New Signatures of the Milky Way Formation in the Local Halo and Inner-halo Streamers in the Era of Gaia

Journal
Date Issued
2015
Author(s)
•
•
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DOI
Description
We are grateful to the referee for comments that helped us improve the original manuscript. This work has been partially funded by ASI, under contract to INAF I/058/10/0 “ Gaia Mission—The Italian Participation to DPAC,” and by MIUR, through PRIN 2012 grant No. 1.05.01.97.02 “Chemical and dynamical evolution of our Galaxy and of the galaxies of the Local Group.” M.G.L. acknowledges support from the Chinese Academy of Sciences through 2015 CAS President’s International Fellowship Initiative (PIFI) for Visiting Scientists.
Abstract
We explore the vicinity of the Milky Way through the use of spectrophotometric data from the Sloan Digital Sky Survey and high-quality proper motions derived from multi-epoch positions extracted from the Guide Star Catalog II database. In order to identify and characterize streams as relics of the Milky Way formation, we start with classifying, selecting, and studying 2417 subdwarfs with [Fe/H] < -1.5 up to 3 kpc away from the Sun as tracers of the local halo system. Then, through phase-space analysis, we find statistical evidence of five discrete kinematic overdensities among 67 of the fastest-moving stars and compare them to high-resolution N-body simulations of the interaction between a Milky Way-like galaxy and orbiting dwarf galaxies with four representative cases of merging histories. The observed overdensities can be interpreted as fossil substructures consisting of streamers torn from their progenitors; such progenitors appear to be satellites on prograde and retrograde orbits on different inclinations. In particular, of the five detected overdensities, two appear to be associated, yielding 21 additional main-sequence members, with the stream of Helmi et al. that our analysis confirms is on a high-inclination prograde orbit. The three newly identified kinematic groups could be associated with the retrograde streams detected by Dinescu and Kepley et al.; whatever their origin, the progenitor(s) would be on retrograde orbit(s) and inclination(s) within the range 10° - 60°. Finally, we use our simulations to investigate the impact of observational errors and compare the current picture to the promising prospect of highly improved data expected from the Gaia mission.
Volume
150
Issue
4
Start page
128
Uri
Url
Issn Identifier
0004-6256
Ads BibCode
2015AJ....150..128R
Rights
open.access
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