AustralieFrV1, PascalFrancis, Corpus, bibRecord, 003A10

A Keck/DEIMOS spectroscopic survey of faint Galactic satellites : searching for the least massive dwarf galaxies

Identifieur interne : 003A10 ( PascalFrancis/Corpus ); précédent : 003A09; suivant : 003A11

A Keck/DEIMOS spectroscopic survey of faint Galactic satellites : searching for the least massive dwarf galaxies

Auteurs : N. F. Martin ; R. A. Ibata ; S. C. Chapman ; M. Irwin ; G. F. Lewis

Source :

Monthly Notices of the Royal Astronomical Society [ 0035-8711 ] ; 2007.

RBID : Pascal:07-0409359

Descripteurs français

Pascal (Inist)
- Deimos, Galaxies naines, Voie lactée, Vitesse radiale, Rapport signal bruit, Métallicité, Dispersion vitesse, Matière sombre, Amas globulaire, Rapport masse luminosité, Galaxies compagnons, Groupe local, Cinématique, Dynamique, Satellite Mars, Amas stellaire, Interaction tidale.

English descriptors

KwdEn :
- Dark matter, Deimos, Dwarf galaxies, Dynamics, Globular clusters, Kinematics, Local group, Mars satellite, Mass to light ratio, Metallicity, Milky Way, Radial velocity, Satellite galaxies, Signal-to-noise ratio, Star clusters, Tidal interaction, Velocity dispersion.

Abstract

We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Bootes, Ursa Major I, Ursa Major II and Willman 1 (Will). Using the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, we have obtained samples that contain from ∼ 15 to ∼85 probable members of these satellites for which we derive radial velocities precise to a few km s^-1 down to i ∼ 21-22. About half of these stars are observed with a high enough signal-to-noise ratio to estimate their metallicity to within ±0.2 dex. The characteristics of all the observed stars are made available, along with those of the Canes Venatici I dwarf galaxy that have been analysed in a companion paper. From this data set, we show that Ursa Major II is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (ù_r = 115 ± 5kms^-1) is in good agreement with simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark matter dominated systems (under the usual assumptions of symmetry and virial equilibrium). In particular, we show that despite its small size and faintness, the Will object is not a globular cluster given its metallicity scatter over -2.0 ≤ [Fe/H] ≤ -1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3 +2.3-1.3 km s^-1 around a systemic velocity of -12.3 ± 2.3 km s^-1 which implies a mass-to-light ratio of ∼700 and a total mass of ∼5 x 10⁵ M_O for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 10⁷ M_O limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modelling and an extended search for potential extratidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.

Notice en format standard (ISO 2709)

Pour connaître la documentation sur le format Inist Standard.

