Mid-infrared properties of nearby low-luminosity AGN at high angular resolution
Mid-infrared properties of nearby low-luminosity AGN at high angular resolution
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DOI：
10.1051/0004-6361/201116693
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发表时间：
2011-09
影响因子：
6.5
通讯作者：
D. Asmus;D. Asmus;P. Gandhi;A. Smette;S. Hönig;W. Duschl;W. Duschl
中科院分区：
文献类型：
--
作者：
D. Asmus;D. Asmus;P. Gandhi;A. Smette;S. Hönig;W. Duschl;W. Duschl
利用VLT/VISIR对低光度活动星系核（LLAGN）进行了高空间分辨率的中红外（MIR）12 μm连续成像。我们的目标是确定LLAGN的核MIR辐射是否与活动星系核统一模型的关键组成部分--尘埃遮蔽环的存在相一致。基于现有的硬X射线光度和先前已知的硬X射线和12 μm光度之间的紧密相关性，我们选择了17个附近的LLAGN样本，而没有可用的VISIR N波段测光。结合档案VISIR数据的9个额外的LLAGN与可用的X射线测量，数据集代表了大部分的南部LLAGN目前可从地面上的和平号。在17个观测到的LLAGN中，检测到7个，而上限是针对10个未检测到的。这使VLT/VISIR探测到的活动星系核总数增加到50个以上。除了NGC 3125外，所有的探测器在空间尺度上都是点状的。探测结果与已知的MIR-X射线相关性没有明显的偏差，但在亮度<10 41 erg/s时超过了1/10，散射范围很窄（σ = 0.35 dex，斯皮尔曼秩ρ = 0.92）。后者主要是由X射线光度的不确定性。有趣的是，在局部星暴星系中也发现了类似的相关性，其斜率相当，但归一化值相差2.6个数量级。此外，我们比较了VISIR数据与斯皮策/IRS和IRAS的低空间分辨率数据。通过使用定标的星爆模板光谱能量分布和多环芳烃（PAH）11.3 μm发射线，我们能够将75%的LLAGN的VISIR测光的最大核成星污染限制在30%。它们是NGC 1097和NGC 1566，可能具有未解析的强PAH排放。此外，在不确定度范围内，MIRX射线的光度比在吸积率超过4个数量级时不变。这些结果是一致的存在的尘埃环面在所有观察到的LLAGN，虽然喷流或吸积盘作为起源的MIR发射不能被排除。最后，由于MIR-X射线相关性对所有LLAGN和Seyfert都成立，这是一个非常有用的经验工具，可以在这些核的MIR和X射线功率之间进行转换。
We present high spatial resolution mid-infrared (MIR) 12 μm continuum imaging of low-luminosity active galactic nuclei (LLAGN) obtained with VLT/VISIR. Our goal is to determine whether the nuclear MIR emission of LLAGN is consistent with the existence of a dusty obscuring torus, the key component of the unification model for AGN. Based on available hard X-ray luminosities and the previously known tight correlation between the hard X-ray and 12 μm luminosities, we selected a sample of 17 nearby LLAGN without available VISIR N-band photometry. Combined with archival VISIR data of 9 additional LLAGN with available X-ray measurements, the dataset represents the bulk of southern LLAGN currently detectable from the ground in the MIR. Of the 17 observed LLAGN, 7 are detected, while upper limits are derived for the 10 non-detections. This increases the total number of AGN detected with VLT/VISIR to more than 50. All detections except NGC 3125 appear point-like on a spatial scale of ∼0.35 �� . The detections do not significantly deviate from the known MIR-X-ray correlation but exceed it by a factor of ∼10 down to luminosities <10 41 erg/s with a narrow scatter (σ = 0.35 dex, Spearman rank ρ = 0.92). The latter is dominated by the uncertainties in the X-ray luminosity. Interestingly, a similar correlation with a comparable slope but with a normalization differing by ∼2.6 orders of magnitude has been found for local starburst galaxies. In addition, we compared the VISIR data with lower spatial resolution data from Spitzer/IRS and IRAS. By using a scaled starburst template spectral energy distribution and the polycyclic aromatic hydrocarbon (PAH) 11.3 μm emission line, we were able to restrict the maximum nuclear star-formation contamination of the VISIR photometry to 30% for 75% of the LLAGN. Exceptions are NGC 1097 and NGC 1566, which may possess unresolved strong PAH emission. Furthermore, the MIRX-ray luminosity ratio is unchanged over more than 4 orders of magnitude in accretion rate within the uncertainties. These results are consistent with the existence of the dusty torus in all observed LLAGN, although a jet or accretion disk as origin of the MIR emission cannot be excluded. Finally, because the MIR-X-ray correlation holds for all LLAGN and Seyferts, this is a very useful empirical tool for converting between the MIR and X-ray powers of these nuclei.