Internal Structure of Molecular Gas in a Main-sequence Galaxy With a UV Clump at z = 1.45
Internal Structure of Molecular Gas in a Main-sequence Galaxy With a UV Clump at z = 1.45
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DOI：
10.3847/1538-4357/abdd1f
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发表时间：
2021-01
期刊：
影响因子：
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通讯作者：
Kaito Ushio;K. Ohta;F. Maeda;B. Hatsukade;K. Yabe
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作者：
Kaito Ushio;K. Ohta;F. Maeda;B. Hatsukade;K. Yabe
我们介绍了Subaru-XMM/Newton Deep Survey/UDS场对一个z = 1.45的大质量主序星星系进行的亚弧秒阿塔卡玛大型毫米/亚毫米阵列CO（2 - 1）和CO（5 - 4）观测的结果，旨在研究星系中分子气体的内部分布和性质。我们的目标星系由凸起和盘组成，在哈勃太空望远镜的图像中有一个紫外线团。CO发射谱线清晰可见，CO（5 - 4）/CO（2 - 1）通量比（R52）为1.01，与银河系相似。假设CO到H2的转换因子与金属性有关，CO（2 - 1）/CO（1 - 0）的流量比为2（银河系的值），则分子气体质量和气体质量分数（f气体=分子气体质量与分子气体质量+恒星质量的比值）分别估计为1.5 × 1011 M和0.55。我们发现，R 52峰与紫外光团的位置相一致，其值约为银河系平均值的两倍。这一结果意味着高的气体密度和/或高温的紫外线团，这定性同意的数值模拟的cluerous星系。CO（2 - 1）分布可用圆盘模型较好地描述，其半光半径为1.23kpc。与恒星分布相比，分子气体更集中在星系的中心区域。我们还发现，f气体从银河系中心的0.6下降到三倍半光半径处的0.2，表明分子气体分布在星系的中心区域，而不是恒星，似乎与凸起有关，而不是与恒星盘。
We present results of subarcsec Atacama Large Millimeter/submillimeter Array observations of CO(2–1) and CO(5–4) toward a massive main-sequence galaxy at z = 1.45 in the Subaru-XMM/Newton Deep Survey/UDS field, aiming at examining the internal distribution and properties of molecular gas in the galaxy. Our target galaxy consists of the bulge and disk, and has a UV clump in the Hubble Space Telescope images. The CO emission lines are clearly detected, and the CO(5–4)/CO(2–1) flux ratio (R 52) is ∼1, similar to that of the Milky Way. Assuming a metallicity-dependent CO-to-H2 conversion factor and a CO(2–1)/CO(1–0) flux ratio of 2 (the Milky Way value), the molecular gas mass and the gas-mass fraction (f gas = ratio of the molecular gas mass to the molecular gas mass + stellar mass) are estimated to be ∼1.5 × 1011 M ⊙ and ∼0.55, respectively. We find that R 52 peak coincides with the position of the UV clump and that its value is approximately twice higher than the galactic average. This result implies a high gas density and/or high temperature in the UV clump, which qualitatively agrees with a numerical simulation of a clumpy galaxy. The CO(2–1) distribution is well represented by a rotating-disk model, and its half-light radius is ∼2.3 kpc. Compared to the stellar distribution, the molecular gas is more concentrated in the central region of the galaxy. We also find that f gas decreases from ∼0.6 at the galactic center to ∼0.2 at three times the half-light radius, indicating that the molecular gas is distributed in the more central region of the galaxy than stars and seems to be associated with the bulge rather than with the stellar disk.