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SPECTROSCOPIC CONFIRMATION OF THE PISCES OVERDENSITY*

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Juna A. Kollmeier1, Andrew Gould2, Stephen Shectman1, Ian B. Thompson1, George W. Preston1, Joshua D. Simon1, Jeffrey D. Crane1, Željko Ivezić3 and Branimir Sesar3

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We present spectroscopic confirmation of the "Pisces Overdensity," also known as "Structure J," a photometric overdensity of RR Lyrae stars discovered by the Sloan Digital Sky Survey at an estimated photometric distance of ~85 kpc. We measure radial velocities for eight RR Lyrae stars within Pisces. We find that five of the eight stars have heliocentric radial velocities within a narrow range of –87 km s-1 < vr < –67 km s-1, suggesting that the photometric overdensity is mainly due to a physically associated system, probably a dwarf galaxy or a disrupted galaxy. Two of the remaining three stars differ from one another by only 9 km s–1, but it would be premature to identify them as a second system.


Footnote
*  This Letter includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
Keywords

galaxies: dwarf; Galaxy: halo; Galaxy: structure; stars: individual (RR Lyrae)


PACS

95.75.Fg Spectroscopy and spectrophotometry

95.75.De Photography and photometry (including microlensing techniques)

97.10.Wn Proper motions and radial velocities (line-of-sight velocities); space motions

95.80.+p Astronomical catalogs, atlases, sky surveys, databases, retrieval systems, archives, etc.

98.52.Wz Dwarf galaxies (elliptical, irregular, and spheroidal)

97.30.Kn RR Lyrae stars; RV Tauri and PV Telescopii variables

Subjects

Astrophysics and astroparticles

Dates

Issue 2 (2009 November 10)

Received 2009 August 11, accepted for publication 2009 October 6

Published 2009 October 21



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