基于ALMA高分辨率的多谱线数据对NGC 1068核区中物理性质的研究  

Physical Properties of the Nuclear Region of NGC 1068 Based on ALMA High-resolution Multi-spectral Lines

作　　者：林淑婷 高煜 谈清华 LIN Shu-ting;GAO Yu;TAN Qing-hua(Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing 210023;School of Astronomy and Space Science,University of Science and Technology of China,Hefei 230026;Department of Astronomy,College of Physical Science and Technology,Xiamen University,Xiamen 361005)

机构地区：[1]中国科学院紫金山天文台,南京210023 [2]中国科学技术大学天文与空间科学学院,合肥230026 [3]厦门大学物理科学与技术学院天文学系,厦门361005

出　　处：《天文学报》2023年第2期54-71,共18页Acta Astronomica Sinica

基　　金：国家自然科学基金项目(11803090、11861131007、12033004、11520101002、12003070);国家重点研发计划(2017YFA 0402704);中国科学院前沿科学重点研究计划(QYZDJ-SSW-SLH008)资助。

摘　　要：利用ALMA干涉阵望远镜(Atacama Large Millimeter/submillimeter Array)的高分辨(~0.2′′-0.7′′)的多谱线数据,包括CO(1-0)、CO(2-1)、CO(3-2)、HCN(1-0)、HCO^(+)(1-0)、HCN(3-2)、HCO^(+)(3-2)、HCN(4-3)和HCO^(+)(4-3),并结合连续谱数据对近邻星系NGC 1068核区的物理性质进行了研究.速度积分强度图显示核周盘(CircumNuclear Disk,CND)呈现不对称的环状结构,尺度~300 pc.各分子谱线均显示,CND上的东发射结(E-knot)比西发射结(W-knot)有着更强的发射,且E-knot处表现出的分子气体的速度比W-knot更高.致密分子气体含量占比(用HCN或HCO^(+)不同转动跃迁线与CO(1-0)的积分强度比值表示),以及致密分子气体比值(HCN/HCO^(+))均在CND的东部表现出更高的值,意味着CND东部和西部有着不同的物理环境或化学组成.CO(3-2)/CO(1-0)的积分强度比值在E-knot很高,意味着该处极端的物理环境导致分子激发增强.通过与单镜望远镜JCMT(James Clerk Maxwell Telescope)比较HCN(4-3)和HCO^(+)(4-3)的流量,得到高分辨率ALMA成图测量的致密分子气体在1 kpc尺度上的流量损失为10%~20%.各分子谱线在E-knot和W-knot的流量比为1.8~3.9,CND中E-knot和W-knot的差异可能与活动星系核(Active Galactic Nucleus,AGN)的反馈有关.此外,在AGN位置处的CO(2-1)、CO(1-0)和HCO^(+)(1-0)的谱线发现了吸收特征.这种吸收主要为其背景的强连续谱辐射导致,同时AGN附近的气体下落也可能产生自吸收现象.Using the multi-spectral lines from ALMA(Atacama Large Millimeter/submillimeter Array)with high-resolution(∼0.2′′–0.7′′)and the continuum data,this work studies the physical properties of the nuclear region of nearby galaxy NGC 1068.The spectral lines include CO(1-0),CO(2-1),CO(3-2),HCN(1-0),HCO^(+)(1-0),HCN(3-2),HCO^(+)(3-2),HCN(4-3)and HCO^(+)(4-3).The CND(CircumNuclear Disk)shows an asymmetric ring structure with a size of∼300 pc in the velocity-integrated intensity images.All the molecular lines of the CND show stronger emission at the eastern knot(E-knot)than the western knot(W-knot)of the CND.Furthermore,the E-knot shows larger velocities than the W-knot,which indicates that there is significant rotational pattern in the CND.The dense gas fraction(traced by the different transitions of HCN or HCO^(+)to CO(1-0)integrated intensity ratios)and dense gas ratio(HCN/HCO^(+))are higher at the E-knot,implying that the E-and W-knots have different physical environments or chemical compositions.The HCN emission in the CND show enhancement compared with HCO^(+),which could be affected by the AGN(Active Galactic Nucleus)radiation and starburst activity.The CO(3-2)/CO(1-0)integrated intensity ratio is a significant indicator of gas excitation.CO(3-2)/CO(1-0)ratios show much higher values at the E-knot,suggesting that there is molecular excitation enhancement caused by the extreme physical environment.Compared with the fluxes of HCN(4-3)and HCO^(+)(4-3)from the singledish telescope JCMT(James Clerk Maxwell Telescope),the ALMA missing fluxes of dense molecular gas on 1 kpc scale are about 10%–20%.The spectral lines show that the flux ratios between E-knot and W-knot are∼1.8–3.9.These differences shown between E-knot and W-knot may be associated with the AGN feedback.In addition,the CO(2-1),CO(1-0)and HCO^(+)(1-0)spectra show absorption features in the position of AGN.This absorption could be caused by the strong background of continuum emissions,and the gas inflow around the AGN can produce self-absorp

关 键 词：恒星:形成 亚毫米:星际介质 星系:星暴 射电谱线:星系 星系:个别:NGC 1068 

分 类 号：P157[天文地球—天文学]