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Title: Farthest neighbor: The distant Milky Way satellite Eridanus II

Abstract

We present Magellan/IMACS spectroscopy of the recently-discovered Milky Way satellite Eridanus II (Eri II). We identify 28 member stars in Eri II, from which we measure a systemic radial velocity of $$v_{\rm hel} = 75.6 \pm 1.3~\mbox{(stat.)} \pm 2.0~\mbox{(sys.)}~\mathrm{km\,s^{-1}}$$ and a velocity dispersion of $$6.9^{+1.2}_{-0.9}~\mathrm{km\,s^{-1}}$$. Assuming that Eri~II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of Eri II is $$1.2^{+0.4}_{-0.3} \times 10^{7}~\mathrm{M_\odot}$$, indicating a mass-to-light ratio of $$420^{+210}_{-140}~\mathrm{M_\odot}/\mathrm{L_\odot}$$ and confirming that it is a dark matter-dominated dwarf galaxy. From the equivalent width measurements of the CaT lines of 16 red giant member stars, we derive a mean metallicity of $${\rm [Fe/H]} = -2.38 \pm 0.13$$ and a metallicity dispersion of $$\sigma_{\rm [Fe/H]} = 0.47 ^{+0.12}_{-0.09}$$. The velocity of Eri II in the Galactic Standard of Rest frame is $$v_{\rm GSR} = -66.6~\mathrm{km\,s^{-1}}$$, indicating that either Eri II is falling into the Milky Way potential for the first time or it has passed the apocenter of its orbit on a subsequent passage. At a Galactocentric distance of $$\sim$$370 kpc, Eri II is one of the Milky Way's most distant satellites known. Additionally, we show that the bright blue stars previously suggested to bemore » a young stellar population are not associated with Eri II. The lack of gas and recent star formation in Eri II is surprising given its mass and distance from the Milky Way, and may place constraints on models of quenching in dwarf galaxies and on the distribution of hot gas in the Milky Way halo. Furthermore, the large velocity dispersion of Eri II can be combined with the existence of a central star cluster to constrain MACHO dark matter with mass $$\gtrsim10~\mathrm{M_\odot}$$.« less

Authors:
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Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP)
Contributing Org.:
DES Collaboration
OSTI Identifier:
1349627
Alternate Identifier(s):
OSTI ID: 1345629; OSTI ID: 1368580
Report Number(s):
FERMILAB-PUB-16-479-AE-PPD; arXiv:1611.05052
Journal ID: ISSN 1538-4357; KJ0402000; KJ0503000; ERKJ311; ERKJEPM; TRN: US1700601
Grant/Contract Number:  
AC05-00OR22725; AC02-07CH11359; AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Volume: 838; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; dark matter; galaxies: dwarf; galaxies: individual (Eridanus II); galaxies: stellar content; Local Group; stars: abundances

