The observations show that less massive the galaxies are, the higher on average is their specific star formation rate (SSFR = SFR/Ms, Ms is the stellar mass). Such a trend, called the 'SSFR downsizing' (SSFR-DS) phenomenon, is seen for local and high-z (back to z~1-2) galaxy samples. We use observational data related only to disc galaxies and explore the average SSFR change with z for different masses. For Ms in the range ~10^9.5-10^10.5 Msun, the SSFR increases with (1+z) to a power that barely depends on Ms, and at all z's smaller galaxies have ever higher SSFRs. The latter strongly disagree with the LCDM hierarchical mass accretion rates. By means of self-consistent models of disc galaxy evolution inside growing LCDM halos, the effects that disc feedback-driven outflows and gas re-accretion have on the galaxy SSFR histories are explored. The parameters of the outflow and re-accretion schemes are tuned to reproduce the z~0 Mh-Ms relation inferred from observations. In the case of outflows only, the SSFR of individual model galaxies is roughly proportional to (1+z)^2.2 for all the masses with a normalization factor that depends on mass as Ms^0.1, i.e more massive galaxies have slightly larger SSFRs, contrary to the observed strong SSFR-DS trend. For the re-accretion cases, the dependence on z remains approximately the same as without re-infall, but the correlation on Ms even increases for most of the reasonable values of the model parameters. The comparison of models and observations in the SSFR-Ms plane at z~0 shows the divergent trend in SSFR as lower are the masses (upsizing vs downsizing). We explain why the models show the reported trends, and conclude that the SSFR-DS for low-mass galaxies poses a challenge for LCDM-based disc galaxy evolution models. (Abridged)
The Origin and Evolution of the Mass-Metallicity Relation using GalICS
利用GalICS（Galerkin in Cosmological Simulations）分层星系形成的半解析模型，研究了星系的不同性质，包括恒星形成率（SFR）和流出量，对星系的质量金属度关系的形状的影响，并预测了红移z=2.27和z=3.54的星系的质量金属度关系.我们的GalICS版本非常详细地实现了化学进化，并且不太依赖于瞬时循环等近似方法。我们改变模型参数控制的效率和红移依赖的SFR以及效率的超新星反馈。我们发现，控制的SFR的因素影响的关系显着在所有的红移，需要一个强大的红移依赖性，1+z成比例，以重现所观察到的关系在低质量端。事实上，在任何红移，预测的关系在高质量的一端，导致一个较差的协议与观察在这一制度。我们还发现，与外流相关的参数的变化有一个最小的影响，在高红移的关系，但在最近的过去改变其形状。因此，我们的结论是，SFR和质量之间的关系，外流是唯一重要的在塑造的关系在晚些时候。当该关系是分层的SFR很明显，预测的星系与恒星质量增加有较高的SFR，支持星系缩小的关系是起源的观点。为了重现观测到的关系，我们改变了控制恒星形成效率及其红移依赖性的参数，并将预测的关系与Erb et al.（2006）在z=2.27时和Maiolino et al.（2008）在z=3.54时进行比较，以找到最佳拟合参数。（节录）
GBT Detection of Polarization-dependent HI Absorption and HI Outflows in Local ULIRGs and Quasars
本文介绍了用罗伯特C。伯德格林班克望远镜（GBT）这些残骸是从类星体/ULIRG演化研究（QUEST）的超亮红外星系（ULIRG; L $_{8-1000 μm} > 10^{12}$ L $_\odot$）和类星体样本中选择的;我们的目标都是由活动星系核（AGN）控制的，并且是建议的ULIRG到类星体演化序列的后期阶段的样本。我们发现HI吸收（发射）的流行率是100%（29%）在ULIRG与HI检测，100%（88%）在FIR强类星体，和63%（100%）在FIR弱类星体。吸收功能与强大的中性外流，从主要驱动的恒星形成ULIRGs被驱动的类星体的活动星系核。在某些情况下，这些流出物的速度超过1500 km s $^{-1}$。出乎意料的是，我们在57%的光谱中发现了偏振相关的HI吸收（分别为88%和63%的FIR强和FIR弱类星体）。我们将这一结果归因于前景HI云对这些源的偏振连续辐射的吸收。在显示偏振光谱的类星体中，约有60%是射电强的，远高于在活动星系核中观测到的$\sim$ 10%。这种差异表明，射电喷流在塑造这些星系的环境方面起着重要作用。这些系统可能代表了一个过渡阶段，在丰富的气体合并到“成熟”的射电星系的演变。
