Mid-infrared spectral evidence for a luminous dust enshrouded source in Arp 220
Mid-infrared spectral evidence for a luminous dust enshrouded source in Arp 220
复制标题
Arp 220 中发光尘埃笼罩源的中红外光谱证据
DOI：
10.1051/0004-6361:20031656
复制
发表时间：
2003
影响因子：
6.5
通讯作者：
Jacqueline V. Keane
中科院分区：
文献类型：
--
作者：
H. Spoon;A. Moorwood;D. Lutz;A. Tielens;R. Siebenmorgen;Jacqueline V. Keane
我们重新分析了超亮红外星系阿普220的6-12微米ISO光谱，得出的结论是，它与典型星暴的放大版本不一致。相反，两个与星系NGC 4418和M 83光谱的模板拟合以及与尘埃模型的拟合都表明，它最好由典型的星暴成分和大量吸收的尘埃连续体的组合来表示，前者表现出PAH发射特征，后者贡献了6-12 µm通量的约40%，并可能主导了光度。相对于先前对阿普220的研究，特别重要的是，7.7 µm处的发射特征包括PAH发射和由冰和硅酸盐吸收产生的更广泛的成分，而不是严重吸收的连续谱。然而，对PAH排放源的消光似乎相对较低。我们将PAH发射和大量灰尘/冰吸收的成分与Soifer等人（2002年）在其更高空间分辨率10 µm研究中分别确定的扩散发射区和两个致密核联系起来。吸收连续谱与嵌入的银河系原恒星的相似性以及尘埃模型的结果都意味着，阿普220中嵌入的源可能是由星暴活动提供动力的，尽管密度极高。由于活动星系核的高度消光，根据现有的数据，不可能排除活动星系核也贡献了部分或全部观测到的光度。然而，在这种情况下，测量其硬X射线发射的上限将要求阿普220是已知的最高度模糊的活动星系核。
We have re-analyzed the 6-12 µm ISO spectrum of the ultra-luminous infrared galaxy Arp 220 with the conclusion that it is not consistent with that of a scaled up version of a typical starburst. Instead, both template fitting with spectra of the galaxies NGC 4418 and M 83 and with dust models suggest that it is best represented by combinations of a typical starburst component, exhibiting PAH emission features, and a heavily absorbed dust continuum which contributes ∼40% of the 6-12 µm flux and likely dominates the luminosity. Of particular significance relative to previous studies of Arp 220 is the fact that the emission feature at 7.7 µm comprises both PAH emission and a broader component resulting from ice and silicate absorption against a heavily absorbed continuum. Extinction to the PAH emitting source, however, appears to be relatively low. We ten- tatively associate the PAH emitting and heavily dust/ice absorbed components with the diffuse emission region and the two compact nuclei respectively identified by Soifer et al. (2002) in their higher spatial resolution 10 µm study. Both the similarity of the absorbed continuum with that of the embedded Galactic protostars and results of the dust models imply that the embedded source(s) in Arp 220 could be powered by, albeit extremely dense, starburst activity. Due to the high extinction, it is not possible with the available data to exclude that AGN(s) also contribute some or all of the observed luminosity. In this case, however, the upper limit measured for its hard X-ray emission would require Arp 220 to be the most highly obscured AGN known.