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arXiv 1609.08792astro-ph.GA
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Lyman连续泄漏早型星系光谱合成研究中的半经验AGN探测阈值

Semi-empirical AGN detection threshold in spectral synthesis studies of Lyman-continuum-leaking early-type galaxies

Leandro S. M. Cardoso, Jean Michel Gomes, Polychronis Papaderos

摘要:

各种证据表明,早期类型星系(ETG)的大部分核心实际上是疏散的温暖电离气体。这意味着假设的活动星系核(AGN)产生的莱曼连续谱(LyC)辐射可以从这些系统的核中逃逸出来,而不会被局部再处理成星云发射,这将阻止它们作为塞弗特星系的可靠光谱分类标准诊断发射线比。这些ETG的光谱能量分布(SED)将缺乏星云辐射,基本上由古老的恒星成分和来自活动星系核的无特征的幂律(PL)连续体组成。在这种情况下出现的一个问题是,活动星系核的组成部分是否可以检测到目前的光谱人口合成的光学,具体来说,这些技术是否有效地放置活动星系核的检测阈值在LyC泄漏星系。为了定量地解决这个问题,我们采取了一种综合的方法,涉及光谱拟合与星光合成SED组成的恒星发射的特点是一个10 Gyr老ETG和活动星系核的幂律分量,贡献了一小部分$0\leq x_{\mathrm{AGN}} < 1$的单色光度在$λ_0=$ 4020。除了PL分布$F_ν \propto ν^{-α}$与规范$α=1.5$的一组拟合外,我们还使用了多个PL与$0.5 \leq α\leq 2$的基础,用于信噪比为5- $10^3$的合成SED网格。我们的分析表明,一个有效的活动星系核检测阈值在$x_{\mathrm{AGN}}\simeq 0.26$,这表明,相当一部分的ETG托管显着的吸积动力的核活动可能是失踪的活动星系核的人口统计。

英文摘要:

Various lines of evidence suggest that the cores of a large portion of early-type galaxies (ETGs) are virtually evacuated of warm ionised gas. This implies that the Lyman-continuum (LyC) radiation produced by an assumed active galactic nucleus (AGN) can escape from the nuclei of these systems without being locally reprocessed into nebular emission, which would prevent their reliable spectroscopic classification as Seyfert galaxies with standard diagnostic emission-line ratios. The spectral energy distribution (SED) of these ETGs would then lack nebular emission and be essentially composed of an old stellar component and the featureless power-law (PL) continuum from the AGN. A question that arises in this context is whether the AGN component can be detected with current spectral population synthesis in the optical, specifically, whether these techniques effectively place an AGN detection threshold in LyC-leaking galaxies. To quantitatively address this question, we took a combined approach that involves spectral fitting with STARLIGHT of synthetic SEDs composed of stellar emission that characterises a 10 Gyr old ETG and an AGN power-law component that contributes a fraction $0\leq x_{\mathrm{AGN}} < 1$ of the monochromatic luminosity at $λ_0=$ 4020 Å. In addition to a set of fits for PL distributions $F_ν \propto ν^{-α}$ with the canonical $α=1.5$, we used a base of multiple PLs with $0.5 \leq α\leq 2$ for a grid of synthetic SEDs with a signal-to-noise ratio of 5-$10^3$. Our analysis indicates an effective AGN detection threshold at $x_{\mathrm{AGN}}\simeq 0.26$, which suggests that a considerable fraction of ETGs hosting significant accretion-powered nuclear activity may be missing in the AGN demographics.

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