Free Astronomy Magazine July-August 2015

SPACE CHRONICLES T his is a Hubble Space Telescope image of the farthest spectroscopically con- firmed galaxy observed to date (inset). It was identified in this Hub- ble image of a field of galaxies in the CAN- DELS survey (Cosmic Assembly Near-infra- red Deep Extragalactic Legacy Survey). NASA's Spitzer Space Tele- scope also observed the unique galaxy. The W. M. Keck Ob- servatory was used to obtain a spectroscopic redshift (z=7.7), ex- tending the previous redshift record. Mea- surements of the stretching of light, or redshift, give the most reliable distances to other galaxies. This source is thus cur- rently the most dis- tant confirmed galaxy known, and it appears to also be one of the brightest and most massive sources at that time. The galaxy existed over 13 billion years ago. The near-infrared image of the galaxy (inset) has been colored blue as suggestive of its young, and hence very blue, stars. The CANDELS field is a combination of visible-light and near-infrared exposures. [NASA, ESA, P. Oesch and I. Momcheva (Yale University), and the 3D-HST and HUDF09/XDF Teams] kum of the Yale University, second author of the study. “Only the larg- est telescopes are powerful enough to reach to these large distances.” The discovery was only possible thanks to the relatively new MO- SFIRE instrument on the Keck I tele- scope, which allows astronomers to efficiently study several galaxies at the same time. Measuring galaxies at these ex- treme distances and characterizing their properties is a main goal of astronomy over the next decade. The observations see EGS-zs8-1 at a time when the Universe was under- going very important changes: the hydrogen between galaxies was transitioning from a neutral to an ionized state. “It appears that the young stars in the early galaxies like EGS-zs8-1 were the main drivers for this tran- sition called reionization,” said Ry- chard Bouwens of the Leiden Ob- servatory, co-author of the study. These new Keck Observatory, Hub- ble, and Spitzer observations to- gether also pose new questions. They confirm that massive galaxies already existed early in the histo- ry of the Universe, but that their physical properties were very differ- ent from galaxies seen around us today. Astronomers now have very strong evidence that the peculiar colors of early galaxies seen in the Spitzer Space Telescope images orig- inate from a very rapid formation of massive, young stars, which in- teracted with the primordial gas in these galaxies. n

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