与蜘蛛网星系有关的漫射UV光：星系外原位恒星形成的证据
Diffuse UV light associated with the Spiderweb Galaxy: evidence for in-situ star formation outside galaxies
摘要：
我们呈现了位于z=2的射电星系MRC 1138-262周围的60 kpc晕中的漫射紫外星系际光（IGL）的详细图像。我们讨论了IGL的性质，并排除了昏暗的星系团星系，星云连续发射，同步加速器，逆康普顿发射和银河恒星光散射的IGL的可能来源。尘埃散射的类星体光是一种不太可能的可能性，不能完全排除。我们的结论是，IGL的来源是最有可能是一个年轻的恒星星族分布在一个光环包围的无线电和卫星星系，经历恒星形成的速度大于57 Msun/年。在射电核心的70千秒差距内，大约44%的恒星形成都是以这种漫射模式进行的。IGL的平均紫外线颜色比星系的平均颜色更蓝，并且随着距离射电星系半径的增加，IGL有变蓝的趋势。星系和IGL的紫外线颜色-表面亮度的关系，可以得到的变化，无论是恒星星族年龄或灭绝。这些观测结果显示了一种不同的，但可能是重要的恒星形成模式，即本质上是扩散的。恒星的形成，如紫外光跟踪，在高红移宇宙中发生在两种模式：一个在通常的莱曼破碎星系团状模式的kpc尺度，和其他的扩散模式在一个大的区域周围的大规模增长的星系。这种恒星形成的模式很容易被高角分辨率观测所忽略，而高角分辨率观测非常适合于探测高表面亮度的致密星系。从这些结果推断，有可能大量的恒星形成发生在大部分质量星系的晕内的大扩展区域，这些星系形成于高红移。
英文摘要：
We present detailed images of diffuse UV intergalactic light (IGL), situated in a 60kpc halo that surrounds the radio galaxy MRC 1138-262 at z=2. We discuss the nature of the IGL and rule out faint cluster galaxies, nebular continuum emission, synchrotron, inverse Compton emission and scattering of galactic stellar light as possible sources of the IGL. Dust scattered quasar light is an unlikely possibility that cannot be ruled out entirely. We conclude that the source of the IGL is most likely to be a young stellar population distributed in a halo encompassing the radio and satellite galaxies, undergoing star formation at a rate greater than 57 Msun/yr. Within 70kpc of the radio core, approximately 44% of the star formation that is traced by UV light occurs in this diffuse mode. The average UV colour of the IGL is bluer than the average galaxy colour, and there is a trend for the IGL to become bluer with increasing radius from the radio galaxy. Both the galaxies and the IGL show a UV colour--surface brightness relation which can be obtained by variations in either stellar population age or extinction. These observations show a different, but potentially important mode of star formation, that is diffuse in nature. Star formation, as traced by UV light, occurs in two modes in the high redshift universe: one in the usual Lyman break galaxy clump-like mode on kpc scales, and the other in a diffuse mode over a large region surrounding massive growing galaxies. Such a mode of star formation can easily be missed by high angular resolution observations that are well suited for detecting high surface brightness compact galaxies. Extrapolating from these results, it is possible that a significant amount of star formation occurs in large extended regions within the halos of the most massive galaxies forming at high redshift.
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