z=4.5亚毫米星系中的分子气体：大爆炸后10亿年大合并的证据
Molecular Gas in a Submillimeter Galaxy at z=4.5: Evidence for a Major Merger at 1 Billion Years after the Big Bang
摘要：
本文报道了利用IRAM Plateau de Bure干涉仪（PdBI）和NRAO甚大阵（VLA）对Z=4.5毫米探测星系COSMOS_J100054+023436（以下简称J100+0234）中CO分子谱线发射的探测。用PdBI观测到的CO（4-3）谱线全线宽约为1000 km/s，积分线通量为0.66 Jy km/s，CO光度为3.2e10 L_sun。与VLA探测到的CO（2-1）谱线发射的3.3sigma比较表明，分子气体可能热化到J=4-3跃迁能级。相应的气体分子质量为2.6e10 M_sun，假设一个ULIRG类似的转换因子。从空间偏移的红色和蓝移线峰值和线宽的动态质量为1.1e11 M_太阳的估计假设合并的情况下。分子气体分布与物体的静止坐标系光学和无线电位置一致，同时与先前检测到的Ly $α$发射偏移0.5“。J1000+0234表现出非常典型的低红移（z~2）亚毫米星系（SMG）的性质，因此很可能是这一星群中长期以来被寻找的高红移（z>4）天体之一。大的CO（4-3）谱线宽度与其高度扰动的静止坐标系紫外几何一起表明，在大爆炸后大约10亿年，一个正在进行的大合并。考虑到它的大恒星形成率（SFR）>1000 M_sun/yr和分子气体含量，这个物体可能是在z=2的红移处观察到的“红死”椭圆的前兆。
英文摘要：
We report the detection of CO molecular line emission in the z=4.5 millimeter-detected galaxy COSMOS_J100054+023436 (hereafter: J100+0234) using the IRAM Plateau de Bure interferometer (PdBI) and NRAO's Very Large Array (VLA). The CO(4-3) line as observed with PdBI has a full line width of ~1000 km/s, an integrated line flux of 0.66 Jy km/s, and a CO luminosity of 3.2e10 L_sun. Comparison to the 3.3sigma detection of the CO(2-1) line emission with the VLA suggests that the molecular gas is likely thermalized to the J=4-3 transition level. The corresponding molecular gas mass is 2.6e10 M_sun assuming an ULIRG-like conversion factor. From the spatial offset of the red- and blue-shifted line peaks and the line width a dynamical mass of 1.1e11 M_sun is estimated assuming a merging scenario. The molecular gas distribution coincides with the rest-frame optical and radio position of the object while being offset by 0.5'' from the previously detected Ly$α$ emission. J1000+0234 exhibits very typical properties for lower redshift (z~2) sub-millimeter galaxies (SMGs) and thus is very likely one of the long sought after high redshift (z>4) objects of this population. The large CO(4-3) line width taken together with its highly disturbed rest-frame UV geometry suggest an ongoing major merger about a billion years after the Big Bang. Given its large star formation rate (SFR) of >1000 M_sun/yr and molecular gas content this object could be the precursor of a 'red-and-dead' elliptical observed at a redshift of z=2.
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