The luminosity gap between the two brightest members of galaxy groups and clusters is thought to offer a strong test for the models of galaxy formation and evolution. This study focuses on the statistics of the luminosity gap in galaxy groups, in particular fossil groups, e.g. large luminosity gap, in an analogy with the same in a cosmological simulation. We use spectroscopic legacy data of seventh data release (DR7) of SDSS, to extract a volume limited sample of galaxy groups utilizing modified friends-of-friends (mFoF) algorithm. Attention is paid to galaxy groups with the brightest group galaxy (BGG) more luminous than \Mr = -22. An initial sample of 620 groups in which 109 optical fossil groups, where the luminosity gap exceeds 2 magnitude, were identified. We compare the statistics of the luminosity gap in galaxy groups at low mass range from the SDSS with the same in the Millennium simulations where galaxies are modeled semi-analytically. We show that the BGGs residing in galaxy groups with large luminosity gap, i.e. fossil groups, are on average brighter and live in lower mass halos with respect to their counter parts in non-fossil systems. Although low mass galaxy groups are thought to have recently formed, we show that in galaxy groups with 15 galaxies brighter than $M_r\ge -19.5$, evolutionary process are most likely to be responsible for the large luminosity gap. We also examine a new probe of finding fossil group. In addition we extend the recently introduced observational probe based on the luminosity gap, the butterfly diagram, to galaxy groups and study the probe as a function of halo mass. This probe can, in conjunction with the luminosity function, help to fine tune the semi-analytic models of galaxies employed in the cosmological simulations.
We extend existing methods for using cross-correlations to derive redshift distributions for photometric galaxies, without using photometric redshifts. The model presented in this paper simultaneously yields highly accurate and unbiased redshift distributions and, for the first time, redshift-dependent luminosity functions, using only clustering information and the apparent magnitudes of the galaxies as input. In contrast to many existing techniques for recovering unbiased redshift distributions, the output of our method is not degenerate with the galaxy bias b(z), which is achieved by modelli…
We study the possibility of using correlations between spatial modulations in the observed luminosity distribution of galaxies and the underlying density field as a cosmological probe. Considering redshift ranges, where magnification effects due to gravitational lensing may be neglected, we argue that the dipole part of such luminosity-density correlations traces the corresponding velocity-density signal which may thus be measured from a given galaxy redshift catalogue. Assuming an SDSS-like survey with mean density $\overline{n}$ = 0.01 ($h^{-1}$ Mpc)$^{-3}$ and effective volume $V_{\rm eff}$…
Order statistics of the early-type galaxy luminosity function
我们应用顺序统计量（OS）的亮端（$M_r < -22$）的光度分布的早期型星系的光谱确定的SDSS DR 7目录。我们计算这种分布的典型OS数量的数值，测量的期望值和方差的$k^{th}$最明亮的星系在一个样本的基数$N$在一个大的合奏这样的样本。从这些统计量，我们解释了为什么和在什么限制$k^{th}$最明亮的星系可以作为标准蜡烛宇宙学研究。由于我们的样本包含所有明亮的星系，包括最亮的星系团（BCG），基于OS，我们认为，BCGs可以被认为是一个完善的Schechter光度分布的统计极值时，星系的红移，而不是集群集群。我们推测这背后的原因可能是星系团中明亮的红色椭圆星系是\em，而不是整体光度分布的随机\em样本，而是由于它们位于包含BCG的星系团中而产生偏差。我们表明，一个简单的统计玩具模型可以重现著名的BCG和第二亮星系团之间的星等差距。
We investigate the dependence of the galaxy-halo connection and galaxy density field in modified gravity models using the $N-$body simulations for $f(R)$ and nDGP models at $z=0$. Because of the screening mechanisms employed by these models, chameleon and Vainshtein, halos are clustered differently in the non-linear regime of structure formation. We quantify their deviations in the galaxy density field from the standard $Λ$CDM model under different environments. We populate galaxies in halos via the (Sub)Halo Abundance Matching. Our main results are: 1) The galaxy-halo connection {\it strongly…