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A08	`01`	`1`	`ENG`	`@1 A Keck/DEIMOS spectroscopic survey of faint Galactic satellites : searching for the least massive dwarf galaxies`
A11	`01`	`1`		`@1 MARTIN (N. F.)`
A11	`02`	`1`		`@1 IBATA (R. A.)`
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A11	`04`	`1`		`@1 IRWIN (M.)`
A11	`05`	`1`		`@1 LEWIS (G. F.)`
A14	`01`			`@1 Max-Planck-Institut für Astronomie, Königstuhl 17 @2 69117 Heidelberg @3 DEU @Z 1 aut.`
A14	`02`			`@1 Observatoire de Strasbourg, 11, rue de l'Université @2 67000 Strasbourg @3 FRA @Z 2 aut.`
A14	`03`			`@1 Institute of Astronomy, Madingley Road @2 Cambridge CB3 0HA @3 GBR @Z 3 aut. @Z 4 aut.`
A14	`04`			`@1 Department of Physics and Astronomy, University of Victoria @2 Victoria, BC, V8P 1A1 @3 CAN @Z 3 aut.`
A14	`05`			`@1 Institute of Astronomy, School of Physics, A29 University of Sydney @2 NSW 2006 @3 AUS @Z 5 aut.`
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A44				`@0 0000 @1 © 2007 INIST-CNRS. All rights reserved.`
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C01	`01`		`ENG`	@0 We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Bootes, Ursa Major I, Ursa Major II and Willman 1 (Will). Using the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, we have obtained samples that contain from ∼ 15 to ∼85 probable members of these satellites for which we derive radial velocities precise to a few km s^-1 down to i ∼ 21-22. About half of these stars are observed with a high enough signal-to-noise ratio to estimate their metallicity to within ±0.2 dex. The characteristics of all the observed stars are made available, along with those of the Canes Venatici I dwarf galaxy that have been analysed in a companion paper. From this data set, we show that Ursa Major II is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (ù_r = 115 ± 5kms^-1) is in good agreement with simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark matter dominated systems (under the usual assumptions of symmetry and virial equilibrium). In particular, we show that despite its small size and faintness, the Will object is not a globular cluster given its metallicity scatter over -2.0 ≤ [Fe/H] ≤ -1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3 +2.3-1.3 km s^-1 around a systemic velocity of -12.3 ± 2.3 km s^-1 which implies a mass-to-light ratio of ∼700 and a total mass of ∼5 x 10⁵ M_O for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 10⁷ M_O limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modelling and an extended search for potential extratidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.
C02	`01`	`3`		`@0 001E03`
C03	`01`	`3`	`FRE`	`@0 Deimos @5 26`
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C03	`02`	`3`	`FRE`	`@0 Galaxies naines @5 27`
C03	`02`	`3`	`ENG`	`@0 Dwarf galaxies @5 27`
C03	`03`	`3`	`FRE`	`@0 Voie lactée @5 28`
C03	`03`	`3`	`ENG`	`@0 Milky Way @5 28`
C03	`04`	`3`	`FRE`	`@0 Vitesse radiale @5 29`
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C03	`05`	`3`	`FRE`	`@0 Rapport signal bruit @5 30`
C03	`05`	`3`	`ENG`	`@0 Signal-to-noise ratio @5 30`
C03	`06`	`X`	`FRE`	`@0 Métallicité @5 31`
C03	`06`	`X`	`ENG`	`@0 Metallicity @5 31`
C03	`06`	`X`	`SPA`	`@0 Metalicidad @5 31`
C03	`07`	`X`	`FRE`	`@0 Dispersion vitesse @5 32`
C03	`07`	`X`	`ENG`	`@0 Velocity dispersion @5 32`
C03	`07`	`X`	`SPA`	`@0 Dispersión velocidad @5 32`
C03	`08`	`3`	`FRE`	`@0 Matière sombre @5 33`
C03	`08`	`3`	`ENG`	`@0 Dark matter @5 33`
C03	`09`	`3`	`FRE`	`@0 Amas globulaire @5 34`
C03	`09`	`3`	`ENG`	`@0 Globular clusters @5 34`
C03	`10`	`X`	`FRE`	`@0 Rapport masse luminosité @5 35`
C03	`10`	`X`	`ENG`	`@0 Mass to light ratio @5 35`
C03	`10`	`X`	`SPA`	`@0 Relación masa luminosidad @5 35`
C03	`11`	`X`	`FRE`	`@0 Galaxies compagnons @5 36`
C03	`11`	`X`	`ENG`	`@0 Satellite galaxies @5 36`
C03	`11`	`X`	`SPA`	`@0 Galaxias satélite @5 36`
C03	`12`	`3`	`FRE`	`@0 Groupe local @5 37`
C03	`12`	`3`	`ENG`	`@0 Local group @5 37`
C03	`13`	`3`	`FRE`	`@0 Cinématique @5 38`
C03	`13`	`3`	`ENG`	`@0 Kinematics @5 38`
C03	`14`	`3`	`FRE`	`@0 Dynamique @5 39`
C03	`14`	`3`	`ENG`	`@0 Dynamics @5 39`
C03	`15`	`X`	`FRE`	`@0 Satellite Mars @5 40`
C03	`15`	`X`	`ENG`	`@0 Mars satellite @5 40`
C03	`15`	`X`	`SPA`	`@0 Satélite Marte @5 40`
C03	`16`	`3`	`FRE`	`@0 Amas stellaire @5 41`
C03	`16`	`3`	`ENG`	`@0 Star clusters @5 41`
C03	`17`	`3`	`FRE`	`@0 Interaction tidale @4 CD @5 96`
C03	`17`	`3`	`ENG`	`@0 Tidal interaction @4 CD @5 96`
C03	`17`	`3`	`SPA`	`@0 Interacción tidal @4 CD @5 96`
N21				`@1 267`
N44	`01`			`@1 OTO`
N82				`@1 OTO`

Format Inist (serveur)

