Title: A physical model for the evolving UV luminosity function of high redshift galaxies and their contribution to the cosmic reionization Show Chinese title

Title: 高红移星系的紫外光度函数演化物理模型及其对宇宙再电离的贡献

Abstract: [Abridged] We present a physical model for the evolution of the ultraviolet (UV) luminosity function (LF) of high-z galaxies taking into account in a self-consistent way their chemical evolution and the associated evolution of dust extinction. The model yields good fits of the UV and Lyman-alpha LFs at z>~2. The weak evolution of both LFs between z=2 and z=6 is explained as the combined effect of the negative evolution of the halo mass function, of the increase with redshift of the star formation efficiency, and of dust extinction. The slope of the faint end of the UV LF is found to steepen with increasing redshift, implying that low luminosity galaxies increasingly dominate the contribution to the UV background at higher and higher redshifts. The observed range of UV luminosities at high-z implies a minimum halo mass capable of hosting active star formation M_crit <~ 10^9.8 M_odot, consistent with the constraints from hydrodynamical simulations. From fits of Lyman-alpha LFs plus data on the luminosity dependence of extinction and from the measured ratios of non-ionizing UV to Lyman-continuum flux density for samples of z=~3 Lyman break galaxies and Lyman-alpha emitters, we derive a simple relationship between the escape fraction of ionizing photons and the star formation rate, impling larger escape fraction for less massive galaxies. Galaxies already represented in the UV LF (M_UV <~ -18) can keep the universe fully ionized up to z=~6, consistent with (uncertain) data pointing to a rapid drop of the ionization degree above z~6. On the other side, the electron scattering optical depth, tau_es, inferred from CMB experiments favor an ionization degree close to unity up to z=~9-10. Consistency with CMB data can be achieved if M_crit =~ 10^8.5 M_odot, implying that the UV LFs extend to M_UV =~ -13, although the corresponding tau_es is still on the low side of CMB-based estimates. Show Chinese abstract

Abstract: 我们提出了一种物理模型，用于描述高红移星系的紫外（UV）光度函数（LF）的演化，同时以自洽的方式考虑了它们的化学演化以及相关的尘埃消光演化。该模型能够很好地拟合z >~2时的UV和Lyman-alpha LF。这两个LF在z=2到z=6之间的弱演化被解释为暗晕质量函数的负演化、恒星形成效率随红移增加以及尘埃消光共同作用的结果。发现UV LF的微弱端斜率随着红移的增加而变陡，这意味着低光度星系在更高的红移处对紫外背景的贡献越来越大。高红移观测到的UV光度范围表明能够容纳活跃恒星形成的最小暗晕质量为M_crit <~ 10^9.8 M_odot，这与流体力学模拟的限制一致。 通过拟合Lyman-alpha LF加上关于消光与亮度依赖关系的数据，并测量z=~3的Lyman断层星系和Lyman-alpha发射器样本中的非电离UV与Lyman连续区通量密度比，我们推导出电离光子逃逸分数与恒星形成率之间的一个简单关系，表明较小质量的星系具有更大的逃逸分数。 UV LF中已经存在的星系（M_UV <~ -18）可以维持宇宙到z=~6时完全电离，这与指向z~6以上电离程度快速下降的数据一致（尽管这些数据存在不确定性）。另一方面，从CMB实验推断的电子散射光学深度tau_es支持到z=~9-10时电离程度接近于1。如果M_crit =~ 10^8.5 M_odot，则与CMB数据的一致性可以实现，这意味着UV LFs扩展到M_UV =~ -13，但相应的tau_es仍低于基于CMB估计的低端值。