2MASS/SDSS Close Major-Merger Galaxy Pairs: Luminosity Functions and Merger Mass Dependence
我们选择了一个密切的“主要合并候选人”的星系对样本，以计算的K_{s}光度函数（LF）和对分数的合并/相互作用的组成部分，在本地宇宙中的星系演化。对样本（投影间隔5 h $^{-1}$ kpc $\leq$ r $\leq$ 20 h $^{-1}$ kpc，$K_{s}$ -带星等差$Δ$ $K_{s}$ $\leq$ 1等）是通过结合2微米全天巡天（2 MASS）和斯隆数字巡天（SDSS）数据发布5（DR 5）选择的。由此产生的数据集包含340个星系，覆盖5800平方米。度一个恒星质量函数也是从LF转换而来的。微分对分数显示了星系对的比例几乎是恒定的，作为星系质量的函数，从10 $^{9}$到10 $^{11.5}$ M $_{\sun}$。由于测量的限制，差分对分数比标准的总对分数更少受到绝对幅度偏差的影响。这些结果表明，在0 $<$ z $<$ 0.1宇宙中的主要合并候选对是从$\sim$ 1.6%的星系人口发展而来的，而不依赖于星系质量的对组件低于10 $^{11}$ M $_{\sun}$。合并模型的时间尺度结合LF推导出当地合并率每单位体积的质量大于10 $^{11}$ M $_{\sun}$减少。
Environmental effects on the bright end of the galaxy luminosity function in galaxy clusters
团星系的光度函数对母星系团演化状态的依赖性仍然是一个悬而未决的问题，特别是关于最亮的团星系的形成/演化。我们计划研究一个非常不松弛的集群（“DARC”集群显示的证据，主要的，最近的合并）的样本的LF的明亮部分，并将它们与一个参考样本的松弛集群跨越可比的质量和红移范围。我们的分析是基于10个大质量X射线发光星团（0.2<z<0.3）的SDSS DR 7光度数据，始终考虑物理半径（R_200或其分数）。我们考虑r'波段的低频，并使用颜色-星等图（r'-i '，r'）来清洁我们的样本，以及考虑单独的红色和蓝色星系。我们发现，DARC和放松集群给出类似的LF参数和蓝色分数。这两个样本的亮星系BG含量不同，M_r<-22.5，因为松弛星系团的BG较少，特别是当考虑到外星系团区域0.5R_200<R<R_200时（因子2）。然而，BG中的累积光对于松弛和DARC样品是相似的。我们的结论是BG增长的亮度和减少的数量作为母星系团增长的层次结构与BG形成与其他发光星系合并。
The luminosity function of diverse satellite galaxy systems
麦克马斯特无偏星系巡天（MUGS）的高分辨率SPH星系被用来检查16个模型宿主星系的卫星系统。每个星系都有不同的质量，角动量和合并历史，产生了丰富的卫星光度函数。通过对遥远卫星系统的新观测，我们可以将这些光度函数与本星系群以外的卫星系统进行比较。我们发现，我们的模拟的光度函数比较好的观测时，光度函数根据主机质量缩放。我们使用最近发现的矮卫星和遥远卫星系统中的宿主质量之间的关系（Trentham & Tully 2009）来规范化银河系的理论完整光度函数（Koposov et al. 2008）。卫星的光度函数表示为宿主质量的函数，由dN/dM_V= 3.5 x M_host^（0.91）x 10^（0.1 x M_V-10.2）给出，其中宿主质量以M_sun为单位。宿主星系的质量可以用来预测矮卫星星系的数量，甚至当分别考虑螺旋星系和椭圆星系时，这种关系也成立。
We characterize the luminosity distribution, halo mass dependence, and redshift evolution of red galaxies in galaxy clusters using the SDSS Data Release 8 RedMaPPer cluster sample. We propose a simple prescription for the relationship between the luminosity of both central and satellite galaxies and the mass of their host halos, and show that this model is well-fit by the data. Using a larger galaxy cluster sample than previously employed in the literature, we find that the luminosities of central galaxies scale as $\langle \log L \rangle \propto A_L \log (M_{200b})$, with $A_L=0.39\pm0.04$, a…
We present a Halo Occupation Distribution (HOD) analysis of the luminosity- and colour-dependent galaxy clustering in the Sloan Digital Sky Survey. A novelty of our technique is that it uses a combination of clustering measurements in luminosity bins to perform a global likelihood analysis, simultaneously constraining the HOD parameters for a range of luminosity thresholds. We present simple, smooth fitting functions which accurately describe the resulting luminosity dependence of the best-fit HOD parameters. To minimise systematic halo modelling effects, we use theoretical halo 2-point correl…
The discovery of faint FR~I radio jets in the nearby elliptical galaxy NGC 5322 is reported here using 144 MHz LOFAR image. The jets have an angular extent of $\sim40$ arcmin or a projected physical extent of $\sim350$ kpc. The faint jets remain well collimated and disappear in the intergalactic medium, without any visible hotspot or radio lobes. The jets detected up to $\sim20$ kpc extent at higher frequencies are relatively bright within the optical extent of the galaxy but become faint abruptly outside, where detection is made only in the LOFAR image. The total radio luminosity of the galax…
We study the excess entropy and the corresponding non-gravitational feedback energy ($E_{feedback}$) in the intra-cluster medium (ICM) by considering a sample of 38 galaxy clusters using Chandra X-ray and NRAO VLA Sky Survey (NVSS)/Giant Metrewave Radio Telescope (GMRT) radio observations. We find moderate correlation of the feedback energy and brightest cluster galaxy (BCG) radio luminosity ($L_R$) with the various cluster thermal properties. We show conclusively that the active galactic nucleus (AGN) is more effective in transferring feedback energy to the ICM in less massive clusters. We fi…
