NOAO: Hiding in Plain Sight - The Densest Galaxies Known

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NOAO: Hiding in Plain Sight - The Densest Galaxies Known

Post by bystander » Mon Jul 27, 2015 6:55 pm

Hiding in Plain Sight: The Densest Galaxies Known
National Optical Astronomy Observatory | 2015 July 27
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Two undergraduates at San Jose State University have discovered two galaxies that are the densest known. Similar to ordinary globular star clusters but a hundred to a thousand times brighter, the new systems have properties intermediate in size and luminosity between galaxies and star clusters.

The first system discovered by the investigators, M59-UCD3, has a width two hundred times smaller than our own Milky Way Galaxy and a stellar density 10,000 times larger than that in the neighborhood of the Sun. For an observer in the core of M59-UCD3, the night sky would be a dazzling display, lit up by a million stars. The stellar density of the second system, M85-HCC1, is higher still: about a million times that of the solar neighborhood. Both systems belong to the new class of galaxies known as ultracompact dwarfs (UCDs).

The study, led by undergraduates Michael Sandoval and Richard Vo, used imaging data from the Sloan Digital Sky Survey, the Subaru Telescope, and the Hubble Space Telescope, as well as spectroscopy from the Goodman Spectrograph on the Southern Astrophysical Research (SOAR) Telescope, located on the Cerro Tololo Inter-American Observatory site. The National Optical Astronomy Observatory (NOAO) is a SOAR partner. The SOAR spectrum was used to show that M59-UCD3 is associated with a larger host galaxy, M59, and to measure the age and elemental abundances of the galaxy’s stars.

“Ultracompact stellar systems like these are easy to find once you know what to look for. However, they were overlooked for decades because no one imagined such objects existed: they were hiding in plain sight,” said Richard Vo. “When we discovered one UCD serendipitously, we realized there must be others, and we set out to find them.” ...

Hiding in plain sight: record-breaking compact stellar systems in the Sloan Digital Sky Survey - Michael A. Sandoval et al
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Two ultra-dense galaxies (insets) have been discovered orbiting larger host <br />galaxies. The compact systems are thought to be the remnants of once <br />normal galaxies that were swallowed by the host, a process that removed <br />the fluffy outer parts of the systems, leaving the dense centers behind. <br />Credit: A. Romanowsky (SJSU), Subaru, Hubble Legacy Archive
Two ultra-dense galaxies (insets) have been discovered orbiting larger host
galaxies. The compact systems are thought to be the remnants of once
normal galaxies that were swallowed by the host, a process that removed
the fluffy outer parts of the systems, leaving the dense centers behind.
Credit: A. Romanowsky (SJSU), Subaru, Hubble Legacy Archive
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