早期恒星形成星系的亚毫米亮度
Sub-millimeter brightness of early star-forming galaxies
摘要：
基于一个早期恒星形成星系的三维模型，我们探讨了亚毫米亮度的演化。模型星系来自Mori & Umemura对一个原始星系的超高分辨率化学动力学模拟，其中在t <0.3 Gyr时SFR为~10 Msun/yr，在t> 0.3 Gyr时为几Msun/yr。前者很好地再现了所观察到的LAEs和LBG的性质，后者。我们求解了该模型星系中尘埃星际介质的三维辐射转移，考虑了尘埃颗粒的尺寸分布，并计算了尘埃温度随星系演化时间的变化。我们发现星际介质的团簇性对亚毫米亮度起着重要的作用。在LAE阶段，尘埃颗粒集中在遍布银河系的星团恒星形成区域，这些颗粒可以有效地吸收来自恒星的紫外辐射。结果，尘埃被加热到T> 35 K。在LBG阶段，连续的超新星将尘埃颗粒驱离恒星形成区域。然后，这些颗粒就不能吸收太多来自恒星的辐射，并变成接近CMB温度的冷态。因此，尘埃温度随演化时间的延长而降低，在t = 0.1 Gyr和t = 1.0 Gyr时，尘埃的质量加权平均温度分别为T = 26 K和T = 21 K。通过这种分析，结果表明，亚毫米亮度是在LAE阶段比在LBG阶段，虽然灰尘与气体的比例单调增加作为时间的函数。我们通过将模型星系放置在给定的红移处来推导光谱能量分布。当模型星系位于δ> z> 2时，在850 μ m处的峰值通量为S_850~0.2 - 0.9 mJy。这意味着ALMA可以用16个天线在不到一小时的时间内探测到SFR为10 Msun/yr的早期恒星形成星系。
英文摘要：
Based on a three-dimensional model of an early star-forming galaxy, we explore the evolution of the sub-millimeter brightness. The model galaxy is employed from an ultra-high-resolution chemodynamic simulation of a primordial galaxy by Mori & Umemura, where the SFR is ~ 10 Msun/yr at t<0.3 Gyr and several Msun/yr at t>0.3 Gyr. The former phase well reproduces the observed properties of LAEs and the latter does LBGs. We solve the three-dimensional radiative transfer in the clumpy interstellar media in this model galaxy, taking the size distributions of dust grains into account, and calculate the dust temperature as a function of galactic evolutionary time. We find that the clumpiness of interstellar media plays an important role for the sub-millimeter brightness. In the LAE phase, dust grains are concentrated on clumpy star-forming regions that are distributed all over the galaxy, and the grains can effectively absorb UV radiation from stars. As a result, the dust is heated up to T>35 K. In the LBG phase, the continuous supernovae drive dust grains far away from star-forming regions. Then, the grains cannot absorb much radiation from stars, and becomes into a cold state close to the CMB temperature. Consequently, the dust temperature decreases with the evolutionary time, where the mass-weighted mean temperature is T=26 K at t=0.1 Gyr and T=21 K at t=1.0 Gyr. By this analysis, it turns out that the sub-millimeter brightness is higher in the LAE phase than that in the LBG phase, although the dust-to-gas ratio increases monotonically as a function of time. We derive the spectral energy distributions by placing the model galaxy at a given redshift. The peak flux at 850 micron is found to be S_850 ~ 0.2 - 0.9 mJy if the model galaxy is placed at 6>z>2. This means that ALMA can detect an early star-forming galaxy with SFR of ~ 10 Msun/yr by less than one hour integration with 16 antennas.
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