Comprehensive Andromeda Study Hints of Violent History

W. M. Keck Observatory press release

Dots show locations of stars in the Keck Observatory spectroscopic survey superimposed on an image of Andromeda. Credit: Claire Dorman/ESA
Dots show locations of stars in the Keck Observatory spectroscopic survey superimposed on an image of Andromeda. Credit: Claire Dorman/ESA
A detailed study of the motions of different stellar populations in Andromeda galaxy by UC Santa Cruz scientists using W. M. Keck Observatory data has found striking differences from our own Milky Way, suggesting a more violent history of mergers with smaller galaxies in Andromeda’s recent past. The findings are being presented on Thursday, January 8, at the winter meeting of the American Astronomical Society in Seattle.

The structure and internal motions of the stellar disk of a spiral galaxy hold important keys to understanding the galaxy’s formation history. The Andromeda galaxy, also called M31, is the closest spiral galaxy to the Milky Way and the largest in the local group of galaxies.

“In the Andromeda galaxy we have the unique combination of a global yet detailed view of a galaxy similar to our own. We have lots of detail in our own Milky Way, but not the global, external perspective,” said Puragra Guhathakurta, professor of astronomy and astrophysics at the University of California, Santa Cruz.

The new study, led by UC Santa Cruz graduate student Claire Dorman and Guhathakurta, combined data from two large surveys of stars in Andromeda conducted at the Keck Observatory in Hawaii as well as data from the Hubble Space Telescope.

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Postcard from the Universe – Andromeda

So I shot M31… yet again. I admit I enjoy this target, it is just so much fun. I always think I can do a little bit better. It is color balance that has been my bugaboo lately, I have really been playing with my technique to achieve a decent color balance. Something aesthetically pleasing and something that bears at least a little resemblance to reality. I understand how objective these criteria are, but still… I try.

Be sure to click on the image to get the large version…

The Andromeda Galaxy, M31, taken 9Aug2013 at the Oregon Star Party, M32 and M110 are also visible, TV-76 with Canon 60D, 17x480s + 10x60s

A Vast Rotating Disk of Dwarf Galaxies Surrounding the Andromeda Galaxy

W. M. Keck Observatory press release

Astronomers using the Canada-France-Hawaii and W. M. Keck Observatory telescopes on the summit of Mauna Kea, Hawaii have been amazed to find a group of dwarf galaxies moving in unison in the vicinity of the Andromeda Galaxy. The structure of these small galaxies lies in a plane, analogous to the planets of the Solar System. Unexpectedly, they orbit the much larger Andromeda galaxy en masse, presenting a serious challenge to our ideas for the formation and evolution of all galaxies.

The findings are being reported on the cover the upcoming issue of the journal, Nature.

While Persian astronomers were the first to catalogue the Andromeda galaxy, only in the last five years that we have studied in exquisite detail the most distant suburbs of the Andromeda galaxy via the Pan-Andromeda Archaeological Survey (PAndAS), undertaken with the Canada-France-Hawaii Telescope and measured with the Keck Observatory, providing our first panoramic view of our closest large companion in the cosmos.

The study culminates many years of effort by an international team of scientists who have discovered a large number of the satellite galaxies, developed new techniques to measure their distances, and have used the Keck Observatory with colleagues to measure their radial velocities, or Doppler shifts (the speed of the galaxy relative to the Sun). While earlier work had hinted at the existence of this structure, the new study has demonstrated its existence to a high level of statistical confidence (99.998%).

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