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Title: Ships Passing in the Night: Spectroscopic Analysis of Two Ultra-faint Satellites in the Constellation Carina

Journal Article · · The Astrophysical Journal (Online)
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We present Magellan/IMACS, Anglo-Australian Telescope/AAOmega+2dF, and Very Large Telescope/GIRAFFE+FLAMES spectroscopy of the Carina II (Car II) and Carina III (Car III) dwarf galaxy candidates, recently discovered in the Magellanic Satellites Survey (MagLiteS). We identify 18 member stars in Car II, including two binaries with variable radial velocities and two RR Lyrae stars. The other 14 members have a mean heliocentric velocity and a velocity dispersion of . Assuming Car II is in dynamical equilibrium, we derive a total mass within the half-light radius of , indicating a mass-to-light ratio of /. From equivalent width measurements of the calcium triplet lines of nine red giant branch (RGB) stars, we derive a mean metallicity of with dispersion . Considering both the kinematic and chemical properties, we conclude that Car II is a dark-matter-dominated dwarf galaxy. For Car III, we identify four member stars, from which we calculate a systemic velocity of . The brightest RGB member of Car III has a metallicity of . Due to the small size of the Car III spectroscopic sample, we cannot conclusively determine its nature. Although these two systems have the smallest known physical separation () among Local Group satellites, the large difference in their systemic velocities, , indicates that they are unlikely to be a bound pair. One or both systems are likely associated with the Large Magellanic Cloud (LMC), and may remain LMC satellites today. No statistically significant excess of γ-ray emission is found at the locations of Car II and Car III in eight years of Fermi-LAT data.

Research Organization:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
Sponsoring Organization:
USDOE; National Aeronautics and Space Administration (NASA)
Contributing Organization:
MagLiteS Collaboration
Grant/Contract Number:
AC02-07CH11359; AC02-76SF00515
OSTI ID:
1438564
Alternate ID(s):
OSTI ID: 1439046
Report Number(s):
arXiv:1802.06810; FERMILAB-PUB-18-110-AE-PPD; TRN: US1900464
Journal Information:
The Astrophysical Journal (Online), Vol. 857, Issue 2; ISSN 1538-4357
Publisher:
Institute of Physics (IOP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 41 works
Citation information provided by
Web of Science

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Gaia DR2 proper motions of dwarf galaxies within 420 kpc : Orbits, Milky Way mass, tidal influences, planar alignments, and group infall journal November 2018
With and without spectroscopy: Gaia DR2 proper motions of seven ultra-faint dwarf galaxies journal December 2018
Gaia DR 2 and VLT/FLAMES search for new satellites of the LMC journal March 2019
Improved constraints from ultra-faint dwarf galaxies on primordial black holes as dark matter journal January 2020
Scaling relations for dark matter annihilation and decay profiles in dwarf spheroidal galaxies journal October 2018
The suppression of star formation on the smallest scales: what role does environment play? journal December 2018
The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2 journal June 2019
The southern stellar stream spectroscopic survey (S5): Overview, target selection, data reduction, validation, and early science journal October 2019
The velocity anisotropy of the Milky Way satellite system journal April 2019
An Updated Small Magellanic Cloud and Magellanic Bridge Catalog of Star Clusters, Associations, and Related Objects journal February 2020
Gaia Proper Motions and Orbits of the Ultra-faint Milky Way Satellites journal August 2018
The First Tidally Disrupted Ultra-faint Dwarf Galaxy?: A Spectroscopic Analysis of the Tucana III Stream journal October 2018
The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-faint Galaxies journal October 2018
Exploring the Very Extended Low-surface-brightness Stellar Populations of the Large Magellanic Cloud with SMASH journal March 2019
Chemical Abundance Analysis of Tucana III, the Second r -process Enhanced Ultra-faint Dwarf Galaxy journal September 2019
Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III journal January 2020
How low does it go? Too few Galactic satellites with standard reionization quenching journal July 2019
The hidden giant: Discovery of an enormous Galactic dwarf satellite in Gaia DR2 text January 2019
Proper Motions of Milky Way Ultra-faint Satellites with Gaia DR2 × DES DR1 journal April 2019
Dancing in the Dark: Uncertainty in Ultrafaint Dwarf Galaxy Predictions from Cosmological Simulations journal March 2019
Improved constraints from ultra-faint dwarf galaxies on primordial black holes as dark matter text January 2020
The Suppression of Star Formation on the Smallest Scales: What Role Does Environment Play? text January 2018
The velocity anisotropy of the Milky Way satellite system text January 2018


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