TY - JOUR
T1 - Boötes III is a Disrupting Dwarf Galaxy Associated with the Styx Stellar Stream
AU - Carlin, Jeffrey L.
AU - Sand, D. J.
N1 - Funding Information:
D.J.S. acknowledges B. Mutlu-Pakdil for providing photometry advice. Research by D.J.S. is supported by NSF grants AST-1821987 and 1821967.
Funding Information:
This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/ gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC,https://www.cosmos.esa.int/web/gaia/ dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved..
PY - 2018/9/20
Y1 - 2018/9/20
N2 - We present proper motion (PM) measurements of Boötes III, an enigmatic stellar satellite of the Milky Way (MW), utilizing data from the second data release of the Gaia mission. By selecting 15 radial velocity confirmed members of Boötes III, along with a likely RR Lyrae member in the vicinity, we measure an error-weighted mean PM of (μ μ δ) = (-1.14, -0.98)+(0.18, 0.20) mas yr-1. We select and present further stars that may be Boötes III members based on their combined PM and position in the color-magnitude diagram. We caution against assigning membership to stars that are not confirmed spectroscopically, as we demonstrate that there are contaminating stars from the disrupting globular cluster NGC 5466 in the vicinity of the main body of Boötes III, but we note that our results are consistent with previous Boötes III PM estimates that did not include spectroscopic members. Based on the measured PM and other known properties of Boötes III, we derive its Galactocentric velocity and compute its orbit given canonical MW potentials with halo masses of both 0.8 1012 M o and 1.6x1012 M o. These orbits robustly show that Boötes III passed within ∼12 kpc of the Galactic center on an eccentric orbit roughly ∼140 Myr ago. Additionally, the PM of Boötes III is in excellent agreement with predictions for the retrograde motion of the coincident Styx stellar stream. Given this, along with the small pericenter and metallicity spread of Boötes III itself, we suggest that it is a disrupting dwarf galaxy giving rise to the Styx stellar stream.
AB - We present proper motion (PM) measurements of Boötes III, an enigmatic stellar satellite of the Milky Way (MW), utilizing data from the second data release of the Gaia mission. By selecting 15 radial velocity confirmed members of Boötes III, along with a likely RR Lyrae member in the vicinity, we measure an error-weighted mean PM of (μ μ δ) = (-1.14, -0.98)+(0.18, 0.20) mas yr-1. We select and present further stars that may be Boötes III members based on their combined PM and position in the color-magnitude diagram. We caution against assigning membership to stars that are not confirmed spectroscopically, as we demonstrate that there are contaminating stars from the disrupting globular cluster NGC 5466 in the vicinity of the main body of Boötes III, but we note that our results are consistent with previous Boötes III PM estimates that did not include spectroscopic members. Based on the measured PM and other known properties of Boötes III, we derive its Galactocentric velocity and compute its orbit given canonical MW potentials with halo masses of both 0.8 1012 M o and 1.6x1012 M o. These orbits robustly show that Boötes III passed within ∼12 kpc of the Galactic center on an eccentric orbit roughly ∼140 Myr ago. Additionally, the PM of Boötes III is in excellent agreement with predictions for the retrograde motion of the coincident Styx stellar stream. Given this, along with the small pericenter and metallicity spread of Boötes III itself, we suggest that it is a disrupting dwarf galaxy giving rise to the Styx stellar stream.
KW - galaxies: individual (Bootes III)
KW - galaxies: interactions
KW - galaxies: kinematics and dynamics
KW - proper motions
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U2 - 10.3847/1538-4357/aad8c1
DO - 10.3847/1538-4357/aad8c1
M3 - Article
AN - SCOPUS:85053896583
SN - 0004-637X
VL - 865
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 7
ER -