NO :	PASCAL 07-0409359 INIST
ET :	A Keck/DEIMOS spectroscopic survey of faint Galactic satellites : searching for the least massive dwarf galaxies
AU :	MARTIN (N. F.); IBATA (R. A.); CHAPMAN (S. C.); IRWIN (M.); LEWIS (G. F.)
AF :	Max-Planck-Institut für Astronomie, Königstuhl 17/69117 Heidelberg/Allemagne (1 aut.); Observatoire de Strasbourg, 11, rue de l'Université/67000 Strasbourg/France (2 aut.); Institute of Astronomy, Madingley Road/Cambridge CB3 0HA/Royaume-Uni (3 aut., 4 aut.); Department of Physics and Astronomy, University of Victoria/Victoria, BC, V8P 1A1/Canada (3 aut.); Institute of Astronomy, School of Physics, A29 University of Sydney/NSW 2006/Australie (5 aut.)
DT :	Publication en série; Niveau analytique
SO :	Monthly Notices of the Royal Astronomical Society; ISSN 0035-8711; Coden MNRAA4; Royaume-Uni; Da. 2007; Vol. 380; No. 1; Pp. 281-300; Bibl. 1/2 p.
LA :	Anglais
EA :	We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Bootes, Ursa Major I, Ursa Major II and Willman 1 (Will). Using the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, we have obtained samples that contain from ∼ 15 to ∼85 probable members of these satellites for which we derive radial velocities precise to a few km s^-1 down to i ∼ 21-22. About half of these stars are observed with a high enough signal-to-noise ratio to estimate their metallicity to within ±0.2 dex. The characteristics of all the observed stars are made available, along with those of the Canes Venatici I dwarf galaxy that have been analysed in a companion paper. From this data set, we show that Ursa Major II is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (ù_r = 115 ± 5kms^-1) is in good agreement with simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark matter dominated systems (under the usual assumptions of symmetry and virial equilibrium). In particular, we show that despite its small size and faintness, the Will object is not a globular cluster given its metallicity scatter over -2.0 ≤ [Fe/H] ≤ -1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3 +2.3-1.3 km s^-1 around a systemic velocity of -12.3 ± 2.3 km s^-1 which implies a mass-to-light ratio of ∼700 and a total mass of ∼5 x 10⁵ M_O for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 10⁷ M_O limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modelling and an extended search for potential extratidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.
CC :	001E03
FD :	Deimos; Galaxies naines; Voie lactée; Vitesse radiale; Rapport signal bruit; Métallicité; Dispersion vitesse; Matière sombre; Amas globulaire; Rapport masse luminosité; Galaxies compagnons; Groupe local; Cinématique; Dynamique; Satellite Mars; Amas stellaire; Interaction tidale
ED :	Deimos; Dwarf galaxies; Milky Way; Radial velocity; Signal-to-noise ratio; Metallicity; Velocity dispersion; Dark matter; Globular clusters; Mass to light ratio; Satellite galaxies; Local group; Kinematics; Dynamics; Mars satellite; Star clusters; Tidal interaction
SD :	Metalicidad; Dispersión velocidad; Relación masa luminosidad; Galaxias satélite; Satélite Marte; Interacción tidal
LO :	INIST-2067.354000149667830230
ID :	07-0409359