Citation Formats

Li, T. S., Simon, J. D., Drlica-Wagner, A., Bechtol, K., Wang, M. Y., García-Bellido, J., Frieman, J., Marshall, J. L., James, D. J., Strigari, L., Pace, A. B., Balbinot, E., Zhang, Y., Abbott, T. M. C., Allam, S., Benoit-Lévy, A., Bernstein, G. M., Bertin, E., Brooks, D., Burke, D. L., Rosell, A. Carnero, Kind, M. Carrasco, Carretero, J., Cunha, C. E., D’Andrea, C. B., Costa, L. N. da, DePoy, D. L., Desai, S., Diehl, H. T., Eifler, T. F., Flaugher, B., Goldstein, D. A., Gruen, D., Gruendl, R. A., Gschwend, J., Gutierrez, G., Krause, E., Kuehn, K., Lin, H., Maia, M. A. G., March, M., Menanteau, F., Miquel, R., Plazas, A. A., Romer, A. K., Sanchez, E., Santiago, B., Schubnell, M., Sevilla-Noarbe, I., Smith, R. C., Sobreira, F., Suchyta, E., Tarle, G., Thomas, D., Tucker, D. L., Walker, A. R., Wechsler, R. H., Wester, W., and Yanny, B. Farthest neighbor: The distant Milky Way satellite Eridanus II. United States: N. p., 2017. Web. doi:10.3847/1538-4357/aa6113.
Li, T. S., Simon, J. D., Drlica-Wagner, A., Bechtol, K., Wang, M. Y., García-Bellido, J., Frieman, J., Marshall, J. L., James, D. J., Strigari, L., Pace, A. B., Balbinot, E., Zhang, Y., Abbott, T. M. C., Allam, S., Benoit-Lévy, A., Bernstein, G. M., Bertin, E., Brooks, D., Burke, D. L., Rosell, A. Carnero, Kind, M. Carrasco, Carretero, J., Cunha, C. E., D’Andrea, C. B., Costa, L. N. da, DePoy, D. L., Desai, S., Diehl, H. T., Eifler, T. F., Flaugher, B., Goldstein, D. A., Gruen, D., Gruendl, R. A., Gschwend, J., Gutierrez, G., Krause, E., Kuehn, K., Lin, H., Maia, M. A. G., March, M., Menanteau, F., Miquel, R., Plazas, A. A., Romer, A. K., Sanchez, E., Santiago, B., Schubnell, M., Sevilla-Noarbe, I., Smith, R. C., Sobreira, F., Suchyta, E., Tarle, G., Thomas, D., Tucker, D. L., Walker, A. R., Wechsler, R. H., Wester, W., & Yanny, B. Farthest neighbor: The distant Milky Way satellite Eridanus II. United States. https://doi.org/10.3847/1538-4357/aa6113
Li, T. S., Simon, J. D., Drlica-Wagner, A., Bechtol, K., Wang, M. Y., García-Bellido, J., Frieman, J., Marshall, J. L., James, D. J., Strigari, L., Pace, A. B., Balbinot, E., Zhang, Y., Abbott, T. M. C., Allam, S., Benoit-Lévy, A., Bernstein, G. M., Bertin, E., Brooks, D., Burke, D. L., Rosell, A. Carnero, Kind, M. Carrasco, Carretero, J., Cunha, C. E., D’Andrea, C. B., Costa, L. N. da, DePoy, D. L., Desai, S., Diehl, H. T., Eifler, T. F., Flaugher, B., Goldstein, D. A., Gruen, D., Gruendl, R. A., Gschwend, J., Gutierrez, G., Krause, E., Kuehn, K., Lin, H., Maia, M. A. G., March, M., Menanteau, F., Miquel, R., Plazas, A. A., Romer, A. K., Sanchez, E., Santiago, B., Schubnell, M., Sevilla-Noarbe, I., Smith, R. C., Sobreira, F., Suchyta, E., Tarle, G., Thomas, D., Tucker, D. L., Walker, A. R., Wechsler, R. H., Wester, W., and Yanny, B. Fri . "Farthest neighbor: The distant Milky Way satellite Eridanus II". United States. https://doi.org/10.3847/1538-4357/aa6113. https://www.osti.gov/servlets/purl/1349627.
@article{osti_1349627,
title = {Farthest neighbor: The distant Milky Way satellite Eridanus II},
author = {Li, T. S. and Simon, J. D. and Drlica-Wagner, A. and Bechtol, K. and Wang, M. Y. and García-Bellido, J. and Frieman, J. and Marshall, J. L. and James, D. J. and Strigari, L. and Pace, A. B. and Balbinot, E. and Zhang, Y. and Abbott, T. M. C. and Allam, S. and Benoit-Lévy, A. and Bernstein, G. M. and Bertin, E. and Brooks, D. and Burke, D. L. and Rosell, A. Carnero and Kind, M. Carrasco and Carretero, J. and Cunha, C. E. and D’Andrea, C. B. and Costa, L. N. da and DePoy, D. L. and Desai, S. and Diehl, H. T. and Eifler, T. F. and Flaugher, B. and Goldstein, D. A. and Gruen, D. and Gruendl, R. A. and Gschwend, J. and Gutierrez, G. and Krause, E. and Kuehn, K. and Lin, H. and Maia, M. A. G. and March, M. and Menanteau, F. and Miquel, R. and Plazas, A. A. and Romer, A. K. and Sanchez, E. and Santiago, B. and Schubnell, M. and Sevilla-Noarbe, I. and Smith, R. C. and Sobreira, F. and Suchyta, E. and Tarle, G. and Thomas, D. and Tucker, D. L. and Walker, A. R. and Wechsler, R. H. and Wester, W. and Yanny, B.},
abstractNote = {We present Magellan/IMACS spectroscopy of the recently-discovered Milky Way satellite Eridanus II (Eri II). We identify 28 member stars in Eri II, from which we measure a systemic radial velocity of $v_{\rm hel} = 75.6 \pm 1.3~\mbox{(stat.)} \pm 2.0~\mbox{(sys.)}~\mathrm{km\,s^{-1}}$ and a velocity dispersion of $6.9^{+1.2}_{-0.9}~\mathrm{km\,s^{-1}}$. Assuming that Eri~II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of Eri II is $1.2^{+0.4}_{-0.3} \times 10^{7}~\mathrm{M_\odot}$, indicating a mass-to-light ratio of $420^{+210}_{-140}~\mathrm{M_\odot}/\mathrm{L_\odot}$ and confirming that it is a dark matter-dominated dwarf galaxy. From the equivalent width measurements of the CaT lines of 16 red giant member stars, we derive a mean metallicity of ${\rm [Fe/H]} = -2.38 \pm 0.13$ and a metallicity dispersion of $\sigma_{\rm [Fe/H]} = 0.47 ^{+0.12}_{-0.09}$. The velocity of Eri II in the Galactic Standard of Rest frame is $v_{\rm GSR} = -66.6~\mathrm{km\,s^{-1}}$, indicating that either Eri II is falling into the Milky Way potential for the first time or it has passed the apocenter of its orbit on a subsequent passage. At a Galactocentric distance of $\sim$370 kpc, Eri II is one of the Milky Way's most distant satellites known. Additionally, we show that the bright blue stars previously suggested to be a young stellar population are not associated with Eri II. The lack of gas and recent star formation in Eri II is surprising given its mass and distance from the Milky Way, and may place constraints on models of quenching in dwarf galaxies and on the distribution of hot gas in the Milky Way halo. Furthermore, the large velocity dispersion of Eri II can be combined with the existence of a central star cluster to constrain MACHO dark matter with mass $\gtrsim10~\mathrm{M_\odot}$.},
doi = {10.3847/1538-4357/aa6113},
url = {https://www.osti.gov/biblio/1349627}, journal = {The Astrophysical Journal (Online)},
issn = {1538-4357},
number = 1,
volume = 838,
place = {United States},
year = {2017},
month = {3}
}

