A Hero's Dark Horse: Discovery of an Ultra-faint Milky Way Satellite in Pegasus

Dongwon Kim; Helmut Jerjen; Dougal Mackey; Gary S. Da Costa; Antonino P. Milone

doi:10.1088/2041-8205/804/2/L44

A Hero's Dark Horse: Discovery of an Ultra-faint Milky Way Satellite in Pegasus

Dongwon Kim, Helmut Jerjen, Dougal Mackey, Gary S. Da Costa, Antonino P. Milone

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Abstract

We report the discovery of an ultra-faint Milky Way satellite galaxy in the constellation of Pegasus. The concentration of stars was detected by applying our overdensity detection algorithm to the SDSS-DR 10 and confirmed with deeper photometry from the Dark Energy Camera at the 4 m Blanco telescope. Fitting model isochrones indicates that this object, Pegasus III, features an old and metal-poor stellar population ([Fe/H] ∼ -2.1) at a heliocentric distance of 205 ± 20 kpc. The new stellar system has an estimated half-light radius of r_h = 78_-24⁺³⁰ pc and a total luminosity of M_v ∼ -4.1 ± 0.5 that places it into the domain of dwarf galaxies on the size-luminosity plane. Pegasus III is spatially close to the MW satellite Pisces II. It is possible that the two might be physically associated, similar to the Leo IV and Leo V pair. Pegasus III is also well aligned with the Vast Polar Structure, which suggests a possible physical association.

Original language	English
Article number	L44
Journal	Astrophysical Journal Letters
Volume	804
Issue number	2
DOIs	https://doi.org/10.1088/2041-8205/804/2/L44
Publication status	Published - 10 May 2015

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title = "A Hero's Dark Horse: Discovery of an Ultra-faint Milky Way Satellite in Pegasus",

abstract = "We report the discovery of an ultra-faint Milky Way satellite galaxy in the constellation of Pegasus. The concentration of stars was detected by applying our overdensity detection algorithm to the SDSS-DR 10 and confirmed with deeper photometry from the Dark Energy Camera at the 4 m Blanco telescope. Fitting model isochrones indicates that this object, Pegasus III, features an old and metal-poor stellar population ([Fe/H] ∼ -2.1) at a heliocentric distance of 205 ± 20 kpc. The new stellar system has an estimated half-light radius of rh = 78-24+30 pc and a total luminosity of Mv ∼ -4.1 ± 0.5 that places it into the domain of dwarf galaxies on the size-luminosity plane. Pegasus III is spatially close to the MW satellite Pisces II. It is possible that the two might be physically associated, similar to the Leo IV and Leo V pair. Pegasus III is also well aligned with the Vast Polar Structure, which suggests a possible physical association.",

keywords = "Galaxy: halo, Local Group, galaxies: dwarf, galaxies: individual (Pegasus III), galaxies: stellar content",

author = "Dongwon Kim and Helmut Jerjen and Dougal Mackey and {Da Costa}, {Gary S.} and Milone, {Antonino P.}",

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AU - Kim, Dongwon

AU - Jerjen, Helmut

AU - Mackey, Dougal

AU - Da Costa, Gary S.

AU - Milone, Antonino P.

PY - 2015/5/10

Y1 - 2015/5/10

N2 - We report the discovery of an ultra-faint Milky Way satellite galaxy in the constellation of Pegasus. The concentration of stars was detected by applying our overdensity detection algorithm to the SDSS-DR 10 and confirmed with deeper photometry from the Dark Energy Camera at the 4 m Blanco telescope. Fitting model isochrones indicates that this object, Pegasus III, features an old and metal-poor stellar population ([Fe/H] ∼ -2.1) at a heliocentric distance of 205 ± 20 kpc. The new stellar system has an estimated half-light radius of rh = 78-24+30 pc and a total luminosity of Mv ∼ -4.1 ± 0.5 that places it into the domain of dwarf galaxies on the size-luminosity plane. Pegasus III is spatially close to the MW satellite Pisces II. It is possible that the two might be physically associated, similar to the Leo IV and Leo V pair. Pegasus III is also well aligned with the Vast Polar Structure, which suggests a possible physical association.

AB - We report the discovery of an ultra-faint Milky Way satellite galaxy in the constellation of Pegasus. The concentration of stars was detected by applying our overdensity detection algorithm to the SDSS-DR 10 and confirmed with deeper photometry from the Dark Energy Camera at the 4 m Blanco telescope. Fitting model isochrones indicates that this object, Pegasus III, features an old and metal-poor stellar population ([Fe/H] ∼ -2.1) at a heliocentric distance of 205 ± 20 kpc. The new stellar system has an estimated half-light radius of rh = 78-24+30 pc and a total luminosity of Mv ∼ -4.1 ± 0.5 that places it into the domain of dwarf galaxies on the size-luminosity plane. Pegasus III is spatially close to the MW satellite Pisces II. It is possible that the two might be physically associated, similar to the Leo IV and Leo V pair. Pegasus III is also well aligned with the Vast Polar Structure, which suggests a possible physical association.

KW - Galaxy: halo

KW - Local Group

KW - galaxies: dwarf

KW - galaxies: individual (Pegasus III)

KW - galaxies: stellar content

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DO - 10.1088/2041-8205/804/2/L44

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VL - 804

JO - Astrophysical Journal Letters

JF - Astrophysical Journal Letters

IS - 2

M1 - L44

ER -

A Hero's Dark Horse: Discovery of an Ultra-faint Milky Way Satellite in Pegasus

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