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Title: Portrait of a dark horse: a photometric and spectroscopic study of the ultra-faint Milky Way satellite Pegasus III

Abstract

Pegasus III (Peg III) is one of the few known ultra-faint stellar systems in the outer halo of the Milky Way. We present the results from a follow-up campaign with Magellan/IMACS and Keck/DEIMOS. Deep stellar photometry down to r{sub 0}≈25 mag at 50% completeness level has allowed accurate measurements of its photometric and structural properties. The color–magnitude diagram of Peg III confirms that the stellar system is well described by an old (≳12 Gyr) and metal-poor ([Fe/H] ≲ −2.0 dex) stellar population at a heliocentric distance of 215 ± 12 kpc. The revised half-light radius r{sub h}=53±14 pc, ellipticity ϵ=0.38{sub −0.38}{sup +0.22}, and total luminosity M{sub V}=−3.4±0.4 are in good agreement with the values quoted in our previous paper. We further report on the spectroscopic identification of seven, possibly eight, member stars of Peg III. The Ca ii triplet lines of the brightest member stars indicate that Peg III contains stars with metallicity as low as [Fe/H] = −2.55 ± 0.15 dex. Peg III has a systemic velocity of −222.9 ± 2.6 km s{sup −1} and a velocity dispersion of 5.4{sub −2.5}{sup +3.0} km s{sup −1}. The inferred dynamical mass within the half-light radius is 1.4{sub −1.1}{sup +3.0}×10{sup 6}M{sub ⊙} and the mass-to-light ratio M/L{sub V}=1470{sub −1240}{sup +5660} M{sub ⊙}/L{submore » ⊙}, providing further evidence that Peg III is a dwarf galaxy satellite. We find that Peg III and another distant dwarf satellite Pisces II lie relatively close to each other (Δd{sub spatial}=43±19 kpc) and share similar radial velocities in the Galactic standard-of-rest frame (Δv{sub GSR}=12.3±3.7 km s{sup −1}). This suggests that they may share a common origin.« less

Authors:
; ; ; ; ;  [1];  [2]; ;  [3]
  1. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia)
  2. Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06510 (United States)
  3. Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
Publication Date:
OSTI Identifier:
22868381
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 833; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DISPERSIONS; DISTANCE; LUMINOSITY; MASS; METALLICITY; MILKY WAY; PHOTOMETRY; RADIAL VELOCITY; SATELLITES; STARS

Citation Formats

Kim, Dongwon, Jerjen, Helmut, Milone, Antonino P., Costa, Gary Da, Mackey, Dougal, Conn, Blair, Geha, Marla, Chiti, Anirudh, and Frebel, Anna. Portrait of a dark horse: a photometric and spectroscopic study of the ultra-faint Milky Way satellite Pegasus III. United States: N. p., 2016. Web. doi:10.3847/0004-637X/833/1/16.
Kim, Dongwon, Jerjen, Helmut, Milone, Antonino P., Costa, Gary Da, Mackey, Dougal, Conn, Blair, Geha, Marla, Chiti, Anirudh, & Frebel, Anna. Portrait of a dark horse: a photometric and spectroscopic study of the ultra-faint Milky Way satellite Pegasus III. United States. https://doi.org/10.3847/0004-637X/833/1/16
Kim, Dongwon, Jerjen, Helmut, Milone, Antonino P., Costa, Gary Da, Mackey, Dougal, Conn, Blair, Geha, Marla, Chiti, Anirudh, and Frebel, Anna. Sat . "Portrait of a dark horse: a photometric and spectroscopic study of the ultra-faint Milky Way satellite Pegasus III". United States. https://doi.org/10.3847/0004-637X/833/1/16.
@article{osti_22868381,
title = {Portrait of a dark horse: a photometric and spectroscopic study of the ultra-faint Milky Way satellite Pegasus III},
author = {Kim, Dongwon and Jerjen, Helmut and Milone, Antonino P. and Costa, Gary Da and Mackey, Dougal and Conn, Blair and Geha, Marla and Chiti, Anirudh and Frebel, Anna},
abstractNote = {Pegasus III (Peg III) is one of the few known ultra-faint stellar systems in the outer halo of the Milky Way. We present the results from a follow-up campaign with Magellan/IMACS and Keck/DEIMOS. Deep stellar photometry down to r{sub 0}≈25 mag at 50% completeness level has allowed accurate measurements of its photometric and structural properties. The color–magnitude diagram of Peg III confirms that the stellar system is well described by an old (≳12 Gyr) and metal-poor ([Fe/H] ≲ −2.0 dex) stellar population at a heliocentric distance of 215 ± 12 kpc. The revised half-light radius r{sub h}=53±14 pc, ellipticity ϵ=0.38{sub −0.38}{sup +0.22}, and total luminosity M{sub V}=−3.4±0.4 are in good agreement with the values quoted in our previous paper. We further report on the spectroscopic identification of seven, possibly eight, member stars of Peg III. The Ca ii triplet lines of the brightest member stars indicate that Peg III contains stars with metallicity as low as [Fe/H] = −2.55 ± 0.15 dex. Peg III has a systemic velocity of −222.9 ± 2.6 km s{sup −1} and a velocity dispersion of 5.4{sub −2.5}{sup +3.0} km s{sup −1}. The inferred dynamical mass within the half-light radius is 1.4{sub −1.1}{sup +3.0}×10{sup 6}M{sub ⊙} and the mass-to-light ratio M/L{sub V}=1470{sub −1240}{sup +5660} M{sub ⊙}/L{sub ⊙}, providing further evidence that Peg III is a dwarf galaxy satellite. We find that Peg III and another distant dwarf satellite Pisces II lie relatively close to each other (Δd{sub spatial}=43±19 kpc) and share similar radial velocities in the Galactic standard-of-rest frame (Δv{sub GSR}=12.3±3.7 km s{sup −1}). This suggests that they may share a common origin.},
doi = {10.3847/0004-637X/833/1/16},
url = {https://www.osti.gov/biblio/22868381}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 833,
place = {United States},
year = {2016},
month = {12}
}