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arXiv 2005.11959astro-ph.GA
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Seyfert星系中的冷分子气体和PAH辐射

Cold molecular gas and PAH emission in Seyfert galaxies

A. Alonso-Herrero, M. Pereira-Santaella, D. Rigopoulou, I. Garcia-Bernete, S. Garcia-Burillo, A. J. Dominguez-Fernandez, F. Combes, R. I. Davies, T. Diaz-Santos… 展开作者

A. Alonso-Herrero, M. Pereira-Santaella, D. Rigopoulou, I. Garcia-Bernete, S. Garcia-Burillo, A. J. Dominguez-Fernandez, F. Combes, R. I. Davies, T. Diaz-Santos, D. Esparza-Arredondo, O. Gonzalez-Martin, A. Hernan-Caballero, E. K. S. Hicks, S. F. Hoenig, N. A. Levenson, C. Ramos Almeida, P. F. Roche, D. Rosario

摘要:

本文研究了22个邻近Seyfert星系核($\sim 24-230\,$ pc)区$11.3\,μ$ m PAH特征的探测与冷分子气体性质之间的关系。对于前者,我们使用地面(0.3-0.6”分辨率)中红外(中红外)光谱。用ALMA和NOEMA高(0.2-1.1”)角分辨率观测CO(2-1)跃迁,追踪冷分子气体。具有$11.3\,μ$ m PAH特征的核检测的Galerkin包含更多的冷分子气体(中值$1.6\times 10^7\,M_\odot$),并且在由中红外狭缝采样的区域上具有比没有检测的Galerkin更高的柱密度($N({\rm H}_2) = 2 \times 10^{23}\,{\rm cm}^{-2}$)。这表明分子气体在Seyfert核的恶劣环境中起着屏蔽PAH分子的作用。选择PAH分子萘作为例子,我们计算了暴露于2.5keV硬X射线光子时其在我们样品的核区域中的半衰期。我们估计较短的半衰期萘在没有$11.3\,μ$ m PAH检测的核比那些检测。环核尺度上的Spitzer/IRS多环芳烃比值($\sim$ 4”$\sim$ 0.25-1.3kpc)介于中性和部分电离多环芳烃的模型预测值之间。然而,在我们的样本中,具有最高核H $_2$柱密度的Seyfert星系通常并不更接近中性PAH轨道。这是因为在我们的大多数样本星系中,内部$\sim$ 4”的CO(2-1)发射并没有中心峰值,并且在一些星系中有强烈的恒星形成活动的环核位置。利用詹姆斯·韦伯太空望远镜上的MIRI中分辨率摄谱仪进行空间分辨观测,将能够区分活动星系核和恒星形成对活动星系核附近PAH发射的影响。

英文摘要:

We investigate the relation between the detection of the $11.3\,μ$m PAH feature in the nuclear ($\sim 24-230\,$pc) regions of 22 nearby Seyfert galaxies and the properties of the cold molecular gas. For the former we use ground-based (0.3-0.6" resolution) mid-infrared (mid-IR) spectroscopy. The cold molecular gas is traced by ALMA and NOEMA high (0.2-1.1") angular resolution observations of the CO(2-1) transition. Galaxies with a nuclear detection of the $11.3\,μ$m PAH feature contain more cold molecular gas (median $1.6\times 10^7\,M_\odot$) and have higher column densities ($N({\rm H}_2) = 2 \times 10^{23}\,{\rm cm}^{-2}$) over the regions sampled by the mid-IR slits than those without a detection. This suggests that molecular gas plays a role in shielding the PAH molecules in the harsh environments of Seyfert nuclei. Choosing the PAH molecule naphthalene as an illustration, we compute its half-life in the nuclear regions of our sample when exposed to 2.5keV hard X-ray photons. We estimate shorter half-lives for naphthalene in nuclei without a $11.3\,μ$m PAH detection than in those with a detection. The Spitzer/IRS PAH ratios on circumnuclear scales ($\sim$ 4" $\sim$ 0.25-1.3kpc) are in between model predictions for neutral and partly ionized PAHs. However, Seyfert galaxies in our sample with the highest nuclear H$_2$ column densities are not generally closer to the neutral PAH tracks. This is because in the majority of our sample galaxies, the CO(2-1) emission in the inner $\sim$ 4" is not centrally peaked and in some galaxies traces circumnuclear sites of strong star formation activity. Spatially resolved observations with the MIRI medium-resolution spectrograph (MRS) on the James Webb Space Telescope will be able to distinguish the effects of an active galactic nucleus (AGN) and star formation on the PAH emission in nearby AGN.

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