A 2–3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946
A 2–3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946
复制标题
对附近螺旋星系 NGC 6946 中心进行的 2 × 3 毫米高分辨率分子线勘测
DOI：
10.1051/0004-6361/202142624
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发表时间：
2022
影响因子：
6.5
通讯作者：
Puschnig, J.
中科院分区：
文献类型：
--
作者：
Eibensteiner, C.;Barnes, A. T.;Bigiel, F.;Schinnerer, E.;Liu, D.;Meier, D. S.;Usero, A.;Leroy, A. K.;Rosolowsky, E.;Puschnig, J.
星系中心复杂的物理、运动学和化学特性使它们成为利用分子线发射进行检查的有趣环境。我们提出了新的 2 − 4" (∼75 − 150 pc at 7.7 Mpc) 2 和 3 mm 观测结果，覆盖了附近双棒螺旋星系 NGC 6946 的中心 50" (∼1.9 kpc)，这是用 IRAM Plateau de Bure 干涉仪获得的。我们检测十种分子的谱线：CO、HCN、HCO+、HNC、CS、HC3N、N2H+、C2H、CH3OH 和 H2CO。我们用已发表的 1 mm CO 观测和 33 GHz 连续谱观测对这些进行了补充，以探索 150 pc 尺度上的恒星形成速率表面密度 ΣSFR。在本文中，我们分析了与 NGC 6946 内棒相关的区域——核区 (NUC)、北部 (NBE) 和南部内棒末端 (SBE)，并重点关注短间距校正体积 (CO) 和稠密气体示踪剂（HCN、HCO+ 和 HNC）。我们发现 HCO+ 与 ΣSFR 相关性最好，但稠密气体分数 (fdense) 和稠密气体的恒星形成效率 (SFEdense) 拟合显示出与大规模圆盘观测预期不同的行为。 SBE 比 NBE 具有更高的 ΣSFR、fdense 和冲击气体分数。我们检查线路比率诊断并发现 NBE 的 CO(2−1)/CO(1−0) 比率高于 NUC。此外，与现有河外数据集的比较表明，使用 HCN/HNC 比率来探测动力学温度并不适合河外地区的千秒差距和亚千秒差距尺度。最后，我们的研究表明，HCO+/HCN 比率可能不是诊断星系中活动星系核活动的唯一指标。
The complex physical, kinematic, and chemical properties of galaxy centres make them interesting environments to examine with molecular line emission. We present new 2 − 4″ (∼75 − 150 pc at 7.7 Mpc) observations at 2 and 3 mm covering the central 50″ (∼1.9 kpc) of the nearby double-barred spiral galaxy NGC 6946 obtained with the IRAM Plateau de Bure Interferometer. We detect spectral lines from ten molecules: CO, HCN, HCO+, HNC, CS, HC3N, N2H+, C2H, CH3OH, and H2CO. We complemented these with published 1 mm CO observations and 33 GHz continuum observations to explore the star formation rate surface density ΣSFRon 150 pc scales. In this paper, we analyse regions associated with the inner bar of NGC 6946 – the nuclear region (NUC), the northern (NBE), and southern inner bar end (SBE) and we focus on short-spacing corrected bulk (CO) and dense gas tracers (HCN, HCO+, and HNC). We find that HCO+correlates best with ΣSFR, but the dense gas fraction (fdense) and star formation efficiency of the dense gas (SFEdense) fits show different behaviours than expected from large-scale disc observations. The SBE has a higher ΣSFR,fdense, and shocked gas fraction than the NBE. We examine line ratio diagnostics and find a higher CO(2−1)/CO(1−0) ratio towards NBE than for the NUC. Moreover, comparison with existing extragalactic datasets suggests that using the HCN/HNC ratio to probe kinetic temperatures is not suitable on kiloparsec and sub-kiloparsec scales in extragalactic regions. Lastly, our study shows that the HCO+/HCN ratio might not be a unique indicator to diagnose AGN activity in galaxies.