Characterizing stellar halo populations – I. An extended distribution function for halo K giants
We fit an extended distribution function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration survey. These stars are detected to radii ∼80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metalli...
| Main Authors: | , |
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| Format: | Journal article |
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Oxford University Press
2016
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| _version_ | 1826269469556604928 |
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| author | Das, P Binney, J |
| author_facet | Das, P Binney, J |
| author_sort | Das, P |
| collection | OXFORD |
| description | We fit an extended distribution function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration survey. These stars are detected to radii ∼80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ∼−2 to ∼−4 at large radii. The halo's axis ratio increases with radius from 0.7 to almost unity. The metal-rich stars are more tightly confined in action space than the metal-poor stars and form a more flattened structure. A weak metallicity gradient ∼−0.001 dex kpc−1, a small gradient in the dispersion in [Fe/H] of ∼0.001 dex kpc−1, and a higher degree of radial anisotropy in metal-richer stars result. Lognormal components with peaks at ∼−1.5 and ∼−2.3 are required to capture the overall metallicity distribution, suggestive of the existence of two populations of K giants. The spherical anisotropy parameter varies between 0.3 in the inner halo to isotropic in the outer halo. If the Sagittarius stream is included, a very similar model is found but with a stronger degree of radial anisotropy throughout. |
| first_indexed | 2024-03-06T21:25:32Z |
| format | Journal article |
| id | oxford-uuid:42f8781a-193b-49ff-a284-e4c8681a86fb |
| institution | University of Oxford |
| last_indexed | 2024-03-06T21:25:32Z |
| publishDate | 2016 |
| publisher | Oxford University Press |
| record_format | dspace |
| spelling | oxford-uuid:42f8781a-193b-49ff-a284-e4c8681a86fb2022-03-26T14:52:30ZCharacterizing stellar halo populations – I. An extended distribution function for halo K giantsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:42f8781a-193b-49ff-a284-e4c8681a86fbSymplectic Elements at OxfordOxford University Press2016Das, PBinney, JWe fit an extended distribution function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration survey. These stars are detected to radii ∼80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ∼−2 to ∼−4 at large radii. The halo's axis ratio increases with radius from 0.7 to almost unity. The metal-rich stars are more tightly confined in action space than the metal-poor stars and form a more flattened structure. A weak metallicity gradient ∼−0.001 dex kpc−1, a small gradient in the dispersion in [Fe/H] of ∼0.001 dex kpc−1, and a higher degree of radial anisotropy in metal-richer stars result. Lognormal components with peaks at ∼−1.5 and ∼−2.3 are required to capture the overall metallicity distribution, suggestive of the existence of two populations of K giants. The spherical anisotropy parameter varies between 0.3 in the inner halo to isotropic in the outer halo. If the Sagittarius stream is included, a very similar model is found but with a stronger degree of radial anisotropy throughout. |
| spellingShingle | Das, P Binney, J Characterizing stellar halo populations – I. An extended distribution function for halo K giants |
| title | Characterizing stellar halo populations – I. An extended distribution function for halo K giants |
| title_full | Characterizing stellar halo populations – I. An extended distribution function for halo K giants |
| title_fullStr | Characterizing stellar halo populations – I. An extended distribution function for halo K giants |
| title_full_unstemmed | Characterizing stellar halo populations – I. An extended distribution function for halo K giants |
| title_short | Characterizing stellar halo populations – I. An extended distribution function for halo K giants |
| title_sort | characterizing stellar halo populations i an extended distribution function for halo k giants |
| work_keys_str_mv | AT dasp characterizingstellarhalopopulationsianextendeddistributionfunctionforhalokgiants AT binneyj characterizingstellarhalopopulationsianextendeddistributionfunctionforhalokgiants |