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Works referenced in this record:

Observation of Gravitational Waves from a Binary Black Hole Merger
journal, February 2016


Dwarf Galaxy dark Matter Density Profiles Inferred from Stellar and gas Kinematics
journal, June 2014


MACHO Project Limits on Black Hole Dark Matter in the 1–30 [ITAL]M[/ITAL][TINF]⊙[/TINF] Range
journal, April 2001


Astropy: A community Python package for astronomy
journal, September 2013


Pre-launch estimates for GLAST sensitivity to dark matter annihilation signals
journal, July 2008


The H I Parkes All Sky Survey: southern observations, calibration and robust imaging
journal, April 2001


Eight new Milky way Companions Discovered in First-Year dark Energy Survey data
journal, June 2015


Observable monochromatic photons from cosmic photino annihilation
journal, June 1988


Did LIGO Detect Dark Matter?
journal, May 2016


The Galaxy in Context: Structural, Kinematic, and Integrated Properties
journal, September 2016


Gas‐Rich Dwarf Spheroidals
journal, October 2000


THE MILKY WAY'S CIRCULAR-VELOCITY CURVE BETWEEN 4 AND 14 kpc FROM APOGEE DATA
journal, October 2012


parsec : stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
journal, October 2012


The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization era
journal, November 2014


The Parkes H I Survey of the Magellanic System
journal, February 2005


Hierarchical Galaxy Formation and Substructure in the Galaxy’s Stellar Halo
journal, February 2001


The near-infrared Ca ii triplet as a metallicity indicator – II. Extension to extremely metal-poor metallicity regimes★
journal, July 2013


Massive primordial black holes from hybrid inflation as dark matter and the seeds of galaxies
journal, July 2015


The mass distribution of the Fornax dSph: constraints from its globular cluster distribution: The mass distribution of the Fornax dSph
journal, September 2012


Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V
journal, January 2017


Deep Imaging of Eridanus ii and its lone star Cluster
journal, June 2016


Mass Density Profiles of Low Surface Brightness Galaxies
journal, May 2001


The Structural Properties and Star Formation History of Leo T from Deep LBT Photometry
journal, June 2008


The dependence of dark matter profiles on the stellar-to-halo mass ratio: a prediction for cusps versus cores
journal, November 2013


IMACS: The Inamori-Magellan Areal Camera and Spectrograph on Magellan-Baade
journal, March 2011

  • Dressler, Alan; Bigelow, Bruce; Hare, Tyson
  • Publications of the Astronomical Society of the Pacific, Vol. 123, Issue 901
  • https://doi.org/10.1086/658908

IMACS: the wide-field imaging spectrograph on Magellan-Baade
conference, June 2006


