Kinematics and simulations of the stellar stream in the halo of the Umbrella Galaxy
Distant ‘cannibal twin’ shows how galaxies grow
Not even a stream of stars from a long lost satellite galaxy dampens the clarity of this composite image featuring NGC 4651, the Umbrella galaxy. It was produced with the 8.2 meter Subaru telescope and the .5 meter instrument of the Blackbird Observatory.
Located towards the northern constellation of Coma Berenices, NGC 4651 drifts through the Cosmos about 62 million light years from Earth. It's noteworthy for the appearance of a crescent shaped structure extending laterally from an enormous jet that seems to emanate from the star system's heart. Combined, they conjure the appearance of an open umbrella, and its handle, shielding the galaxy from inclement cosmic weather.
Twenty years ago, astronomers using Anglo-Australian Telescope identified a new satellite galaxy, the Sagittarius dwarf, being engulfed by our own Milky Way Galaxy. This was the first sign that the Milky Way had acquired stars by snacking on other, smaller, galaxies. Since then, astronomers have spotted stellar streams in other star systems. According to the most widely accepted theory explaining the creation and evolution of galaxies, most spiral galaxies grew to their present size through the assimilation of dwarf satellite galaxies.
This new investigation, by an international team of astronomers led by Caroline Foster: (Australian Astronomical Observatory), is a follow-up to a 2010 study, led by David Martínez-Delgado (Heidelberg University), that used small robotic telescopes to image eight isolated spiral galaxies, and found the signs of mergers- shells, clouds and arcs of tidal debris- in six of them.
That study posited the Umbrella galaxy’s distinctive arc was the result of a single merger, rather than of several events over time.
This study uses the power of both the Subaru and Keck telescopes and confirms the crescent shaped shell at the end of the jet is the apocenter of a dwarf galaxy that was tidally disrupted then integrated into the larger spiral billions of years ago. Computer simulations indicate dwarf satellite galaxies sometimes yo-yo back and forth, disgorging stellar material at their terminus points, when their orbits are inclined close to the parent's spiral disk. This investigation also identified the nucleus of the progenitor satellite galaxy that formed the large spiral's fantastic surrounding stellar structures.
Obtained with the National Observatory of Japan's 8.2 meter Subaru telescope, this composite image of NGC 4651 was produced by combining G, R, and OIII narrow band filtered images into a synthetic luminance channel. The luminance data was scaled then projected into a gray scale picture. The exposures ranged from less than 2 minutes to slightly over 5 minutes in duration. The final composite image was tinted with data exposed through the Blackbird Observatory .5 meter telescope. The color exposures required a total of six hours.
For more information also read:
A Pilot Survey with Modest Aperture Telescopes
The survey's full PDF documentation
The Formation and Evolution of Galaxies
The Model Universe