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Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-Faint Satellites Grus II, Tucana IV, and Tucana V | | J. D. Simon
; T. S. Li
; D. Erkal
; A. B. Pace
; A. Drlica-Wagner
; D. J. James
; J. L. Marshall
; K. Bechtol
; T. Hansen
; K. Kuehn
; C. Lidman
; S. Allam
; J. Annis
; S. Avila
; E. Bertin
; D. Brooks
; D. L. Burke
; A. Carnero Rosell
; M. Carrasco Kind
; J. Carretero
; L. N. da Costa
; J. De Vicente
; S. Desai
; P. Doel
; T. F. Eifler
; S. Everett
; P. Fosalba
; J. Frieman
; J. Garcia-Bellido
; E. Gaztanaga
; D. W. Gerdes
; D. Gruen
; R. A. Gruendl
; J. Gschwend
; G. Gutierrez
; D. L. Hollowood
; K. Honscheid
; E. Krause
; N. Kuropatkin
; N. MacCrann
; M. A. G. Maia
; M. March
; R. Miquel
; A. Palmese
; F. Paz-Chinchon
; A. A. Plazas
; K. Reil
; A. Roodman
; E. Sanchez
; B. Santiago
; V. Scarpine
; M. Schubnell
; S. Serrano
; M. Smith
; E. Suchyta
; G. Tarle
; A. R. Walker
; | | Date: |
19 Nov 2019 | | Abstract: | We present Magellan/IMACS spectroscopy of three recently discovered
ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We measure
systemic velocities of V_hel = -110.0 +/- 0.5 km/s, V_hel = 15.9 +/- 1.8 km/s,
and V_hel = -36.2 +/-2.5 km/s for the three objects, respectively. Their large
relative velocity differences demonstrate that the satellites are unrelated
despite their close physical proximity to one another. We determine a velocity
dispersion for Tuc IV of sigma = 4.3^+1.7_-1.0 km/s, but are unable to resolve
the velocity dispersions of the other two systems. For Gru II we place an upper
limit at 90% confidence on the dispersion of sigma < 1.9 km/s, and for Tuc V we
are not able to obtain any useful limits. All three satellites have low mean
metallicities below [Fe/H] = -2.1, but none has a detectable metallicity
spread. Using the spectroscopic member stars, we determine proper motions for
each satellite from the second Gaia data release. We compute their orbits
around the Milky Way, finding that all three objects are currently approaching
pericenter. Gru II is on a tightly bound orbit with a pericentric distance of
25 kpc and apocenter of 66 kpc. Tuc V has a significantly more extended orbit,
with an apocenter likely beyond 100 kpc, and could be approaching the Milky Way
for the first time. The current orbital parameters of Tuc IV are similar to
those of Gru II, with a pericenter of 25 kpc. However, a backward integration
of the orbit of Tuc IV demonstrates that it collided with the Large Magellanic
Cloud with an impact parameter of 4 kpc ~120 Myr ago, deflecting its trajectory
and possibly altering its internal kinematics. Based on their sizes, masses,
and metallicities, we classify Gru II and Tuc IV as likely dwarf galaxies, but
we are not able to draw strong conclusions about the nature of Tuc V. [slightly
abridged] | | Source: | arXiv, 1911.8493 | | Services: | Forum | Review | PDF | Favorites | |
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