SEARCH FOR GAMMA-RAY EMISSION FROM DES DWARF SPHEROIDAL GALAXY CANDIDATES WITH FERMI -LAT DATA
journal, August 2015


An Ultra-Faint Galaxy Candidate Discovered in Early data from the Magellanic Satellites Survey
journal, November 2016


Eight Ultra-Faint Galaxy Candidates Discovered in year two of the dark Energy Survey
journal, November 2015


The structure of cold dark matter halos
journal, September 1991


Missing mass around galaxies: morphological evidence
journal, November 1974


Under pressure: quenching star formation in low-mass satellite galaxies via stripping
journal, August 2016


Taking care of business in a flash : constraining the time-scale for low-mass satellite quenching with ELVIS
journal, October 2015


corner.py: Scatterplot matrices in Python
journal, June 2016


emcee : The MCMC Hammer
journal, March 2013

  • Foreman-Mackey, Daniel; Hogg, David W.; Lang, Dustin
  • Publications of the Astronomical Society of the Pacific, Vol. 125, Issue 925
  • https://doi.org/10.1086/670067

ELVIS: Exploring the Local Volume in Simulations
journal, January 2014


Dwarf Galaxy Annihilation and Decay Emission Profiles for dark Matter Experiments
journal, March 2015


Cuspy no more: how outflows affect the central dark matter and baryon distribution in Λ cold dark matter galaxies: Galaxy cores in ΛCDM
journal, March 2012


H i in Local Group Dwarf Galaxies and Stripping by the Galactic halo
journal, April 2009


Some astrophysical consequences of the existence of a heavy stable neutral lepton
journal, August 1978


A new Milky way Satellite Discovered in the Subaru/Hyper Suprime-Cam Survey
journal, November 2016


Discovery of an Unusual Dwarf Galaxy in the Outskirts of the Milky Way
journal, January 2007


Horologium ii: a Second Ultra-Faint Milky way Satellite in the Horologium Constellation
journal, July 2015


A Hero’S dark Horse: Discovery of an Ultra-Faint Milky way Satellite in Pegasus
journal, May 2015


Discovery of a Faint Outer halo Milky way star Cluster in the Southern sky
journal, April 2015


The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies
journal, November 2013


SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE ( WMAP ) OBSERVATIONS: COSMOLOGICAL INTERPRETATION
journal, January 2011


Beasts of the Southern Wild: Discovery of nine Ultra Faint Satellites in the Vicinity of the Magellanic Clouds
journal, May 2015


Did massive black holes in globular clusters initially satisfy galactic scaling relations?
journal, July 2013


SAGITTARIUS II, DRACO II AND LAEVENS 3: THREE NEW MILKY WAY SATELLITES DISCOVERED IN THE PAN-STARRS 1 3 π SURVEY
journal, October 2015


A NEW FAINT MILKY WAY SATELLITE DISCOVERED IN THE PAN-STARRS1 3 π SURVEY
journal, March 2015


The Hercules Satellite: a Stellar Stream in the Milky way Halo?
journal, September 2010


Hydra ii: a Faint and Compact Milky way Dwarf Galaxy Found in the Survey of the Magellanic Stellar History
journal, April 2015


A robust determination of Milky Way satellite properties using hierarchical mass modelling
journal, June 2015


The Observed Properties of Dwarf Galaxies in and Around the Local Group
journal, June 2012


Revisiting the Influence of Unidentified Binaries on Velocity Dispersion Measurements in Ultra-Faint Stellar Systems
journal, October 2010


Correcting Velocity Dispersions of Dwarf Spheroidal Galaxies for Binary Orbital Motion
journal, September 2010


The Structure of Cold Dark Matter Halos
journal, May 1996


How supernova feedback turns dark matter cusps into cores: Supernova feedback and dark matter cores
journal, March 2012


On the reported death of the MACHO era
journal, June 2009


Late gas accretion on to primordial minihaloes: a model for Leo T, dark galaxies and extragalactic high-velocity clouds
journal, January 2009


A synthetic view on structure and evolution of the Milky Way
journal, October 2003


The Local Group dwarf Leo T: H i on the brink of star formation: H i in Leo T
journal, January 2008


The Near‐Infrared Na i Doublet Feature in M Stars
journal, April 1997


Local kinematics and the local standard of rest
journal, April 2010


Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum ii
journal, July 2015


The Kinematics of the Ultra‐faint Milky Way Satellites: Solving the Missing Satellite Problem
journal, November 2007