Type Ia supernovae (SNe Ia) are explosions of white dwarf stars that facilitate exquisite measurements of cosmological expansion history, but improvements in accuracy and precision are hindered by observational biases. Of particular concern is the apparent difference in the corrected brightnesses of SNe Ia in different host galaxy environments. SNe Ia in more massive, passive, older environments appear brighter after having been standardized by their light-curve properties. The luminosity difference commonly takes the form of a step function. Recent works imply that environmental characteristi…
One of the most exciting advances of the current generation of telescopes has been the detection of galaxies during the epoch of reionization, using deep fields that have pushed these instruments to their limits. It is essential to optimize our analyses of these fields in order to extract as much information as possible from them. In particular, standard methods of measuring the galaxy luminosity function discard information on large-scale dark matter density fluctuations, even though this large-scale structure drives galaxy formation and reionization during the Cosmic Dawn. Measuring these de…
We derive constraints on primordial power spectrum, for the first time, from galaxy UV luminosity functions (LFs) at high redshifts. Since the galaxy LFs reflect an underlying halo mass function which depends on primordial fluctuations, one can constrain primordial power spectrum, particularly on small scales. We perform a Markov Chain Monte Carlo analysis by varying parameters for primordial power spectrum as well as those describing astrophysics. We adopt the UV LFs derived from Hubble Frontier Fields data at $z = 6 -10$, which enable us to probe primordial fluctuations on the scales of $k \…
We present the study of the dependence of galaxy clustering on luminosity and stellar mass in the redshift range 2$<$z$<$3.5 using 3236 galaxies with robust spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS). We measure the two-point real-space correlation function $w_p(r_p)$ for four volume-limited stellar mass and four luminosity, M$_{UV}$ absolute magnitude selected, sub-samples. We find that the scale dependent clustering amplitude $r_0$ significantly increases with increasing luminosity and stellar mass indicating a strong galaxy clustering dependence on these properties. Thi…
How tidal erosion has shaped the relation between globular cluster specific frequency and galaxy luminosity
我们量化到什么程度的潮汐侵蚀的球状星团（GC）所观察到的GC比频率S_N和宿主星系光度M_V之间的U形关系作出了贡献。我们使用我们的MUESLI代码计算GC生存率的典型早期类型的星系潜力，涵盖了广泛的观测到的星系属性。我们这样做的各向同性和径向各向异性GC速度分布。我们发现，在星系的半光半径范围内，GC存活分数fs与三维质量密度rho_3D的对数成线性关系，fs与（rho_3D）^（-0.17）成正比。对于一个给定的星系，生存率较低的径向各向异性配置比各向同性GC的情况下。我们将这些关系应用于Harris et al.（2013）的219个早型星系的文献样本，M_V=[-24.5：-15.5] ma。预期GC存活分数范围从最大半径的最大质量星系的~50%到最紧凑星系的~10%。我们发现中等光度星系M_V=[-20.5：-17.5]等具有最强的GC侵蚀。在所考虑的文献样本中，预测的GC存活分数因此与M_V定义了u形关系，类似于比频率S_N和M_V之间的关系。因此，当针对GC侵蚀的影响校正S_N值时，S_N与M_V的u形几乎完全被消除。我们的结论是，潮汐侵蚀是一个重要的贡献者GC比频率和宿主星系光度之间的U形关系。当从对附近宇宙GC系统的观测中推断原始恒星团簇形成效率时，必须考虑到这一点。
Ultimate age-dating method for galaxy groups; clues from the Millennium Simulations
有许多研究致力于鉴定化石星系群，可以说是形成时代相对较老的星系群。大多数这样的研究确定化石群，主要是基于一个大的光度差距，这是两个最明亮的星系之间的星等差距。在千禧年宇宙学模拟中对这些类型星系群的研究表明，虽然它们已经积累了相当大一部分质量，相对来说比光度差距小的星系群要早，但这个参数本身并不能有效地完全区分“老”和“年轻”星系群，这是一个基于晕质量积累历史的标签。我们研究了Guo et al.（2011）基于Millennium Simulation的半解析模型中的星系。我们建立了一组四个观测可测量的参数，可以结合使用，以确定一个子集的星系群是老的，具有很高的概率。因此，我们认为，基于光度差距选择的化石群样本将导致旧星系群样本的污染。通过对最亮星系的光度及其与星系群光度质心的偏移量进行限制，我们可以大大改善年龄测定。
The astronomy community has at its disposal a large back catalog of public spectroscopic galaxy redshift surveys that can be used for the measurement of luminosity functions. Utilizing the back catalog with new photometric surveys to maximum efficiency requires modeling the color selection bias imposed on selection of target galaxies by flux limits at multiple wavelengths. The likelihood derived herein can address, in principle, all possible color selection biases through the use of a generalization of the luminosity function, $Φ(L)$, over the space of all spectra: the spectro-luminosity funct…
