星系际氦的完全再电离是IGM历史上的一个重大事件,He II Gunn-Peterson槽的紫外观测使我们能够描述这一过程在z~3处的结束。由于中间的氢吸收,类星体允许这样的研究是罕见的,只有33个已知的文献中,其中大多数是最近发现的。我们扩展了我们以前的发现工作,并提出了13个新的He II类星体,其红移为2.82 < z < 3.77,这里选择的效率约为80%,其中包括几个比以前已知的绝大多数要亮得多的类星体。这是均匀观测到的He II类星体的最大样本,覆盖了如此宽的红移范围,它们显示出IGM不透明度随红移增加的证据,正如氦再电离时期所预期的那样。在单个或平均光谱中没有看到He II Lyα类星体发射的证据,这给宽线区域的标准模型带来了问题。目前的快速进展,在研究He II类星体已经大大促进了宇宙起源光谱仪的HST,我们讨论的仪器和其他微妙的,必须考虑到IGM He II观测。
英文摘要:
The full reionization of intergalactic helium was a major event in the history of the IGM, and UV observations of the He II Gunn-Peterson trough allow us to characterize the end of this process at z~3. Due to intervening hydrogen absorption, quasars allowing such study are rare, with only 33 known in the literature, and most of those are very recent discoveries. We expand on our previous discovery work, and present 13 new He II quasars with redshifts 2.82 < z < 3.77, here selected with ~80% efficiency, and including several that are much brighter than the vast majority of those previously known. This is the largest sample of uniformly observed He II quasars covering such a broad redshift range, and they show evidence of IGM opacity increasing with redshift, as expected for the helium reionization epoch. No evidence of He II Lyα quasar emission is seen in individual or averaged spectra, posing a problem for standard models of the broad line region. The current rapid advance in the study of He II quasars has been greatly facilitated by the Cosmic Origins Spectrograph on HST, and we discuss the instrumental and other subtleties that must be taken into account in IGM He II observations.
Direct Observation of Cosmic Strings via their Strong Gravitational Lensing Effect: II. Results from the HST/ACS Image Archive
我们已经搜索了4.5平方度的HST/ACS档案图像,寻找宇宙弦,识别出相似的、微弱的星系对,并选择了那些排列与引力透镜一致的星系群。我们在五次大面积的HST财政调查(覆盖总面积为2.22平方度)中没有发现宇宙弦的证据,或者在346张多过滤器的客座观察者图像(1.18平方度)中没有发现宇宙弦的证据。假设模拟精确地预测了宇宙中宇宙弦的数量,这种未探测到的情况使我们能够在95%的置信水平下(在每种情况下,相对于另一个参数,边缘化)将无单位的普适宇宙弦张力的上限定为G μ/c^2 < 2.3 x 10^-6,宇宙弦密度的上限定为Omega_s < 2.1 x 10^-5。我们在318张单过滤器访客观测者图像(1.08平方度)中发现了四个可疑的宇宙弦候选者,我们无法用现有数据最终消除它们。这些候选者中的任何一个被确认为宇宙弦都意味着G μ/c^2 ~ 10^-6和Ω_s ~ 10^-5。然而,我们估计至少有92%的机会,这些字符串候选人是随机排列的星系。如果我们假设这些候选者确实是错误的检测,那么我们对G μ/c^2和Ω_s的最终限制将降到6.5 x 10^-7和7.3 x 10^-6。由于HST/ACS图像存档的天空覆盖范围很广,因此上述限制是通用的。它们对搜索的字段数量非常敏感,并且可以使用即将到来的HST数据进一步减少两倍以上。
HST-COS Observations of AGN. I. Ultraviolet Composite Spectra of the Ionizing Continuum and Emission Lines
类星体和其他活动星系核(AGN)的电离通量对于解释AGN的发射谱以及星系际介质的光电离和加热都是至关重要的。利用哈勃太空望远镜(HST)上的宇宙起源摄谱仪(COS)的紫外光谱,我们直接测量了22个活动星系核的静止标架电离连续谱和发射谱线。在0.026 < z < 1.44的红移范围内,COS对莱曼连续谱和许多远紫外发射线(Lya 1216,C IV 1549,Si IV/OIV] 1400,N V 1240,O VI 1035)进行采样。具有14-22 eV激发能的强EUV发射线(Ne VIII 770,780,Ne V 569,O II 834,O III 833,702,O IV 788,608,554,O V 630,N III 685)表明在宽发射线区域中存在热气体。静止坐标系连续谱F_nu ~ nu^{alpha_nu}在低于1000 A的波长处显示出断裂,其中FUV(1200-2000 A)中的光谱指数alpha_nu = -0.68 +/- 0.14变陡至EUV(500-1000 A)中的alpha_nu = -1.41 +/- 0.21。COS的EUV指数与2002年HST/FOS巡天中射电宁静活动星系核的EUV指数相似(alpha_nu = -1.57 +/-0.17)。在活动星系核复合物中,我们没有看到Lyman边(τ HI < 0.03)或He I 584发射…
The End of Helium Reionization at z~2.7 Inferred from Cosmic Variance in HST/COS HeII Lyman Alpha Absorption Spectra
