The VISTA Deep Extragalatic Observations (VIDEO) Survey

在过去的十年里，天文学研究取得了长足的进步。我们现在知道宇宙的主要组成部分是暗物质、暗能量和正常物质，也就是我们能够直接观察到的物质。有了这些参数，我们就能够研究宇宙中发生的物理过程。其中一个最基本的问题是，星系和其中的恒星和黑洞是如何在宇宙的历史上形成的。要做到这一点，我们需要看得既远又广；远是因为我们需要追溯到第一批星系形成的时间，而有限的光速意味着我们通过看得越来越远来做到这一点，甚至到宇宙不到10亿岁(宇宙目前约130亿岁)的时候也是如此；宽是因为星系的形成和演化方式可能会受到它们所在环境的严重影响。例如，人们可能会想象，宇宙中最大质量的星系将被最大质量的星系团包围，因为所有的星系都通过引力相互吸引，因此大质量星系可能比质量较低的星系吸引更多的星系。因此，我们需要俯瞰大片天空，才能全面了解星系的形成和演化。显然，如果深入调查，径向的交易量会更大。因此，大多数银河系外天文观测现在都有一种婚礼蛋糕结构，最深、最窄的观测类似于婚礼蛋糕的顶层，而最宽、最浅的观测类似于最低层的观测。所有这些调查都吻合在一起，因为它们探索了不同但具有代表性的宇宙卷。Vista深星系外观测(视频)调查是一项约200夜的调查，将在未来五年内在智利帕拉纳尔的Vista近红外望远镜上进行。这是与Vista进行的第二深入的调查，因此也是婚礼蛋糕中第二高的调查。它将解决的科学问题涉及面很广，但都涉及星系在宇宙历史上如何形成和演化，以及这可能如何取决于它们所处的环境。它的深度足以探测到最大质量的星系，当时它们刚刚开始形成，宽度足以探测到宇宙年龄约90%以上的整个环境密度范围。此外，调查将在红外波长进行，在那里，主宰大质量星系的旧恒星发射出它们的大部分辐射。这使我们能够更好地估计星系的质量，而不是在光学波长下工作，在光学波长上，任何恒星形成活动都可以增强较蓝光波段的发射，导致对星系质量的非常不确定的估计。我们还知道，许多恒星形成活动和物质聚集在超大质量黑洞上发出的光都被尘埃遮住了。这种尘埃熄灭了星系的蓝光，因此再次在红外线中观察可以得到更清晰的银河系图像。在视频调查完成后，我们将对宇宙历史上支配星系形成和演化的物理过程有一个更加清晰的认识。

Astronomy research has come a long way in the past decade. We now know the principal consituents of the Universe in the form of Dark Matter, Dark Energy and normal matter, the material we are able to observe directly. With these parameters now in place we are able to investigate the physical processes which occur in the Universe. One of the most fundamental questions is how the galaxies and the stars and black holes which reside in them are built up over the history of the Universe. To do this we are required to look both far and wide; far because we need to look back in time to when the first galaxies were forming and the finite speed of light means that we do this by looking further and further away, even up to a time when the Universe was less that 1 billion years old (the Universe is currently about 13billion years old); and wide because the way in which galaxies form and evolve can be heavily influenced by the environment in which they reside. For example, one might imagine that the most massive galaxies in the Universe would be surrounded by the most massive cluster of galaxies as all galaxies are attracted to each other via gravity, so massive galaxy may attract more galaxies than a lower mass galaxy. Therefore, we need to look over large areas of the sky in order to get a full picture of galaxy formation and evolution. Obviously, if one goes deep then there is more volume surveyed in the radial direction. Thus, most extragalactic astronomical surveys now have a wedding-cake structure, with the deepest narrowest survey analagous to the top-tier of the wedding cake, and the widest shallowest surveys analagous to the lowest tier. All of these surveys fit together as they probe different but representative volumes of the Universe. The VISTA Deep Extragalactic Observations (VIDEO) survey is a ~200 night survey which will be carried out on the VISTA near-infrared telescope in Paranal, Chile, over the next five years. It is the second deepest survey to be carried out with VISTA, and thus the second highest tier in the wedding cake. The science questions that it will address are wide-ranging but all are concerned with how galaxies form and evolve over the history of the Universe and how this may depend on their environment. It is deep enough to detect the most massive galaxies at a time when they were first beginning to form and wide enough to probe the whole range of environmental density over ~90% of the age of the Universe. Furthermore, the survey will be carried out at infrared wavelengths, where the old stars which dominate massive galaxies emit the bulk of their radiation. This allows us to estimate the mass of the galaxies much better than if we were to work at optical wavelengths where any star-formation activity can boost the emission in the bluer optical bands, leading to a very uncertain estimate of the galaxy mass. We also know that much of the star-formation activity and the light emitted from material acccreting onto a supermassive black hole is obscured by dust. This dust extinguishes the blue light of a galaxy, thus observing in the infrared again gives a much clearer picture of the galaxy. On the completion of the VIDEO survey we will have a much clearer idea of the physical processes governing galaxy formation and evolution over the history of the Universe.