亮红外星系NGC 1614中多谱线示踪的致密分子气体

利用高空间分辨率的¹²CO(1-0)、¹³CO(1-0)、¹²CO(3-2)、¹²CO(6-5)、HCN(3-2)、\lk HCN(4-3)、 HCO⁺(3-2)和HCO⁺(4-3)分子谱线的ALMA (Atacama Large Millimeter/ submillimeter Array)归档数据, 来研究近邻亮红外星系NGC 1614的分子气体性质, 尤其是致密分子气体的性质. 在高分辨率分子气体谱线的积分强度图中, 在星系中心区域($<$ 1kpc)可以看到环状结构, 分子气体主要分布于星系中心区域, 核区分子气体含量较少. ¹²CO(1-0)显示出向南部、 北部以及东南部的延展结构, 高阶的CO ($J \ge$ 3, J为转振能级量子数)分子谱线和致密分子HCN、HCO⁺谱线显示, 较致密的分子气体主要集中于星系中心区域. HCN(4-3)/¹²CO(1-0)和HCN⁺(4-3)/¹²CO(1-0)积分强度比值图显示, 致密分子气体主要集中于中心区域的环状结构上. HCN/HCO⁺强度比值的分布变化表明星暴环的不同区域可能具有不同的激发条件. HCN/HCO⁺(4-3)强度比值分布在环的东、西部(sim0.44 pm 0.04)高于环的南、北部(sim0.35 pm 0.03). HCN/HCO⁺(3-2)强度比值较高的区域(sim0.38 pm 0.04)分布在HCN(3-2)峰值位置, 而环的西北、东南部强度比值相对较低(sim0.3 pm 0.03). 对于中心不同区域 HCN/HCO⁺比值变化的原因进行了讨论.

The Dense Molecular Gas in the Luminous Infrared Galaxy NGC 1614

We investigate the molecular gas properties, especially the dense molecular gas in NGC 1614, using the ALMA (Atacama Large Millimeter/submillimeter Array) high resolution archival data of ¹²CO(1-0), ¹³CO(1-0), ¹²CO(3-2), ¹²CO(6-5), HCN(3-2), HCO⁺(3-2), HCN(4-3), and HCO⁺(4-3). From the high-resolution integrated intensity maps, a ring structure was detected in the central region ($<$ 1kpc), and the molecular gas mainly distributes in the central region while there is little gas in the nucleus. The ¹²CO(1-0) shows an extended structure to the south, north, and southeast, and CO ($J \ge 3$, J is the quantum number of rotational vibration levels), HCN and HCO⁺ show that the dense gas mainly concentrated in the central region. Similarly, HCN(4-3)/¹²CO(1-0) and HCO⁺(4-3)/¹²CO(1-0) ratio maps show that the dense molecular gas is mainly concentrated in the ring in the central region. The HCN/HCO⁺ ratios, show that the different regions of the starburst ring might have different excitation conditions.\lk The variations of HCN/HCO⁺ values in different region of central region may be due to the gas density and temperature. For HCN/HCO⁺(4-3) ratio map, the higher intensity values (sim0.44 pm 0.04) were obtained in the eastern and western region of the ring, compared to the northern and southern region (sim0.35 pm 0.03). For HCN/HCO⁺(3-2) ratio map, the higher values (sim0.38 pm 0.04) are distributed at peak location of HCN(3-2) emission, while the lower values (sim0.3 pm 0.03) are distributed at the northwestern and southeastern region of the ring. The mechanism of variations of HCN/HCO⁺ values in the central region of the galaxy has been discussed in the article.