本文报道了在两个z~3类星体的HST/COS光谱中探测到的强烈变化的星系际HeII吸收。从我们对这些和三个档案视线中的HeII吸收的均匀分析中,我们发现平均HeII有效光学深度从z~2.3处的τ ~1显著增加到z~3.2处的τ>5,但在2.7< z <3处的2<τ <5的大散射在~10 Mpc的尺度上。这种分散主要是由于HeII部分和HeII电离背景的波动,而不是密度变化,探测的同时代HI森林。HeII吸收的半解析模型需要HeII电离背景的强烈降低来解释在z>2.7时吸收的强烈增加,这可能表明HeII再电离在z>2.7时是不完全的。同样,最近的三维数值模拟的HeII再电离定性地同意观察到的趋势,只有当HeII再电离完成在z=2.7或甚至更低,如我们的五个视线中的两个在z<2.8的大tau>3所示。通过在2.7< z <3时将样本大小加倍,我们新发现的HeII视线首次探测了氦完全电离时第二次再电离时期的多样性。
We investigate the spatial distribution of Lyman-$α$ (Ly $α$) absorbers within cosmic voids. We create a catalogue of cosmic voids in Sloan Digital Sky Survey Data Release 7 (SDSS DR7) with the VoidFinder algorithm of the Void Analysis Software Toolkit (VAST). Using the largest catalogue of low-redshift (z $\leq$ 0.75) IGM absorbers to date, we identify 392 Ly $α$ absorbers inside voids. The fraction of Ly $α$ absorbers inside voids (65 per cent) is comparable to the volume filling fraction of voids (68 per cent), and significantly greater than the fraction of galaxies inside voids (21 per cen…
Multiple observations made by several different telescopes have shown asymmetry between the number of spiral galaxies rotating in opposite directions in different parts of the sky. One of the immediate questions regarding the possible asymmetry of the spin directions is whether the distribution forms a cosmological-scale axis. This paper analyzes and compares 10 different datasets published in the past decade, collected by SDSS, Pan-STARRS, and Hubble Space Telescope. The datasets contain spiral galaxies separated by their spin direction, and the distribution can show dipole axes. The analysis…
Accurate weak lensing mass estimates of clusters are needed in order to calibrate mass proxies for the cosmological exploitation of galaxy cluster surveys. Such measurements require accurate knowledge of the redshift distribution of the weak lensing source galaxies. In this context, we investigate the accuracy of photometric redshifts (photo-$z$s) computed by the 3D-HST team for the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields, which provide a relevant photometric reference data set for deep weak lensing studies. Through the comparison to spectroscopic redshifts and ph…
HST/COS Observations of the Ly alpha Forest toward the BL Lac Object 1ES1553+113
本文介绍了BL Lac天体1 ES 1553 +113的宇宙起源摄谱仪(HST/COS)在1135-1795波长范围内的新的远紫外光谱。数据显示了一个平滑的连续谱,在ISM和IGM中产生了丰富的窄吸收特征。这些特征包括41个0<z<0.43的Lya吸收体,其中14个在多个莱曼线中检测到,6个在一个或多个金属线中检测到。我们分析了在z=0.188处的Lya吸收剂的富金属三重态,其中检测到OVI、NV和CIII吸收。硅离子(SiIII/IV)未被检测到相当强的上限,并且我们使用测量的SiIII/CIII上限来推导吸收剂络合物的最强组分的丰度极限[C/Si]>0.6。星系红移巡天显示,许多大质量星系的红移与这个吸收复合体大致相同,这表明它产生于大尺度的星系细丝中。1 ES 1553 +113是最亮的河外X射线源和γ射线源之一,是高能天体物理学界的重要研究对象。1 ES 1553 +113没有固有的发射或吸收特性,因此没有直接的红移测定。我们使用介入的Lya吸收体对红移进行直接限制:基于确认的Lya+OVI吸收体的z_em>0.395,基于Lya的单线检测的z_em>0.433。COS/FUV数据仅对z<0.47的Lya吸收体敏感,但我们提出了z_em 0.4的统计参数<0.58 based on the non-detection of any Lyb absorbers at z…
UV Luminosity Functions from HST and JWST: A Possible Resolution to the High-Redshift Galaxy Abundance Puzzle and Implications for Cosmic Strings
McGill University(麦吉尔大学);The University of Texas at Austin(德克萨斯大学奥斯汀分校);Cosmic Frontier Center, The University of Texas at Austin(德克萨斯大学奥斯汀分校宇宙前沿中心);Massachusetts Institute of Technology(麻省理工学院);Center for Theoretical Physics, A Leinweber Institute, Massachusetts Institute of Technology(麻省理工学院莱因韦伯理论物理中心)