We point out an anticorrelation between the central dark matter (DM) densities of the bright Milky Way dwarf spheroidal galaxies (dSphs) and their orbital pericenter distances inferred from Gaia data. The dSphs that have not come close to the Milky Way centre (like Fornax, Carina and Sextans) are less dense in DM than those that have come closer (like Draco and Ursa Minor). The same anticorrelation cannot be inferred for the ultrafaint dSphs due to large scatter, while a trend that dSphs with more extended stellar distributions tend to have lower DM densities emerges with ultrafaints. We discuss how these inferences constrain proposed solutions to the Milky Way’s too-big-to-fail problem and provide new clues to decipher the nature of DM.
Stellar proper motions in the outskirts of classical dwarf spheroidal galaxies with Gaia EDR3
We use Gaia EDR3 data to identify stars associated with six classical dwarf spheroidals (dSphs) (Draco, Ursa Minor, Sextans, Sculptor, Fornax, Carina) at their outermost radii, beyond their nominal King stellar limiting radius. For all of the dSphs examined, we find radial velocity matches with stars residing beyond the King limiting radius and with ${\gt}50{{\ \rm per\ cent}}$ astrometric probability (four in Draco, two in Ursa Minor, eight in Sextans, two in Sculptor, 12 in Fornax, and five in Carina), indicating that these stars are associated with their respective dSphs at high probability. We compare the positions of our candidate ‘extra-tidal’ stars with the orbital tracks of the galaxies, and identify stars, both with and without radial velocity matches, that are consistent with lying along the orbital track of the satellites. However, given the small number of candidate stars, we cannot make any conclusive statements about the significance of these spatially correlated stars. Cross matching with publicly available catalogues of RR Lyrae, we find one RR Lyrae candidate with ${\gt}50{{\ \rm per\ cent}}$ astrometric probability outside the limiting radius in each of Sculptor and Fornax, two such candidates in Draco, nine in Ursa Minor, seven in Sextans, and zero in Carina. Follow-up spectra on all of our candidates, including possible metallicity information, will help confirm association with their respective dSphs, and could represent evidence for extended stellar haloes or tidal debris around these classical dSphs.
more » « less- Award ID(s):
- 1813881
- NSF-PAR ID:
- 10366462
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 512
- Issue:
- 4
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 5601-5619
- Size(s):
- ["p. 5601-5619"]
- Sponsoring Org:
- National Science Foundation
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