NGC 4278中心的多相含尘气体
Multi-Phase Dusty Gas in the Center of NGC 4278
摘要：
利用红外光谱仪对椭圆LINER星系NGC 4278的中心kpc区域进行了Spitzer光谱成像观测。这些观测揭示了扩展电离气体、热分子氢和尘埃的丰富中红外发射特征。气体和尘埃的不同相态密切相关，属于同一个细长特征。我们进一步研究了多相尘埃气体的性质，以揭示电离和激发的潜在机制。中心区PAH谱带比和强度特征可能反映了选择性破坏导致的粒径分布改变。H $_{2}$ S（0）-S（7）纯转动谱线与光子解离区（PDR）相比，具有较高的激发温度和较高的强度。探测到一条强而长的[SiIII]发射线，这可能是星际尘埃中硅耗尽减少的迹象。我们还发现了与H $_{2}$ S（1）发射增强有关的扩展的高电离区。我们的结论是，需要一个冲击加热组件来解释所观察到的发射特性，这可能是由云-云的相互作用过程中吸积冷气体从大HI盘触发。
英文摘要：
We present the Spitzer spectroscopic mapping observations toward the central kpc region of the nearby elliptical LINER galaxy, NGC 4278, by using the Infrared Spectrograph (IRS). These observations reveal rich mid-IR emission features of extended ionized gas, warm molecular hydrogen and dust. Different phases of gas and dust are closely related and belong to a same elongated feature. We further study properties of multi-phase dusty gas to uncover the underlying mechanism of ionization and excitation. The band ratio and intensity of PAH features in the central region might reflect modified size distribution resulted from selective destruction. H$_{2}$ S(0)-S(7) pure rotational lines of molecular hydrogen show excessive intensity and moderately high excitation temperature comparing with photon dissociation region (PDR). A strong and extended [SiII] emission line is detected, which could be a sign of reduced depletion of silicon in interstellar dust. We also discover an extended high ionization region associated with enhanced H$_{2}$ S(1) emission. We conclude that a shock-heating component is required to account for observed emission characteristics, which could be triggered by cloud-cloud interactions during accretion of cold gas from the large HI disk.
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