Observations of neutral hydrogen can provide a wealth of information about the kinematics of galaxies. To learn more about the large scale structures and accretion processes, the extended environment of galaxies have to be observed. Numerical simulations predict a cosmic web of extended structures and gaseous filaments. To observe the direct vicinity of galaxies, column densities have to be achieved that probe the regime of Lyman limit systems. Typically HI observations are limited to a brightness sensitivity of NHI ~ 10^19 cm-2 but this has to be improved by ~2 orders of magnitude. With the Westerbork Synthesis Radio Telescope (WSRT) we map the galaxy filament connecting the Virgo Cluster with the Local Group. About 1500 square degrees on the sky is surveyed, with Nyquist sampled pointings. By using the WSRT antennas as single dish telescopes instead of the more conventional interferometer we are very sensitive to extended emission. The survey consists of a total of 22,000 pointings and each pointing has been observed for 2 minutes with 14 antennas. We reach a flux sensitivity of 16 mJy beam-1 over 16 km s-1, corresponding to a brightness sensitivity of NHI ~ 3.5 \times 10^16 cm-2 for sources that fill the beam. At a typical distance of 10 Mpc probed by this survey, the beam extent corresponds to about 145 kpc in linear scale. Although the processed data cubes are affected by confusion due to the very large beam size, we can identify most of the galaxies that have been observed in HIPASS. Furthermore we made 20 new candidate detections of neutral hydrogen. Several of the candidate detections can be linked to an optical counterpart. The majority of the features however do not show any signs of stellar emission. Their origin is investigated further with accompanying HI surveys which will be published in follow up papers.
Velocity fields and turbulence from cosmic filaments to galaxy clusters
Université Paris-Saclay（巴黎萨克雷大学）；CNRS（法国国家科学研究中心）；Institut d’Astrophysique Spatiale（天体物理研究所）；The Open University of Israel（以色列开放大学）；Kapteyn Astronomical Institute（卡普坦天文研究所）；University of Groningen（格罗宁根大学）；Université de Lille（里尔大学）；Centrale Lille（里尔中央理工学院）；CRIStAL（晶体与材料研究中心）
我们探索的结构和运动学之间的本地虚空和室女星系团居住的星系分散的灯丝。为此目的，我们考虑了在RA = [13.0.]的天区内的361个径向速度为$V_{LG} < 2000$ km/s的星系样本。18.0] $^h$和Dec.= [ $-$ 5. $+$ 10] $^\circ$。目前，其中161个有单独的距离估计。沿着这条带的星系分布以奇特的速度呈现出在RA 17 $^h$处已知的以室女座为中心的坍< 14 $^h$ and some signs of outflow from the Local Void at RA >缩。大多数牧夫座带状星系（56%）属于13个星系群和11对星系，其中最突出的星系群围绕着NGC 5846。牧夫座带星系群位于[17 $-$ 27]Mpc内，比室女星系团离我们更远。牧夫座暗条包含$2.7\times10^{12} M_\odot$的总恒星质量和$9.07\times10^{13} M_\odot$的总维里质量，暗物质的平均密度为$Ω_m = 0.09$，比全球宇宙平均密度低三倍。
