From Galaxy to Intergalactic Medium -- the Magnetic Connection in the Age of the Square Kilometre Array

我计划探测和描述星系的“深晕”。这些是气体晕，主要由宇宙射线和磁场组成，围绕着螺旋星系。 这样做的方法是瞄准视线边缘的星系。 当我们用肉眼观察这些星系时，它们看起来像天空中的一条细线，因为它们的方向是边缘。 我们的眼睛可以探测到来自星系中恒星的可见光，而恒星大多局限于一个薄的螺旋状圆盘中。 然而，当我们观察无线电波的波长时，我们开始看到围绕着这些圆盘的微弱的光晕发射。无线电晕从圆盘延伸到如此之远，以至于边缘上的星系看起来不再像一条细线。 事实上，我已经表明（通过叠加以前的数据），当在无线电波段观察时，大多数边缘上的螺旋星系看起来几乎是球形的。 在银河系中可能也是如此，虽然在我们自己的银河系中很难看到这一点，因为我们在银河系中的位置。但是如果我们可以从太阳的位置进行这样的测量，我们很可能会发现光环向上的范围（远离太阳所在的平面）大于从太阳到银河系中心的距离！深晕是一种甚至超出我上面描述的范围（超过大约10 kpc）的晕。我们有充分的理由相信，由于我们对星系内部和周围的磁场和宇宙射线的了解，这种晕是存在的，但它们以前从未被探测到。 已经掌握的数据以及利用新墨西哥州的甚大阵列和南非的MeerKat望远镜（平方公里阵列的前身）进行的拟议新观测将实现这一目标。 即使是更接近星系盘的晕，也可以通过分析磁场强度和宇宙射线能量来揭示它们的秘密。 这样的分析导致了盘和星系际介质之间的明确联系。 晕和深晕与我们在地球周围看到的相似。 地球被一个磁场（货车艾伦带）所包围，这个磁场不断受到来自太阳的宇宙射线的轰击。 能量场会因应这股太阳风而调整和扭曲，但仍然保持完整。 对于星系，我正在探测类似于货车艾伦带的星系。 有时，从鸟瞰图中观察大型系统所获得的见解可以应用于较小的局部系统。参与这一过程的学生将获得高水平的科学和技术专业知识。 他们将参与“大数据”科学，这是一个令人兴奋的项目，推动了当前知识的界限。他们将学习使用许多TB的数据进行精确的图像处理。 我以前的NSERC计划导致了四个新闻稿，其中加拿大是国际特色。下一步可能会产生更多。

I plan to detect and characterize `deep halos' of galaxies. These are gaseous halos, mainly consisting of cosmic rays and magnetic fields, that surround spiral galaxies.  The way to do this is to target galaxies that are edge-on to the line of sight.  When we look at such galaxies with the human eye, they look like a thin line in the sky because of their edge-on orientation.  Our eyes detect the optical light from stars in the galaxy and stars are mostly confined to a thin, spiral-like disk.  However, when we look at radio wavelengths, we start to see the faint halo emission that surrounds these disks. Radio halos extend so far from the the disk that edge-on galaxies no longer look like a thin line.  In fact, I have already shown (from stacking previous data) that most edge-on spiral galaxies look almost spherical when observed at radio wavelengths.  This is probably the case in the Milky Way as well, although it is harder to see this in our own Galaxy because of our location within it.  But if we could make such a measurement from the position of the Sun, we would likely find that the halo extent upwards(away from the plane where the Sun resides) is greater than the distance from the Sun to the Galactic Center! A deep halo is a halo that extends beyond even what I have described above (beyond about 10 kpc). We have every reason to expect that such halos exist because of our knowledge of magnetic fields and cosmic rays in and around galaxies, yet they have never before been detected.  Data that are already in hand as well as proposed new observations using the Very Large Array in New Mexico and the  MeerKat telescope in South Africa (a precursor to the Square Kilometre Array)  will achieve this goal.  Even halos that are closer in to the galaxy disk can yield their secrets through an analysis of the magnetic field strengths and cosmic ray energies.  Such analyses lead to a clear connection between disks and the intergalactic medium.  Halos and deep halos are similar to what we see around the Earth.  The Earth is surrounded by a magnetic field (the van Allen belts) that is constantly bombarded by cosmic rays from the Sun.  The fields adjust and distort in response to this Solar Wind, but remain intact nevertheless.  For galaxies, I am probing the galactic analog of the van Allen belts.  Sometimes, insights gained from looking at a large system from a bird's eye view can be applied to smaller local systems. Students involved in this process will receive scientific and technical expertise at a high level.  They will take part in `big data' science in an exciting project that pushes the boundaries of current knowledge. They will learn to do accurate image processing using many Tbytes of data.  My previous NSERC program led to four press releases in which Canada is featured internationally. The next step is likely to produce even more.