and $σ_{\rm{CII}}$ rises slightly.

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