标题： 早期星系中的电离气体：对Mgb及其他恒星光谱线指数的影响 显示英文标题

标题： Ionized gas in early-type galaxies: Its effect on Mgb and other stellar line-strength indices

摘要： 鉴于最近发现星云发射线在早期类型星系的内部区域普遍存在，我们评估了它们对恒星光吸收线指数的影响。 我们推导出了解析表达式，用于描述由星云发射线存在引起的原子和分子吸收线指数的变化。 我们发现，位于5199 Å的[N I]发射线双线对Mgb线强度测量有显著影响。 对于具有星云发射特征的早期类型星系核区常见的[N I]双线典型等效宽度，Mgb指数人为增强0.4至2 Å，这占早期类型星系中Mgb线典型等效宽度的很大一部分。 我们在NGC 2974的情况下展示了这种效应。 显示英文摘要

摘要： In the light of the recent finding that nebular emission lines are commonly found in the inner regions of early-type galaxies, we evaluate their effect to stellar absorption-line indices. We derive analytical expressions for changes induced by the presence of nebular emission lines, both for atomic and molecular absorption-line indices. We find that the [NI] emission-line doublet at 5199 A can significantly affect Mgb line-strength measurements. For typical equivalent widths of the [NI] doublet in nuclei of early-type galaxies featuring nebular emission, the Mgb index is artificially enhanced by 0.4 - 2 A, which represents a significant fraction of the typical equivalent width of the Mgb line in early-type galaxies. We illustrate this effect in the case of NGC 2974.