The Study of Detailed Morphology of Milky Way Dwarf Galaxies: Draco and Boötes I
Abstract
We present a photometric study of the outer stellar structures of the Milky Way dwarf spheroidal galaxies (dSphs) Draco and Boötes I, using deep wide-field imaging data. The old main-sequence stars are used to trace their spatial distributions beyond their tidal radii. We derive global structural parameters and radial profiles of number density, ellipticity, and position angle from their stellar distributions. Draco and Boötes I show contrasting features. Draco shows no prominent extended stellar distribution, although weak elongations are detected toward the eastern and northwestern directions. Its stellar distribution remains relatively compact compared with its estimated Jacobi tidal radius (rJ=57.2+13.5−11.1 arcmin), suggesting that the stellar component is tightly bound by its gravitational potential. In contrast, the radial number-density profiles of Boötes I along several directions show excess from the best-fit exponential profile outside of around r∼20 arcmin, near the estimated Jacobi radius (rJ=21.6+9.3−7.6 arcmin). In addition, the ellipticity of Draco decreases with radius, whereas that of Boötes I increases toward larger radii. Bo"otes I also exhibits a prominent S-shaped stellar structure extending approximately along its orbital direction. Together, the radial density excess, increasing ellipticity, and S-shaped morphology suggest that the outer stellar structure of Boötes I may trace tidal tails produced by interactions with the Milky Way. The contrasting morphologies of Draco and Boötes I further suggest that the response of dwarf galaxies to the Milky Way tidal field may depend not only on their orbital histories, but also on the internal structure of their dark-matter halos.
Related
- Spectroscopic Confirmation of the Milky Way Satellites Boötes V and Leo Minor I and the LMC Satellite DELVE 2: Three Small Ultra-Faint Dwarf Galaxies
- A detailed star formation history of the distant Milky Way satellite Canes Venatici I: An old dwarf spheroidal forming most of its stars after reionisation
- Star formation history of Draco revealed by DESI DR1: suppressed early star formation efficiency for Milky Way dwarf galaxies
- Reconstructing the orbits of Milky Way dwarf galaxies: A Large Magellanic Cloud perspective
- Prospects for Near-Far Constraints on Reionization from Simulated LSST Observations of Milky Way Dwarf Galaxies and Stellar Streams
BibTeX
@misc{sato2026study,
title = {{The Study of Detailed Morphology of Milky Way Dwarf Galaxies: Draco and Boötes I}},
author = {Kyosuke S. Sato and Masafumi Yagi and Sakurako Okamoto},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2609.16476},
eprint = {2609.16476},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.16476},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Study of Detailed Morphology of Milky Way Dwarf Galaxies: Draco and Boötes I
AU - Kyosuke S. Sato
AU - Masafumi Yagi
AU - Sakurako Okamoto
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2609.16476
UR - https://arxiv.org/abs/2609.16476
AB - We present a photometric study of the outer stellar structures of the Milky Way dwarf spheroidal galaxies (dSphs) Draco and Boötes I, using deep wide-field imaging data. The old main-sequence stars are used to trace their spatial distributions beyond their tidal radii. We derive global structural parameters and radial profiles of number density, ellipticity, and position angle from their stellar distributions. Draco and Boötes I show contrasting features. Draco shows no prominent extended stellar distribution, although weak elongations are detected toward the eastern and northwestern directions. Its stellar distribution remains relatively compact compared with its estimated Jacobi tidal radius (r_J=57.2^+13.5_−11.1 arcmin), suggesting that the stellar component is tightly bound by its gravitational potential. In contrast, the radial number-density profiles of Boötes I along several directions show excess from the best-fit exponential profile outside of around r∼20 arcmin, near the estimated Jacobi radius (r_J=21.6^+9.3_−7.6 arcmin). In addition, the ellipticity of Draco decreases with radius, whereas that of Boötes I increases toward larger radii. Bo"otes I also exhibits a prominent S-shaped stellar structure extending approximately along its orbital direction. Together, the radial density excess, increasing ellipticity, and S-shaped morphology suggest that the outer stellar structure of Boötes I may trace tidal tails produced by interactions with the Milky Way. The contrasting morphologies of Draco and Boötes I further suggest that the response of dwarf galaxies to the Milky Way tidal field may depend not only on their orbital histories, but also on the internal structure of their dark-matter halos.
ER -