The QUEST RR Lyrae Survey II: The Halo Overdensities in the First Catalog

• Main Authors: Vivas, A. Katherina, Zinn, Robert
• Format: Journal Article
• Language: English
• Published: 17-04-2006
• Subjects: Physics - Astrophysics of Galaxies; Physics - Cosmology and Nongalactic Astrophysics; Physics - Earth and Planetary Astrophysics; Physics - High Energy Astrophysical Phenomena; Physics - Instrumentation and Methods for Astrophysics; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.astro-ph/0604359

Astron.J.132:714-728,2006 The first catalog of the RR Lyrae stars (RRLS) in the Galactic halo by the
QUEST Survey has been searched for significant overdensities that may be debris
from disrupted dwarf galaxies or globular clusters. Away from the major
overdensities, the distribution of these stars is adequately fit by a smooth
halo model, in which the flattening of the halo decreases with increasing
galactocentric distance (Preston et al 1991). This model was used to estimate
the ``background'' of RRLS on which the halo overdensities are overlaid. A
procedure was developed for recognizing groups of stars that constitute
significant overdensities with respect to this background. To test this
procedure, a Monte Carlo routine was used to make artificial RRLS surveys that
follow the smooth halo model, but with Poisson distributed noise in the numbers
of RRLS and, within limits, random variations in the positions and magnitudes
of the artificial stars. The artificial surveys created by this routine were
examined for significant groups in exactly the same way as the QUEST survey.
These calculations provided estimates of the frequencies with which random
fluctuations produce significant groups. In the QUEST survey, there are six
significant overdensities that contain six or more stars and several smaller
ones. The small ones and possibly one or two of the larger ones may be
artifacts of statistical fluctuations, and they need to be confirmed by
measurements of radial velocity and/or proper motion. The most prominent groups
are the northern stream from the Sagittarius dwarf spheroidal galaxy and a
large group in Virgo. Two other groups lie in the direction of the Monoceros
stream and at approximately the right distance for membership. Another group is
related to the globular cluster Palomar 5.