Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes II
In this paper, we present a chemical and kinematic analysis of two ultrafaint dwarf galaxies (UFDs), Aquarius II (Aqu II) and Boötes II (Boo II), using Magellan/IMACS spectroscopy. We present the largest sample of member stars for Boo II (12), and the largest sample of red giant branch members with...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/acc943 |
| _version_ | 1827826810806599680 |
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| author | Jordan Bruce Ting S. Li Andrew B. Pace Mairead Heiger Ying-Yi Song Joshua D. Simon |
| author_facet | Jordan Bruce Ting S. Li Andrew B. Pace Mairead Heiger Ying-Yi Song Joshua D. Simon |
| author_sort | Jordan Bruce |
| collection | DOAJ |
| description | In this paper, we present a chemical and kinematic analysis of two ultrafaint dwarf galaxies (UFDs), Aquarius II (Aqu II) and Boötes II (Boo II), using Magellan/IMACS spectroscopy. We present the largest sample of member stars for Boo II (12), and the largest sample of red giant branch members with metallicity measurements for Aqu II (eight). In both UFDs, over 80% of targets selected based on Gaia proper motions turned out to be spectroscopic members. In order to maximize the accuracy of stellar kinematic measurements, we remove the identified binary stars and RR Lyrae variables. For Aqu II, we measure a systemic velocity of −65.3 ± 1.8 km s ^−1 and a metallicity of [Fe/H] = $-{2.57}_{-0.17}^{+0.17}$ . When compared with previous measurements, these values display a ∼6 km s ^−1 difference in radial velocity and a decrease of 0.27 dex in metallicity. Similarly for Boo II, we measure a systemic velocity of $-{130.4}_{-1.1}^{+1.4}$ km s ^−1 , more than 10 km s ^−1 different from the literature, a metallicity almost 1 dex smaller at [Fe/H] = $-{2.71}_{-0.10}^{+0.11}$ , and a velocity dispersion 3 times smaller at ${\sigma }_{{v}_{\mathrm{hel}}}={2.9}_{-1.2}^{+1.6}$ km s ^−1 . Additionally, we derive systemic proper-motion parameters and model the orbits of both UFDs. Finally, we highlight the extremely dark-matter-dominated nature of Aqu II and compute the J-factor for both galaxies to aid searches of dark matter annihilation. Despite the small size and close proximity of Boo II, it is an intermediate target for the indirect detection of dark matter annihilation due to its low-velocity dispersion and corresponding low dark matter density. |
| first_indexed | 2024-03-12T03:17:51Z |
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| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T03:17:51Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-16df80dd259c4b649ad28f1a0156d6d72023-09-03T14:08:14ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-01950216710.3847/1538-4357/acc943Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes IIJordan Bruce0Ting S. Li1https://orcid.org/0000-0002-9110-6163Andrew B. Pace2https://orcid.org/0000-0002-6021-8760Mairead Heiger3https://orcid.org/0000-0002-2446-8332Ying-Yi Song4https://orcid.org/0000-0002-6270-8851Joshua D. Simon5https://orcid.org/0000-0002-4733-4994David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4 CanadaDavid A. Dunlap Department of Astronomy & Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4 Canada; Dunlap Institute for Astronomy & Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, CanadaMcWillliams Center for Cosmology, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, PA 15213, USADavid A. Dunlap Department of Astronomy & Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4 Canada; Dunlap Institute for Astronomy & Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, CanadaDavid A. Dunlap Department of Astronomy & Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4 Canada; Dunlap Institute for Astronomy & Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, CanadaObservatories of the Carnegie Institution for Science , 813 Santa Barbara Street, Pasadena, CA 91101, USAIn this paper, we present a chemical and kinematic analysis of two ultrafaint dwarf galaxies (UFDs), Aquarius II (Aqu II) and Boötes II (Boo II), using Magellan/IMACS spectroscopy. We present the largest sample of member stars for Boo II (12), and the largest sample of red giant branch members with metallicity measurements for Aqu II (eight). In both UFDs, over 80% of targets selected based on Gaia proper motions turned out to be spectroscopic members. In order to maximize the accuracy of stellar kinematic measurements, we remove the identified binary stars and RR Lyrae variables. For Aqu II, we measure a systemic velocity of −65.3 ± 1.8 km s ^−1 and a metallicity of [Fe/H] = $-{2.57}_{-0.17}^{+0.17}$ . When compared with previous measurements, these values display a ∼6 km s ^−1 difference in radial velocity and a decrease of 0.27 dex in metallicity. Similarly for Boo II, we measure a systemic velocity of $-{130.4}_{-1.1}^{+1.4}$ km s ^−1 , more than 10 km s ^−1 different from the literature, a metallicity almost 1 dex smaller at [Fe/H] = $-{2.71}_{-0.10}^{+0.11}$ , and a velocity dispersion 3 times smaller at ${\sigma }_{{v}_{\mathrm{hel}}}={2.9}_{-1.2}^{+1.6}$ km s ^−1 . Additionally, we derive systemic proper-motion parameters and model the orbits of both UFDs. Finally, we highlight the extremely dark-matter-dominated nature of Aqu II and compute the J-factor for both galaxies to aid searches of dark matter annihilation. Despite the small size and close proximity of Boo II, it is an intermediate target for the indirect detection of dark matter annihilation due to its low-velocity dispersion and corresponding low dark matter density.https://doi.org/10.3847/1538-4357/acc943Dwarf galaxiesDark matterStellar kinematicsMilky Way GalaxySpectroscopyBinary stars |
| spellingShingle | Jordan Bruce Ting S. Li Andrew B. Pace Mairead Heiger Ying-Yi Song Joshua D. Simon Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes II The Astrophysical Journal Dwarf galaxies Dark matter Stellar kinematics Milky Way Galaxy Spectroscopy Binary stars |
| title | Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes II |
| title_full | Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes II |
| title_fullStr | Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes II |
| title_full_unstemmed | Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes II |
| title_short | Spectroscopic Analysis of Milky Way Outer Halo Satellites: Aquarius II and Boötes II |
| title_sort | spectroscopic analysis of milky way outer halo satellites aquarius ii and bootes ii |
| topic | Dwarf galaxies Dark matter Stellar kinematics Milky Way Galaxy Spectroscopy Binary stars |
| url | https://doi.org/10.3847/1538-4357/acc943 |
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