尘埃

• 消光曲线
• 发射线的消光可能和连续谱的消光不同
• Halpha/Hbeta 线比

内禀数值：2.86（恒星形成），3.1（AGN） 参见Osterbrock & Ferland 2006

• 尘埃的红外发射: dustEM
• 尘埃与气体有关，气体的光深可以从low-ionization interstellar (IS) absorption lines(e.g., Si II, O I, Fe II)获得 (Shapley et al. 2003)

e.g. If the two Si II transitions at 1260 and 1527A are optically thin, then the ratio of their equivalent widths will be W1260/W1527 > 6. The observed ratio is W1260/W1527 ~ 1, implying that the lines are saturated and hence their depths are sensitive to the covering fraction of Si II-enriched material.

对于比912A更短的波长来说，气体的吸收消光是最主要的而不是dust，但是气体和尘埃是相关的，参见[1]