She Sees Shells by the Stellar Shore: A Kinematic View of NGC 253's Stellar Halo
Abstract
The stellar halos of nearby galaxies are fossil records of ancient mergers, providing insight into the formation and growth of these systems. These halos often contain substructure in the form of streams, shells, and debris fields that make up dynamically young remnants of past accretions. These remnants can be probed with resolved-star spectroscopic observations, giving insight into the kinematics of bygone satellite companions. Such observations have been made for the Milky Way (MW) and Andromeda, but are much more challenging and expensive to do outside the Local Group. The Local Volume has an abundance of MW-mass galaxies with richly structured halos, such as NGC 253. Leveraging the power of Magellan's M2FS fiber-fed multiobject spectrograph, we have obtained medium-resolution spectra of 225 stars centered on NGC 253's southwestern shell. These spectra enabled us to make the first-ever measurement of the resolved-star stellar kinematics for 89 stars in NGC 253's halo. We also detect substructure in several ways and identify regions likely to be accreted and in-situ, finding among them a low-velocity region coincident with the previously reported SW shell we believe was accreted recently, and an in-situ component that traces the outer disk. After subtracting NGC 253's systemic velocity, we measure median line-of-sight velocities of −34−12+16 km/s and 167−14+16 km/s for the accreted and in-situ populations, respectively. This work highlights the utility of kinematics to differentiate between accreted and in-situ stars, and acts as a pathfinder for future observations with next-generation 30 m telescopes and wide-field multiobject spectrographs.
Versions
Related
- A Detailed GASKAP-HI View of Shells and Loops in the Magellanic Bridge
- A detailed GASKAP-H i view of shells and loops in the Magellanic Bridge
- A morpho-kinematic view of the Necklace nebula
- A morpho-kinematic view of the Necklace nebula
- The Impact of Non-Gaussian Line Spread Functions on Stellar Kinematic Recovery: Consequences for Dynamical Models
BibTeX
@misc{gozman2026sees,
title = {{She Sees Shells by the Stellar Shore: A Kinematic View of NGC 253's Stellar Halo}},
author = {Katya Gozman and Eric F. Bell and Richard D'Souza and Mario Mateo and John I. Bailey III and Antonela Monachesi and Camila Beltrand},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.05493},
eprint = {2611.05493},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.05493},
}
RIS
TY - UNPB
TI - She Sees Shells by the Stellar Shore: A Kinematic View of NGC 253's Stellar Halo
AU - Katya Gozman
AU - Eric F. Bell
AU - Richard D'Souza
AU - Mario Mateo
AU - John I. Bailey III
AU - Antonela Monachesi
AU - Camila Beltrand
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.05493
UR - https://arxiv.org/abs/2611.05493
AB - The stellar halos of nearby galaxies are fossil records of ancient mergers, providing insight into the formation and growth of these systems. These halos often contain substructure in the form of streams, shells, and debris fields that make up dynamically young remnants of past accretions. These remnants can be probed with resolved-star spectroscopic observations, giving insight into the kinematics of bygone satellite companions. Such observations have been made for the Milky Way (MW) and Andromeda, but are much more challenging and expensive to do outside the Local Group. The Local Volume has an abundance of MW-mass galaxies with richly structured halos, such as NGC 253. Leveraging the power of Magellan's M2FS fiber-fed multiobject spectrograph, we have obtained medium-resolution spectra of 225 stars centered on NGC 253's southwestern shell. These spectra enabled us to make the first-ever measurement of the resolved-star stellar kinematics for 89 stars in NGC 253's halo. We also detect substructure in several ways and identify regions likely to be accreted and in-situ, finding among them a low-velocity region coincident with the previously reported SW shell we believe was accreted recently, and an in-situ component that traces the outer disk. After subtracting NGC 253's systemic velocity, we measure median line-of-sight velocities of −34_−12^+16 km/s and 167_−14^+16 km/s for the accreted and in-situ populations, respectively. This work highlights the utility of kinematics to differentiate between accreted and in-situ stars, and acts as a pathfinder for future observations with next-generation 30 m telescopes and wide-field multiobject spectrographs.
ER -