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arXiv 1409.2873astro-ph.GA
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高红移类星体宿主星系:存在恒星质量危机吗?

High-redshift quasars host galaxies: is there a stellar mass crisis?

Rosa Valiante, Raffaella Schneider, Stefania Salvadori, Simona Gallerani

摘要:

我们利用半解析层次模型GAMETE/QSOdust研究了一个5<z<6.4类星体样本的演化性质。我们发现,这些类星体的观测特性可以通过常见的形成情景很好地再现,其中恒星根据标准IMF通过静止的恒星形成和有效的合并驱动爆发形成,而中央BH通过气体吸积和BH生长-BH合并。最终,一股强烈的活动星系核驱动的风开始清除ISM中的尘埃和气体,抑制恒星的形成,并使朝向类星体的视线变得清晰。在这种情况下,所有的类星体宿主的最终恒星质量都在$(4-6)\times 10^{11} M_{sun}$范围内,比观测所允许的上限大3-30倍。我们讨论替代方案,以减轻这种明显的紧张局势:最有可能的解释驻留在大的不确定性,仍然影响在这些高z星系的动态质量测量。此外,在恒星爆发为主的阶段和活跃的类星体阶段之间的过渡,我们预测,约40%的祖星系可以被归类为亚毫米星系,虽然他们的数量迅速减少红移。

英文摘要:

We investigate the evolutionary properties of a sample of quasars at 5<z<6.4 using the semi-analytical hierarchical model GAMETE/QSOdust. We find that the observed properties of these quasars are well reproduced by a common formation scenario in which stars form according to a standard IMF, via quiescent star formation and efficient merger-driven bursts, while the central BH grows via gas accretion and BH-BH mergers. Eventually, a strong AGN driven wind starts to clear up the ISM of dust and gas, damping the star formation and un-obscuring the line of sight toward the QSO. In this scenario, all the QSOs hosts have final stellar masses in the range $(4-6)\times 10^{11} M_{sun}$, a factor 3-30 larger than the upper limits allowed by the observations. We discuss alternative scenarios to alleviate this apparent tension: the most likely explanation resides in the large uncertainties that still affect dynamical mass measurements in these high-z galaxies. In addition, during the transition between the starburst-dominated and the active QSO phase, we predict that about 40% of the progenitor galaxies can be classified as Sub Millimeter Galaxies, although their number rapidly decreases with redshift.

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