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V. Belokurov,
M. G. Walker,
N. W. Evans,
G. Gilmore,
M. J. Irwin,
D. Just,
S. Koposov, M. Mateo,
E. Olszewski,
L. Watkins,
L. Wyrzykowski
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ABSTRACT: We report the discovery of two new Milky Way satellites in the neighboring constellations of Pisces and Pegasus identified in data from the Sloan Digital Sky Survey. Pisces II, an ultra-faint dwarf galaxy lies at the distance of ~180 kpc, some 15 degrees away from the recently detected Pisces I. Segue 3, an ultra-faint star cluster lies at the distance of 16 kpc. We use deep follow-up imaging obtained with the 4-m Mayall telescope at Kitt Peak National Observatory to derive their structural parameters. Pisces II has a half-light radius of ~60 pc, while Segue 3 is twenty times smaller at only 3pc. Comment: Accepted for publication in ApJL
02/2010;
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ABSTRACT: We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope (MMT). From this, we derive a luminosity of Mv=−2.5, a half-light radius of 34 pc and a systemic velocity of ∼−40 km s−1. Our data also provide evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighbouring fields. We resolve the velocity dispersion of Segue 2 as 3.4 km s−1 and the possible stream as ∼7 km s−1. This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites – survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts z > 10 and are good candidates for fossils of the reionization epoch.
Monthly Notices of the Royal Astronomical Society 08/2009; 397(4):1748 - 1755. · 4.90 Impact Factor
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ABSTRACT: We present a spectroscopic study of Leo V, a recently discovered satellite of the Milky Way (MW). From stellar spectra obtained with the MMT/Hectochelle spectrograph we identify seven likely members of Leo V. Five cluster near the Leo V center (R < 3') and have a velocity dispersion of 2.4+2.4 –1.4 km s–1. The other two likely members lie near each other but far from the center (R ~ 13' ~ 700 pc) and inflate the global velocity dispersion to 3.7+2.3 –1.4 km s–1. Assuming the five central members are bound, we obtain a dynamical mass of M = 3.3+9.1 –2.5 × 105 M ☉ (M/LV = 75+230 –58[M/LV ]☉). From the stacked spectrum of the five central members we estimate a mean metallicity of [Fe/H]=–2.0 ± 0.2 dex. Thus, with respect to dwarf spheroidals of similar luminosity, Leo V is slightly less massive and slightly more metal rich. Since we resolve the central velocity dispersion only marginally, we do not rule out the possibility that Leo V is a diffuse star cluster devoid of dark matter. The wide separation of its two outer members implies Leo V is losing mass; however, its large distance (D ~ 180 kpc) is difficult to reconcile with MW tidal stripping unless the orbit is very radial.
The Astrophysical Journal 03/2009; 694(2):L144. · 6.02 Impact Factor
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ABSTRACT: We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope. From this, we derive a luminosity of M_v = -2.5, a half-light radius of 34 pc and a systemic velocity of -40$ km/s. Our MMT data also provides evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighboring fields. We resolve the velocity dispersion of Segue 2 as 3.4 km/s and the possible stream as about 7 km/s. This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites -- survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts z > 10 and are good candidates for fossils of the reionization epoch. Comment: MNRAS, Submitted
03/2009;
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ABSTRACT: We report the discovery of a new Milky Way satellite in the constellation Leo, identified in data from the Sloan Digital Sky Survey. It lies at a distance of ~180 kpc, and is separated by 3° from another recent discovery, Leo IV. We present follow-up imaging from the Isaac Newton Telescope and spectroscopy from the Hectochelle fiber spectrograph at the Multiple Mirror Telescope. Leo V's heliocentric velocity is ~173.3 ± 3.1 km s−1, offset by ~40 km s−1 from that of Leo IV. A simple interpretation of the kinematic data is that both objects may lie on the same stream, although the implied orbit is only modestly eccentric (e ~ 0.2)
The Astrophysical Journal 12/2008; 686(2):L83. · 6.02 Impact Factor
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ABSTRACT: We report the discovery of a new Milky Way dwarf spheroidal galaxy in the constellation of Leo identified in data from the Sloan Digital Sky Survey. Leo V lies at a distance of about 180 kpc, and is separated by about 3 degrees from another recent discovery, Leo IV. We present follow-up imaging from the Isaac Newton Telescope and spectroscopy from the Hectochelle fiber spectrograph at the Multiple Mirror Telescope. Leo V's heliocentric velocity is 173.4 km/s, which is offset by about 40 km/s from that of Leo IV. A simple interpretation of the kinematic data is that both objects may lie on the same stream, though the implied orbit is only modestly eccentric (e = 0.2)
08/2008;
