A detailed study of the radio-FIR correlation in NGC 6946 with Herschel-PACS/SPIRE from KINGFISH
A detailed study of the radio-FIR correlation in NGC 6946 with Herschel-PACS/SPIRE from KINGFISH
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DOI：
10.1051/0004-6361/201220249
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发表时间：
2013-01
影响因子：
6.5
通讯作者：
F. Tabatabaei;E. Schinnerer;E. Murphy;R. Beck;B. Groves;S. Meidt;M. Krause;H. Rix;K. Sandstrom;A. Crocker;M. Galametz;G. Helou;C. Wilson;R. Kennicutt;D. Calzetti;B. Draine;G. Aniano;D. Dale;G. Dumas;C. Engelbracht;C. Engelbracht;K. D. Gordon;J. Hinz;K. Kreckel;E. Montiel;H. Roussel
中科院分区：
文献类型：
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作者：
F. Tabatabaei;E. Schinnerer;E. Murphy;R. Beck;B. Groves;S. Meidt;M. Krause;H. Rix;K. Sandstrom;A. Crocker;M. Galametz;G. Helou;C. Wilson;R. Kennicutt;D. Calzetti;B. Draine;G. Aniano;D. Dale;G. Dumas;C. Engelbracht;C. Engelbracht;K. D. Gordon;J. Hinz;K. Kreckel;E. Montiel;H. Roussel
我们推导出 NGC 6946 上同步加速器光谱指数的分布，并使用 KINGFISH Herschel-PACS 和 SPIRE 数据研究射电连续谱（同步加速器）和远红外 (FIR) 发射之间的相关性。研究了射电-FIR 相关性作为恒星形成速率、磁场强度、辐射场强度和总气体表面密度的函数。同步加速器发射遵循恒星形成区域和臂间区域中存在的所谓磁臂。同步加速器谱指数沿着磁臂最陡（α_n ~ 1），而在巨 Hii 区域和星系中心的地方则平坦（α_n ~ 0.6−0.7）。 α_n 图为在星系盘中传播的宇宙射线电子（CRE）的老化和能量损失提供了观测证据。整个星系同步加速器-远红外相关性的变化被证明是恒星形成和磁场强度的函数。我们发现，当漫射星际辐射场是尘埃的主要热源时，同步加速器发射与冷尘埃发射的相关性比与暖尘埃发射的相关性更好。同步加速器-FIR 相关性表明磁场与气体密度之间存在耦合。 NGC 6946 显示总（湍流）磁场强度 B 与恒星形成速率表面密度 Σ_(SFR) 之间的幂律行为，指数为 0.14 (0.16) ± 0.01。这表明在活跃的恒星形成区域中，随着气体湍流的增加，湍流磁场的有效产生。此外，表明B-Σ_(SFR)幂律指数对于正常星系中的湍流场和总场是相似的。另一方面，对于与星团环境相互作用的星系，湍流磁场的该指数比总磁场的指数更陡。同步加速器-FIR相关性的逐尺度分析表明，ISM影响旧/扩散CRE的传播，导致2.2 GeV CRE的扩散系数为D_0 = 4.6 × 10^(28) cm^2 s^(-1)。
We derive the distribution of the synchrotron spectral index across NGC 6946 and investigate the correlation between the radio continuum (synchrotron) and far-infrared (FIR) emission using the KINGFISH Herschel-PACS and SPIRE data. The radio-FIR correlation is studied as a function of star formation rate, magnetic field strength, radiation field strength, and the total gas surface density. The synchrotron emission follows both star-forming regions and the so-called magnetic arms present in the inter-arm regions. The synchrotron spectral index is steepest along the magnetic arms (α_n ~ 1), while it is flat in places of giant Hii regions and in the center of the galaxy (α_n ~ 0.6−0.7). The map of α_n provides observational evidence for aging and energy loss of cosmic ray electrons (CREs) propagating in the disk of the galaxy. Variations in the synchrotron-FIR correlation across the galaxy are shown to be a function of both star formation and magnetic field strength. We find that the synchrotron emission correlates better with cold rather than with warm dust emission, when the diffuse interstellar radiation field is the main heating source of dust. The synchrotron-FIR correlation suggests a coupling between the magnetic field and the gas density. NGC 6946 shows a power-law behavior between the total (turbulent) magnetic field strength B and the star formation rate surface density Σ_(SFR) with an index of 0.14 (0.16) ± 0.01. This indicates an efficient production of the turbulent magnetic field with the increasing gas turbulence expected in actively star forming regions. Moreover, it is suggested that the B-Σ_(SFR) power law index is similar for the turbulent and the total fields in normal galaxies. On the other hand, for galaxies interacting with the cluster environment this index is steeper for turbulent magnetic fields than it is for the total magnetic fields. The scale-by-scale analysis of the synchrotron-FIR correlation indicates that the ISM affects the propagation of old/diffused CREs, resulting in a diffusion coefficient of D_0 = 4.6 × 10^(28) cm^2 s^(-1) for 2.2 GeV CREs.