DISENTANGLING THE VIRGO OVERDENSITY WITH RR LYRAE STARS
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Date
2016
Journal Title
Journal ISSN
Volume Title
Publisher
IOP PUBLISHING LTD
Abstract
We use a combination of spatial distribution and radial velocity to search for halo substructures in a sample of 412 RR Lyrae stars (RRLSs) that covers a. region of similar to 525 square degrees. of the Virgo overdensity (VOD) and spans distances from the Sun from 4 to 75 kpc. With a friends-of-friends algorithm we identified six high-significance groups of RRLSs in phase space, which we associate mainly with the VOD and with the Sagittarius stream. Four other groups were also flagged as less significant overdensities. Three high-significance and three. lower-significance groups have distances between similar to 10 and 20 kpc, which places them in the distance range attributed by others to the VOD. The largest of these is the Virgo stellar stream. at 19 kpc, which has 18 RRLSs, a factor of two increase over the number known previously. While these VOD groups are distinct according to our selection criteria, their overlap in position and distance. and, in a few cases, similarity in radial velocity are suggestive that they may not all stem from separate accretion events. Even so, the VOD appears to be caused by more than one overdensity. The Sagittarius (Sgr). stream is a very obvious feature in the background of the VOD at a mean distance of 44 kpc. Two additional high-significance. groups were detected at distances >40 kpc. Their radial velocities and locations differ from the expected path of the Sgr debris in this part of the sky, and they are likely to be remnants of other accretion events.
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Keywords
stars: variables: RR Lyrae, Galaxy: halo, stars: kinematics and dynamics, Galaxy: structure Supporting material: machine-readable tables, SAGITTARIUS DWARF GALAXY, MILKY-WAY, GALACTIC HALO, PROPER MOTIONS, VARIABLE SKY, IN-SITU, SUBSTRUCTURE, SDSS, SPECTROSCOPY, STREAM