TY - JOUR
T1 - Evidence of Fanning in the Ophiuchus Stream
AU - Sesar, Branimir
AU - Price-Whelan, Adrian M.
AU - Cohen, Judith G.
AU - Rix, Hans-Walter
AU - Pearson, Sarah
AU - Johnston, Kathryn V.
AU - Bernard, Edouard J.
AU - Ferguson, Annette M. N.
AU - Martin, Nicolas F.
AU - Slater, Colin T.
AU - Chambers, Kenneth C.
AU - Flewelling, Heather
AU - Wainscoat, Richard J.
AU - Waters, Christopher
PY - 2016/1/1
Y1 - 2016/1/1
N2 - The Ophiuchus stellar stream presents a dynamical puzzle: its oldstellar populations (˜12 Gyr) cannot be reconciled with (1) itsorbit in a simple model for the Milky Way potential and (2) its shortangular extent, both of which imply that the observed stream formedwithin the last <1 {{Gyr}}. Recent theoretical work has shown thatstreams on chaotic orbits may abruptly fan out near their apparent ends;stars in these fans are dispersed in both position and velocity and maybe difficult to associate with the stream. Here we present the firstevidence of such stream-fanning in the Ophiuchus stream, traced by fourblue horizontal branch stars beyond the apparent end of the stream.These stars stand out from the background by their high velocities({v}{{los}}> 230 km s-1) against ˜40other stars: their velocities are comparable to those of the stream, butwould be exceptional if they were unrelated halo stars. Their positionsand velocities are, however, inconsistent with simple extrapolation ofthe observed cold, high-density portion of the stream. Theseobservations suggest that stream-fanning may be a real, observableeffect and, therefore, that Ophiuchus may be on a chaotic orbit. Theyalso show that the Ophiuchus stream is more extended and hencedynamically older than previously thought, easing the stellar populationversus dynamical age tension.
AB - The Ophiuchus stellar stream presents a dynamical puzzle: its oldstellar populations (˜12 Gyr) cannot be reconciled with (1) itsorbit in a simple model for the Milky Way potential and (2) its shortangular extent, both of which imply that the observed stream formedwithin the last <1 {{Gyr}}. Recent theoretical work has shown thatstreams on chaotic orbits may abruptly fan out near their apparent ends;stars in these fans are dispersed in both position and velocity and maybe difficult to associate with the stream. Here we present the firstevidence of such stream-fanning in the Ophiuchus stream, traced by fourblue horizontal branch stars beyond the apparent end of the stream.These stars stand out from the background by their high velocities({v}{{los}}> 230 km s-1) against ˜40other stars: their velocities are comparable to those of the stream, butwould be exceptional if they were unrelated halo stars. Their positionsand velocities are, however, inconsistent with simple extrapolation ofthe observed cold, high-density portion of the stream. Theseobservations suggest that stream-fanning may be a real, observableeffect and, therefore, that Ophiuchus may be on a chaotic orbit. Theyalso show that the Ophiuchus stream is more extended and hencedynamically older than previously thought, easing the stellar populationversus dynamical age tension.
KW - Galaxy: halo
KW - Galaxy: kinematics and dynamics
KW - Galaxy: structure
KW - globular clusters: general
U2 - 10.3847/2041-8205/816/1/L4
DO - 10.3847/2041-8205/816/1/L4
M3 - Article
SN - 2041-8205
VL - 816
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1
ER -