Links to Exploration step

Pascal:07-0409359

Le document en format XML

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<front><div type="abstract" xml:lang="en">We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Bootes, Ursa Major I, Ursa Major II and Willman 1 (Will). Using the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, we have obtained samples that contain from ∼ 15 to ∼85 probable members of these satellites for which we derive radial velocities precise to a few km s<sup>-1</sup>
 down to i ∼ 21-22. About half of these stars are observed with a high enough signal-to-noise ratio to estimate their metallicity to within ±0.2 dex. The characteristics of all the observed stars are made available, along with those of the Canes Venatici I dwarf galaxy that have been analysed in a companion paper. From this data set, we show that Ursa Major II is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (ù<sub>r</sub>
 = 115 ± 5kms<sup>-1</sup>
) is in good agreement with simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark matter dominated systems (under the usual assumptions of symmetry and virial equilibrium). In particular, we show that despite its small size and faintness, the Will object is not a globular cluster given its metallicity scatter over -2.0 ≤ [Fe/H] ≤ -1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3 +2.3-1.3 km s<sup>-1</sup>
 around a systemic velocity of -12.3 ± 2.3 km s<sup>-1</sup>
 which implies a mass-to-light ratio of ∼700 and a total mass of ∼5 x 10<sup>5</sup>
 M<sub>O</sub>
 for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 10<sup>7</sup>
 M<sub>O</sub>
 limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modelling and an extended search for potential extratidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.</div>
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<fA14 i1="01"><s1>Max-Planck-Institut für Astronomie, Königstuhl 17</s1>
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<s3>CAN</s3>
<sZ>3 aut.</sZ>
</fA14>
<fA14 i1="05"><s1>Institute of Astronomy, School of Physics, A29 University of Sydney</s1>
<s2>NSW 2006</s2>
<s3>AUS</s3>
<sZ>5 aut.</sZ>
</fA14>
<fA20><s1>281-300</s1>
</fA20>
<fA21><s1>2007</s1>
</fA21>
<fA23 i1="01"><s0>ENG</s0>
</fA23>
<fA43 i1="01"><s1>INIST</s1>
<s2>2067</s2>
<s5>354000149667830230</s5>
</fA43>
<fA44><s0>0000</s0>
<s1>© 2007 INIST-CNRS. All rights reserved.</s1>
</fA44>
<fA45><s0>1/2 p.</s0>
</fA45>
<fA47 i1="01" i2="1"><s0>07-0409359</s0>
</fA47>
<fA60><s1>P</s1>
</fA60>
<fA61><s0>A</s0>
</fA61>
<fA64 i1="01" i2="1"><s0>Monthly Notices of the Royal Astronomical Society</s0>
</fA64>
<fA66 i1="01"><s0>GBR</s0>
</fA66>
<fC01 i1="01" l="ENG"><s0>We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Bootes, Ursa Major I, Ursa Major II and Willman 1 (Will). Using the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, we have obtained samples that contain from ∼ 15 to ∼85 probable members of these satellites for which we derive radial velocities precise to a few km s<sup>-1</sup>
 down to i ∼ 21-22. About half of these stars are observed with a high enough signal-to-noise ratio to estimate their metallicity to within ±0.2 dex. The characteristics of all the observed stars are made available, along with those of the Canes Venatici I dwarf galaxy that have been analysed in a companion paper. From this data set, we show that Ursa Major II is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (ù<sub>r</sub>
 = 115 ± 5kms<sup>-1</sup>
) is in good agreement with simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark matter dominated systems (under the usual assumptions of symmetry and virial equilibrium). In particular, we show that despite its small size and faintness, the Will object is not a globular cluster given its metallicity scatter over -2.0 ≤ [Fe/H] ≤ -1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3 +2.3-1.3 km s<sup>-1</sup>
