Discovery of a rich proto-cluster at z = 2.9 and associated diffuse cold gas in the VIMOS Ultra-Deep Survey (VUDS)-猫眼课题宝

DOI：

10.1051/0004-6361/201423811

发表时间：

2014-03

期刊：

Astronomy and Astrophysics

影响因子：

6.5

通讯作者：

中科院分区：

物理与天体物理2区

文献类型：

作者：

O. Cucciati;O. Cucciati;G. Zamorani;B. Lemaux;S. Bardelli;A. Cimatti;A. Cimatti;O. Fèvre;P. Cassata;P. Cassata;B. Garilli;V. Brun;D. Maccagni;L. Pentericci;L. Tasca;R. Thomas;E. Vanzella;E. Zucca;R. Amorín;P. Capak;L. Cassarà;M. Castellano;J. Cuby;S. D. Torre;A. Durkalec;A. Fontana;M. Giavalisco;A. Grazian;N. Hathi;O. Ilbert;C. Moreau;S. Paltani;B. Ribeiro;M. Salvato;D. Schaerer;D. Schaerer;M. Scodeggio;V. Sommariva;V. Sommariva;M. Talia;Y. Taniguchi;L. Tresse;D. Vergani;P. W. Wang;S. Charlot;T. Contini;S. Fotopoulou;C. López-Sanjuan;Y. Mellier;N. Scoville

高密度环境是研究星系中等级结构形成与恒星质量增长之间联系的关键场所。在这项工作中，我们利用VIMOS超深巡天（VUDS）的光谱样本，描述了我们在COSMOS领域发现的z = 2.895处的一个巨大的原始星团。这是在活动星系核（AGN）或射电星系周围发现的罕见的z ~ 3结构之一，因此它代表了研究致密环境中星系形成的理想实验室。该结构由12个星系组成，在~ 7 ‘ × 8 ’的范围内具有安全的光谱红移，总z范围为Δz = 0.016。测量的星系数过密度为δ_g = 12±2。在13 × 15 × 17 Mpc^3的体积中，这个过密度的总质量为M ~ 8.1 × 10^(14) M_⊙。模拟结果表明，在z = 2.9处的超密度是一个原星团，它将坍缩成一个总质量为M_(z = 0) ~ 2.5 × 10^(15) M_⊙的星团，即局部宇宙中的一个大质量星团。我们分析了超密度内星系的特性，并将它们与相同红移但在超密度外的对照样本进行了比较。我们没有发现过密度内外星系的性质（恒星质量、恒星形成率、特定恒星形成率、NUV-r和r - K色）有统计学上的显著差异，但这一结果可能是由于缺乏统计，也可能是由于VUDS采样的特定星系群受环境的影响比其他未探测的星系群要小。在过密度背景下，星系的叠加光谱在Lyα红移波长z = 2.895 （λ = 4736 a）处表现出明显的吸收特征，静止帧等效宽度（EW）为4±1.4 a。在z ~ 2.9处仅对背景星系进行叠加，发现该吸收特征的静止帧EW为10.8±3.7 a，探测信噪比为~4。我们证实，这种测量不太可能是由于噪声波动。这些EW值暗示了一个高的柱密度(N(HI) ~ 3−20 × 10^(19) cm^(-2))，这与一种情况相一致，即这种吸收是由于落在原星系团星系晕势井中的气体冷流的介入。然而，我们不能排除这条吸收线与过密度内的扩散气体有关的假设。

High-density environments are crucial places for studying the link between hierarchical structure formation and stellar mass growth in galaxies. In this work, we characterise a massive proto-cluster at z = 2.895 that we found in the COSMOS field using the spectroscopic sample of the VIMOS Ultra-Deep Survey (VUDS). This is one of the rare structures at z ~ 3 not identified around an active galactic nucleus (AGN) or a radio galaxy, thus it represents an ideal laboratory for investigating the formation of galaxies in dense environments. The structure comprises 12 galaxies with secure spectroscopic redshift in an area of ~ 7′ × 8′, in a total z range of Δz = 0.016. The measured galaxy number overdensity is δ_g = 12 ± 2. This overdensity has a total mass of M ~ 8.1 × 10^(14) M_⊙ in a volume of 13 × 15 × 17 Mpc^3. Simulations indicate that such an overdensity at z ~ 2.9 is a proto-cluster, which will collapse in a cluster of total mass M_(z = 0) ~ 2.5 × 10^(15) M_⊙ at z = 0, i.e. a massive cluster in the local Universe. We analysed the properties of the galaxies within the overdensity, and we compared them with acontrol sample at the same redshift but outside the overdensity. We could not find any statistically significant difference between the properties (stellar mass, star formation rate, specific star formation rate, NUV-r and r − K colours) of the galaxies inside and outside the overdensity, but this result might be due to the lack of statistics or possibly to the specific galaxy population sampled by VUDS, which could be less affected by environment than the other populations not probed by the survey. The stacked spectrum of galaxies in the background of the overdensity shows a significant absorption feature at the wavelength of Lyα redshifted at z = 2.895 (λ = 4736 A), with a rest frame equivalent width (EW) of 4 ± 1.4 A. Stacking only background galaxies without intervening sources at z ~ 2.9 along their line of sight, we find that this absorption feature has a rest frame EW of 10.8 ± 3.7 A, with a detection S/N of ~4. We verify that this measurement is not likely to be due to noise fluctuations. These EW values imply a high column density (N(HI) ~ 3−20 × 10^(19) cm^(-2)), consistent with a scenario where such absorption is due to intervening cold streams of gas that are falling into the halo potential wells of the proto-cluster galaxies. Nevertheless, we cannot rule out the hypothesis that this absorption line is related to the diffuse gas within the overdensity.

Discovery of a rich proto-cluster at z = 2.9 and associated diffuse cold gas in the VIMOS Ultra-Deep Survey (VUDS)

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