A Complete Spectroscopic Survey of the Milky way Satellite Segue 1: the Darkest Galaxy
journal, May 2011


Exploring Halo Substructure with Giant Stars. X. Extended Dark Matter or Tidal Disruption?: The Case for the Leo I Dwarf Spheroidal Galaxy
journal, July 2007


The Dearth of Neutral Hydrogen in Galactic Dwarf Spheroidal Galaxies
journal, October 2014


A New Look at the Kinematics of Neutral Hydrogen in the Small Magellanic Cloud
journal, March 2004


The Most Dark‐Matter–dominated Galaxies: Predicted Gamma‐Ray Signals from the Faintest Milky Way Dwarfs
journal, May 2008


The mass profile of the Milky Way to the virial radius from the Illustris simulation
journal, June 2016


Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds
journal, April 2007


The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater
journal, April 2016


At the survey limits: discovery of the Aquarius 2 dwarf galaxy in the VST ATLAS and the SDSS data
journal, August 2016


New Understanding of Large Magellanic Cloud Structure, Dynamics, and Orbit from Carbon Star Kinematics
journal, November 2002


Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy
journal, April 2006


A Method for Measuring (Slopes of) the mass Profiles of Dwarf Spheroidal Galaxies
journal, November 2011


THE STAR FORMATION HISTORIES OF LOCAL GROUP DWARF GALAXIES. I. HUBBLE SPACE TELESCOPE /WIDE FIELD PLANETARY CAMERA 2 OBSERVATIONS
journal, June 2014


THE STAR FORMATION HISTORY OF LEO T FROM HUBBLE SPACE TELESCOPE IMAGING
journal, March 2012


On the neutral gas content of nine new Milky Way satellite galaxy candidates
journal, August 2015


Rapid Environmental Quenching of Satellite Dwarf Galaxies in the Local Group
journal, July 2015


Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites
journal, August 2015


Synthesis of RKA 182
journal, October 2010


    Works referencing / citing this record:

    Gaia DR 2 and VLT/FLAMES search for new satellites of the LMC
    journal, March 2019


    Scaling relations for dark matter annihilation and decay profiles in dwarf spheroidal galaxies
    journal, October 2018


    Gaia DR 2 and VLT/FLAMES search for new satellites of the LMC
    journal, March 2019


    Scaling relations for dark matter annihilation and decay profiles in dwarf spheroidal galaxies
    journal, October 2018


    Lower bound on the primordial black hole merger rate
    journal, February 2020


    On the merger rate of primordial black holes: effects of nearest neighbours distribution and clustering
    journal, October 2018


    Improved constraints from ultra-faint dwarf galaxies on primordial black holes as dark matter
    journal, January 2020


    Extending the globular cluster system–halo mass relation to the lowest galaxy masses
    journal, September 2018


    The suppression of star formation on the smallest scales: what role does environment play?
    journal, December 2018


    Tidal stripping and the structure of dwarf galaxies in the Local Group
    journal, February 2018


    The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
    journal, June 2019


    Too big to fail in light of Gaia
    journal, September 2019


    The southern stellar stream spectroscopic survey (S5): Overview, target selection, data reduction, validation, and early science
    journal, October 2019


    The effect of fluctuating fuzzy axion haloes on stellar dynamics: a stochastic model
    journal, December 2019


    Signatures of Higgs dilaton and critical Higgs inflation
    journal, January 2018


    Constraining the primordial black hole abundance with 21-cm cosmology
    journal, August 2019


    Small-scale structure of primordial black hole dark matter and its implications for accretion
    journal, October 2019


    CMB bounds on disk-accreting massive primordial black holes
    journal, October 2017


    Merger rate of primordial black-hole binaries
    journal, December 2017


    Searching for Primordial Black Holes in the Radio and X-Ray Sky
    journal, June 2017


    Dynamics of Dwarf Galaxies Disfavor Stellar-Mass Black Holes as Dark Matter
    journal, July 2017


    Strong Constraints on Fuzzy Dark Matter from Ultrafaint Dwarf Galaxy Eridanus II
    journal, July 2019


    Evidence of a Non-universal Stellar Initial Mass Function. Insights from HST Optical Imaging of Six Ultra-faint Dwarf Milky Way Satellites
    journal, February 2018


    The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-faint Galaxies
    journal, October 2018


    Proper Motions of Milky Way Ultra-faint Satellites with Gaia DR2 × DES DR1
    journal, April 2019


    Dynamical Histories of the Crater II and Hercules Dwarf Galaxies
    journal, September 2019