 around a systemic velocity of -12.3 ± 2.3 km s<sup>-1</sup>
 which implies a mass-to-light ratio of ∼700 and a total mass of ∼5 x 10<sup>5</sup>
 M<sub>O</sub>
 for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 10<sup>7</sup>
 M<sub>O</sub>
 limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modelling and an extended search for potential extratidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.</s0>
</fC01>
<fC02 i1="01" i2="3"><s0>001E03</s0>
</fC02>
<fC03 i1="01" i2="3" l="FRE"><s0>Deimos</s0>
<s5>26</s5>
</fC03>
<fC03 i1="01" i2="3" l="ENG"><s0>Deimos</s0>
<s5>26</s5>
</fC03>
<fC03 i1="02" i2="3" l="FRE"><s0>Galaxies naines</s0>
<s5>27</s5>
</fC03>
<fC03 i1="02" i2="3" l="ENG"><s0>Dwarf galaxies</s0>
<s5>27</s5>
</fC03>
<fC03 i1="03" i2="3" l="FRE"><s0>Voie lactée</s0>
<s5>28</s5>
</fC03>
<fC03 i1="03" i2="3" l="ENG"><s0>Milky Way</s0>
<s5>28</s5>
</fC03>
<fC03 i1="04" i2="3" l="FRE"><s0>Vitesse radiale</s0>
<s5>29</s5>
</fC03>
<fC03 i1="04" i2="3" l="ENG"><s0>Radial velocity</s0>
<s5>29</s5>
</fC03>
<fC03 i1="05" i2="3" l="FRE"><s0>Rapport signal bruit</s0>
<s5>30</s5>
</fC03>
<fC03 i1="05" i2="3" l="ENG"><s0>Signal-to-noise ratio</s0>
<s5>30</s5>
</fC03>
<fC03 i1="06" i2="X" l="FRE"><s0>Métallicité</s0>
<s5>31</s5>
</fC03>
<fC03 i1="06" i2="X" l="ENG"><s0>Metallicity</s0>
<s5>31</s5>
</fC03>
<fC03 i1="06" i2="X" l="SPA"><s0>Metalicidad</s0>
<s5>31</s5>
</fC03>
<fC03 i1="07" i2="X" l="FRE"><s0>Dispersion vitesse</s0>
<s5>32</s5>
</fC03>
<fC03 i1="07" i2="X" l="ENG"><s0>Velocity dispersion</s0>
<s5>32</s5>
</fC03>
<fC03 i1="07" i2="X" l="SPA"><s0>Dispersión velocidad</s0>
<s5>32</s5>
</fC03>
<fC03 i1="08" i2="3" l="FRE"><s0>Matière sombre</s0>
<s5>33</s5>
</fC03>
<fC03 i1="08" i2="3" l="ENG"><s0>Dark matter</s0>
<s5>33</s5>
</fC03>
<fC03 i1="09" i2="3" l="FRE"><s0>Amas globulaire</s0>
<s5>34</s5>
</fC03>
<fC03 i1="09" i2="3" l="ENG"><s0>Globular clusters</s0>
<s5>34</s5>
</fC03>
<fC03 i1="10" i2="X" l="FRE"><s0>Rapport masse luminosité</s0>
<s5>35</s5>
</fC03>
<fC03 i1="10" i2="X" l="ENG"><s0>Mass to light ratio</s0>
<s5>35</s5>
</fC03>
<fC03 i1="10" i2="X" l="SPA"><s0>Relación masa luminosidad</s0>
<s5>35</s5>
</fC03>
<fC03 i1="11" i2="X" l="FRE"><s0>Galaxies compagnons</s0>
<s5>36</s5>
</fC03>
<fC03 i1="11" i2="X" l="ENG"><s0>Satellite galaxies</s0>
<s5>36</s5>
</fC03>
<fC03 i1="11" i2="X" l="SPA"><s0>Galaxias satélite</s0>
<s5>36</s5>
</fC03>
<fC03 i1="12" i2="3" l="FRE"><s0>Groupe local</s0>
<s5>37</s5>
</fC03>
<fC03 i1="12" i2="3" l="ENG"><s0>Local group</s0>
<s5>37</s5>
</fC03>
<fC03 i1="13" i2="3" l="FRE"><s0>Cinématique</s0>
<s5>38</s5>
</fC03>
<fC03 i1="13" i2="3" l="ENG"><s0>Kinematics</s0>
<s5>38</s5>
</fC03>
<fC03 i1="14" i2="3" l="FRE"><s0>Dynamique</s0>
<s5>39</s5>
</fC03>
<fC03 i1="14" i2="3" l="ENG"><s0>Dynamics</s0>
<s5>39</s5>
</fC03>
<fC03 i1="15" i2="X" l="FRE"><s0>Satellite Mars</s0>
<s5>40</s5>
</fC03>
<fC03 i1="15" i2="X" l="ENG"><s0>Mars satellite</s0>
<s5>40</s5>
</fC03>
<fC03 i1="15" i2="X" l="SPA"><s0>Satélite Marte</s0>
<s5>40</s5>
</fC03>
<fC03 i1="16" i2="3" l="FRE"><s0>Amas stellaire</s0>
<s5>41</s5>
</fC03>
<fC03 i1="16" i2="3" l="ENG"><s0>Star clusters</s0>
<s5>41</s5>
</fC03>
<fC03 i1="17" i2="3" l="FRE"><s0>Interaction tidale</s0>
<s4>CD</s4>
<s5>96</s5>
</fC03>
<fC03 i1="17" i2="3" l="ENG"><s0>Tidal interaction</s0>
<s4>CD</s4>
<s5>96</s5>
</fC03>
<fC03 i1="17" i2="3" l="SPA"><s0>Interacción tidal</s0>
<s4>CD</s4>
<s5>96</s5>
</fC03>
<fN21><s1>267</s1>
</fN21>
<fN44 i1="01"><s1>OTO</s1>
</fN44>
<fN82><s1>OTO</s1>
</fN82>
</pA>
</standard>
<server><NO>PASCAL 07-0409359 INIST</NO>
<ET>A Keck/DEIMOS spectroscopic survey of faint Galactic satellites : searching for the least massive dwarf galaxies</ET>
<AU>MARTIN (N. F.); IBATA (R. A.); CHAPMAN (S. C.); IRWIN (M.); LEWIS (G. F.)</AU>
