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FOSSILs in the Galactic Halo

Published online by Cambridge University Press:  30 October 2019

Carl J. Grillmair Open the ORCID record for Carl J. Grillmair [Opens in a new window]
Carl J. Grillmair*
Affiliation:
IPAC, Mail Code 314-6, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, U.S.A. email: carl@ipac.caltech.edu
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Abstract

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We use a matched filter to detect compact groups of old, metal-poor stars that we term FOSSILs (Fragments of Old Stellar Systems in Limbo). With size scales on the order of 10 arcminutes, distances ranging from 2 to 200 kpc, and memberships ranging from a handful to several dozen stars, these FOSSILs stand out from the surrounding field and are presumably signatures of, or debris from, ancient star clusters and dwarf galaxies. They may be localized concentrations of stars within more extensive tidal streams, and in some cases may be the signatures of extant but heretofore undetected ultrafaint galaxies. Using magnitudes and colors from the Pan-STARRs survey, we detect ∼ 70 such FOSSILs at 5 σ or greater in a 2200 square degree region in the vicinity of the north Galactic pole. A subsample of more populous FOSSILs that could be candidate ultrafaint dwarf galaxies suggests a total population of 200 such objects within 200 kpc of the Galactic center. Spectroscopic and astrometric follow-up of these FOSSILs will be required to determine the nature of these structures, deepen our understanding of the make-up and accretion history of the Galactic halo, and perhaps alleviate the missing satellites problem.

Keywords

Galaxy: halogalaxies: dwarf
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 14 , Symposium S344: Dwarf Galaxies: From the Deep Universe to the Present , August 2018 , pp. 73 - 76
Copyright
© International Astronomical Union 2019 

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