在星系形成模型中，我们研究了特定恒星形成率（SSFR）及其在$z\gtsim 4$的演化，其中恒星形成是由冷吸积流驱动的。我们发现，恒定的恒星形成和反馈效率不能再现观测到的SSFR与恒星质量的趋势和观测到的$z>4$缺乏演化。模型星系与$\log(M_*) \ltsim 9.5$ M $_{\odot}$显示系统性较低的特定恒星形成率的数量级，而大质量星系与M $_* \gtsim 5 \times 10^{10}$ M $_{\odot}$有高达一个数量级较大的SSFR相比，斯塔克等人最近的观测。为了恢复这些观测结果，我们应用经验恒星形成效率的星系，规模与主机晕速度色散为$\propto 1/σ^3$在星系合并。我们发现，这种修改需要随机性重现的意见，即只适用于合并过程中，而不是吸积驱动的恒星形成阶段。我们的选择在合并过程中的恒星形成效率，使我们能够捕捉到这两个，在低质量的恒星形成和淬火在高质量，并在同一时间产生一个恒定的SSFR恒星质量关系在$z\gtsim 4$的假设下，大多数观察到的星系是在合并引发的恒星形成阶段。我们的研究结果表明，所观察到的高z低质量星系与高SSFR可能是经常相互作用的系统，经历了爆发的恒星形成率和效率（模式1），在低红移$z \ltsim 3$星系，这是冷吸积调节的恒星形成系统与较低的恒星形成效率（模式2）。
英文摘要：
We study the specific star formation rate (SSFR) and its evolution at $z\gtsim 4$, in models of galaxy formation, where the star formation is driven by cold accretion flows. We show that constant star formation and feedback efficiencies cannot reproduce the observed trend of SSFR with stellar mass and its observed lack of evolution at $z>4$. Model galaxies with $\log(M_*) \ltsim 9.5$ M$_{\odot}$ show systematically lower specific star formation rates by orders of magnitudes, while massive galaxies with M$_* \gtsim 5 \times 10^{10}$ M$_{\odot}$ have up to an order of magnitude larger SSFRs, compared to recent observations by Stark et al.. To recover these observations we apply an empirical star formation efficiency in galaxies that scales with the host halo velocity dispersion as $\propto 1/σ^3$ during galaxy mergers. We find that this modification needs to be of stochastic nature to reproduce the observations, i.e. only applied during mergers and not during accretion driven star formation phases. Our choice of star formation efficiency during mergers allows us to capture both, the boost in star formation at low masses and the quenching at high masses, and at the same time produce a constant SSFR-stellar mass relation at $z\gtsim 4$ under the assumption that most of the observed galaxies are in a merger triggered star formation phase. Our results suggest that observed high-z low mass galaxies with high SSFRs are likely to be frequently interacting systems, which experienced bursts in their star formation rate and efficiency (mode 1), in contrast to low redshift $z \ltsim 3$ galaxies which are cold accretion-regulated star forming systems with lower star formation efficiencies (mode 2).
We first present a catalogue of photometric redshifts for 14.68 million galaxies derived from the 7-band photometric data of Hyper Suprime-Cam Subaru Strategic Program and the Wide-field Infrared Survey Explorer using the nearest-neighbour algorithm. The redshift uncertainty is about 0.024 for galaxies of z<0.7, and steadily increases with redshift to about 0.11 at z~2. From such a large data set, we identify 21,661 clusters of galaxies, among which 5537 clusters have redshifts z>1 and 642 clusters have z>1.5, significantly enlarging the high redshift sample of galaxy clusters. Cluster richnes…
Anomaly detection for machine learning redshifts applied to SDSS galaxies
我们提出了一个机器学习红移估计的异常检测分析。异常检测允许删除不良的训练样本，这可能会对红移估计产生不利影响。异常的训练例子可能是光谱红移不正确的光度星系，或者一个或多个光度测量不好的星系。我们选择了250万个“干净”的SDSS DR 12星系与可靠的光谱红移，和6730个“异常”星系与光谱红移测量标记为不可靠的。我们污染的干净的基础星系样本与星系的不可靠的红移，并试图恢复污染星系使用椭圆包络技术。然后，我们训练四个机器学习架构，用于对污染样本和预处理的“去除异常”样本进行红移分析，并在没有任何预处理的情况下生成的干净验证样本上测量红移统计。我们发现，与对所探索的每个机器学习例程的污染样本进行训练相比，在异常移除样本上进行训练时，所有测量统计数据的改善高达80%。我们进一步描述了一种估计基础数据样本的污染分数的方法。
Low-Redshift Ly-alpha Selected Galaxies from GALEX Spectroscopy: A Comparison with Both UV-Continuum Selected Galaxies and High-Redshift Ly-alpha Emitters
The spin of late-type galaxies at redshifts z < 1.2
利用大天文台起源深空巡天（GOODS）观测的高红移星系数据，研究了星系自旋的演化。通过简单的动力学考虑，我们估计的自旋盘星系在我们的样本，并发现其分布是一致的，发现附近的星系。定义一个无量纲的角动量参数的星系盘组件（$λ_{d}$），我们没有发现的红移范围内的演化迹象$0.4 \leq z \leq 1.2$。我们发现，我们的高红移星系的自旋的质量和环境的依赖性是类似的低$z$星系，表现出强烈的依赖于质量，在这个意义上说，低质量的系统呈现出更高的$λ_{d}$值比高质量的星系，没有显着的依赖于环境的密度。这些结果使我们得出结论，虽然个别盘星系可能偶尔遭受强烈的演变，他们的演变方式，银河系人口的整体自旋分布保持不变，从$z\sim1$到现在的时代。
Precision-era optical cluster cosmology calls for a precise definition of the red sequence (RS), consistent across redshift. To this end, we present the Red Dragon algorithm: an error-corrected multivariate Gaussian mixture model (GMM). Simultaneous use of multiple colors and smooth evolution of GMM parameters result in a continuous RS and blue cloud (BC) characterization across redshift, avoiding the discontinuities of red fraction inherent in swapping RS selection colors. Based on a mid-redshift spectroscopic sample of SDSS galaxies, a RS defined by Red Dragon selects quenched galaxies (low …
The redshift distribution of galactic-scale lensing systems provides a laboratory to probe the velocity dispersion function (VDF) of early-type galaxies (ETGs) and measure the evolution of early-type galaxies at redshift z ~ 1. Through the statistical analysis of the currently largest sample of early-type galaxy gravitational lenses, we conclude that the VDF inferred solely from strong lensing systems is well consistent with the measurements of SDSS DR5 data in the local universe. In particular, our results strongly indicate a decline in the number density of lenses by a factor of two and a 20…