<AF>Max-Planck-Institut für Astronomie, Königstuhl 17/69117 Heidelberg/Allemagne (1 aut.); Observatoire de Strasbourg, 11, rue de l'Université/67000 Strasbourg/France (2 aut.); Institute of Astronomy, Madingley Road/Cambridge CB3 0HA/Royaume-Uni (3 aut., 4 aut.); Department of Physics and Astronomy, University of Victoria/Victoria, BC, V8P 1A1/Canada (3 aut.); Institute of Astronomy, School of Physics, A29 University of Sydney/NSW 2006/Australie (5 aut.)</AF>
<DT>Publication en série; Niveau analytique</DT>
<SO>Monthly Notices of the Royal Astronomical Society; ISSN 0035-8711; Coden MNRAA4; Royaume-Uni; Da. 2007; Vol. 380; No. 1; Pp. 281-300; Bibl. 1/2 p.</SO>
<LA>Anglais</LA>
<EA>We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Bootes, Ursa Major I, Ursa Major II and Willman 1 (Will). Using the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, we have obtained samples that contain from ∼ 15 to ∼85 probable members of these satellites for which we derive radial velocities precise to a few km s<sup>-1</sup>
 down to i ∼ 21-22. About half of these stars are observed with a high enough signal-to-noise ratio to estimate their metallicity to within ±0.2 dex. The characteristics of all the observed stars are made available, along with those of the Canes Venatici I dwarf galaxy that have been analysed in a companion paper. From this data set, we show that Ursa Major II is the only object that does not show a clear radial velocity peak. However, the measured systemic radial velocity (ù<sub>r</sub>
 = 115 ± 5kms<sup>-1</sup>
) is in good agreement with simulations in which this object is the progenitor of the recently discovered Orphan Stream. The three other satellites show velocity dispersions that make them highly dark matter dominated systems (under the usual assumptions of symmetry and virial equilibrium). In particular, we show that despite its small size and faintness, the Will object is not a globular cluster given its metallicity scatter over -2.0 ≤ [Fe/H] ≤ -1.0 and is therefore almost certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity dispersion of only 4.3 +2.3-1.3 km s<sup>-1</sup>
 around a systemic velocity of -12.3 ± 2.3 km s<sup>-1</sup>
 which implies a mass-to-light ratio of ∼700 and a total mass of ∼5 x 10<sup>5</sup>
 M<sub>O</sub>
 for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 10<sup>7</sup>
 M<sub>O</sub>
 limit that had until now never been crossed for Milky Way and Andromeda satellite galaxies may only be an observational limit and that fainter, less massive systems exist within the Local Group. However, more modelling and an extended search for potential extratidal stars are required to rule out the possibility that these systems have not been significantly heated by tidal interaction.</EA>
<CC>001E03</CC>
<FD>Deimos; Galaxies naines; Voie lactée; Vitesse radiale; Rapport signal bruit; Métallicité; Dispersion vitesse; Matière sombre; Amas globulaire; Rapport masse luminosité; Galaxies compagnons; Groupe local; Cinématique; Dynamique; Satellite Mars; Amas stellaire; Interaction tidale</FD>
<ED>Deimos; Dwarf galaxies; Milky Way; Radial velocity; Signal-to-noise ratio; Metallicity; Velocity dispersion; Dark matter; Globular clusters; Mass to light ratio; Satellite galaxies; Local group; Kinematics; Dynamics; Mars satellite; Star clusters; Tidal interaction</ED>
<SD>Metalicidad; Dispersión velocidad; Relación masa luminosidad; Galaxias satélite; Satélite Marte; Interacción tidal</SD>
<LO>INIST-2067.354000149667830230</LO>
<ID>07-0409359</ID>
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A Keck/DEIMOS spectroscopic survey of faint Galactic satellites : searching for the least massive dwarf galaxies

A Keck/DEIMOS spectroscopic survey of faint Galactic satellites : searching for the least massive dwarf galaxies

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