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arXiv 0907.3491astro-ph.CO
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z ~ 0.5亮2型类星体的宿主星系

Host Galaxies of Luminous Type 2 Quasars at z ~ 0.5

Xin Liu, Nadia L. Zakamska, Jenny E. Greene, Michael A. Strauss, Julian H. Krolik, Timothy M. Heckman

摘要:

我们提出了深双子座GMOS光谱的九个发光类星体的红移z ~ 0.5,从SDSS 2型类星体样品。我们选择的目标具有高的本征亮度(M_V < -26 mag),如[O III] 5007 A发射线亮度(L_[O III])所示。我们的样本有一个中值黑洞质量为~ 10^8.8 M_sun,假设局部M_BH-σ_* 关系和中值爱丁顿比为~ 0.7,使用G波段测量的恒星速度色散σ_*。我们根据宽H-β的强度估算了散射类星体光对恒星连续谱的污染,并提供了污染随L_[O III]变化的经验标定;对于L_[O III] = 10^9.5 L_sun的天体,散射光的比例约为L_5100的30%。星族合成表明,年轻的星暴后星族(< 0.1 Gyr)在发光的2型类星体中很普遍,除了相对较老的星族(> 1 Gyr)主导恒星质量之外。He II 4686 A周围的宽发射复合物的亮度高达10^8.3 L_sun,在9个靶中的3个中被明确检测到,表明沃尔夫-拉叶布居。人口综合表明,~ 500万年后的星爆人口贡献显着的亮度(> 50%的L_5100)的所有三个对象与沃尔夫-拉叶检测。我们发现了两个具有双核的天体和四个具有密切伴星的天体。我们的结果可能表明,发光的2型类星体跟踪星系相互作用的早期阶段,可能负责类星体和星暴活动。

英文摘要:

We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at redshifts z ~ 0.5, drawn from the SDSS type 2 quasar sample. Our targets were selected to have high intrinsic luminosities (M_V < -26 mag) as indicated by the [O III] 5007 A emission-line luminosity (L_[O III]). Our sample has a median black hole mass of ~ 10^8.8 M_sun inferred assuming the local M_BH-sigma_* relation and a median Eddington ratio of ~ 0.7, using stellar velocity dispersions sigma_* measured from the G band. We estimate the contamination of the stellar continuum from scattered quasar light based on the strength of broad H-beta, and provide an empirical calibration of the contamination as a function of L_[O III]; the scattered light fraction is ~ 30% of L_5100 for objects with L_[O III] = 10^9.5 L_sun. Population synthesis indicates that young post-starburst populations (< 0.1 Gyr) are prevalent in luminous type 2 quasars, in addition to a relatively old population (> 1 Gyr) which dominates the stellar mass. Broad emission complexes around He II 4686 A with luminosities up to 10^8.3 L_sun are unambiguously detected in three out of the nine targets, indicative of Wolf-Rayet populations. Population synthesis shows that ~ 5-Myr post-starburst populations contribute substantially to the luminosities (> 50% of L_5100) of all three objects with Wolf-Rayet detections. We find two objects with double cores and four with close companions. Our results may suggest that luminous type 2 quasars trace an early stage of galaxy interaction, perhaps responsible for both the quasar and the starburst activity.

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