天龙座的三重星系

2023年7月1日

Three Galaxies in Draco
Image Credit & Copyright: David Vernet, Jean-François Bax, Serge Brunier, OCA/C2PU

Explanation: This tantalizing trio of galaxies sometimes called the Draco Group, is located in the northern constellation of (you guessed it) Draco, the Dragon. From left to right are face-on spiral NGC 5985, elliptical galaxy NGC 5982, and edge-on spiral NGC 5981, all found within this single telescopic field of view that spans a little more than the width of the full moon. While the group is far too small to be a galaxy cluster, and has not been catalogued as a compact galaxy group, the three galaxies all do lie roughly 100 million light-years from planet Earth. Not as well known as other tight groupings of galaxies, the contrast in visual appearance still makes this triplet an attractive subject for astroimagers. On close examination with spectrographs, the bright core of striking spiral NGC 5985 shows prominent emission in specific wavelengths of light, prompting astronomers to classify it as a Seyfert, a type of active galaxy. This impressively deep exposure hints at a faint dim halo along with sharp-edged shells surrounding elliptical NGC 5982, evidence of past galactic mergers. It also reveals many even more distant background galaxies.

Tomorrow’s picture: over and under

天龙座的三重星系
影像提供与版权: David Vernet, Jean-François Bax, Serge Brunier, OCA/C2PU

说明: 这三个迷人的星系位于北天的天龙座内，偶有天龙群之称。在这片稍大于满月宽度的单一望远镜视野里，从左至右它们分别为：正向的螺旋星系NGC 5985、椭圆星系NGC 5982、及侧向的螺旋星系NGC 5981。这群距离约1亿光年远的星系因为过小，故未获得星系群或紧密群之分类。在使用光谱仪仔细探索正向螺旋星系NGC 5985之后，天文学家发现它的核心在某些波段有很强的辐射，故其分类为数类活跃星系之一的西佛星系。天龙三重星系虽然知名度不如其他紧密群，不过它们在视觉上的强烈对比，让它们经常成为天文摄影者的热门拍摄标的。在这幅让人印象深刻的深空影像里，椭圆星系NGC 5982的周围隐隐有暗淡的外晕及边界明确的壳层，显示它过去曾发生星系合并。此外，这幅影像也记录了许多更遥远的背景星系。