Spectroscopic Confirmation of the Pisces Overdensity

Juna A. Kollmeier (1) , Andrew Gould (2) , Stephen Shectman (1) , Ian B. Thompson (1) , George W. Preston (1) , Joshua D. Simon (1) , Jeffrey D. Crane (1) , \v{Z}eljko Ivezi\'c (3)

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Branimir Sesar (3) ((1) Carnegie Observatories (2) The Ohio State University (3) University of Washington)

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classification 🌌 astro-ph.GA astro-ph.CO

keywords overdensitystarsphotometricpiscesconfirmationgalaxylyraeradial

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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 (SDSS) at an estimated photometric distance of ~85kpc. We measure radial velocities for 8 RR Lyrae stars within Pisces. We find that 5 of the 8 stars have heliocentric radial velocities within a narrow range of -87 km/s < v < -67 km/s, 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 3 stars differ from one another by only 9 km/s, but it would be premature to identify them as a second system.

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Spectroscopic Confirmation of the Pisces Overdensity

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