A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
Identifieur interne : 002401 ( Istex/Curation ); précédent : 002400; suivant : 002402A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
Auteurs : N. F. Martin [Allemagne] ; R. A. Ibata [France] ; S. C. Chapman [Canada] ; M. Irwin ; G. F. Lewis [Australie]Source :
- Monthly Notices of the Royal Astronomical Society [ 0035-8711 ] ; 2007-09-01.
Abstract
We present the results of a spectroscopic survey of the recently discovered faint Milky Way satellites Boötes, Ursa Major I, Ursa Major II and Willman 1 (Wil1). 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 (vr= 115 ± 5 km s−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 Wil1 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 × 105 M⊙ for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 107 M⊙ 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.
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DOI: 10.1111/j.1365-2966.2007.12055.x
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N. F. Martin<affiliation><mods:affiliation></mods:affiliation><wicri:noCountry code="syntax">???</wicri:noCountry></affiliation><affiliation wicri:level="1"><mods:affiliation>E-mail: martin@mpia-hd.mpg.de</mods:affiliation><country wicri:rule="url">Allemagne</country></affiliation><affiliation><mods:affiliation>Institute of Astronomy, Madingley Road, Cambridge CB3 0HA</mods:affiliation><wicri:noCountry code="subField">0HA</wicri:noCountry></affiliation>Le document en format XML
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Ibata</name><affiliation wicri:level="1"><mods:affiliation>Observatoire de Strasbourg, 11, rue de l'Université, F-67000 Strasbourg, France</mods:affiliation><country xml:lang="fr">France</country><wicri:regionArea>Observatoire de Strasbourg, 11, rue de l'Université, F-67000 Strasbourg</wicri:regionArea></affiliation></author><author><name sortKey="Chapman, S C" sort="Chapman, S C" uniqKey="Chapman S" first="S. C." last="Chapman">S. C. 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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 (vr= 115 ± 5 km s−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 Wil1 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 × 105 M⊙ for this satellite, making it the least massive satellite galaxy known to date. Such a low mass could mean that the 107 M⊙ 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></front></TEI></record>Pour manipuler ce document sous Unix (Dilib)
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