Hoag-type Galaxies: A Photometric Study of the Cores and Rings of Thirty Systems from the DESI Legacy Survey
Abstract
Hoag-type galaxies contain a smooth central core surrounded by a detached outer ring, but their rarity has limited previous studies mainly to individual systems. We identify thirty galaxies with apparent Hoag-type morphology in DESI imaging by visually inspecting two machine-learning ring-galaxy catalogues and analyse their core and ring properties using DESI Legacy Imaging Surveys g, r, and z images. We measure the rings after subtracting two-dimensional core models and compare the cores with matched SDSS galaxies. The cores lie predominantly on the red sequence, whereas the rings span a broader colour range extending toward the blue cloud. The cores broadly follow early-type mass scaling relations, but their mass-matched distributions tend towards slightly bluer colours, smaller sizes, higher stellar-mass surface densities, and lower concentrations and Sérsic indices. Of the 16 systems with SDSS group information, 14 (87.5 per cent) are centrals, compared with ∼64% in the mass-matched early-type control sample. The halo-mass and large-scale overdensity distributions become much more similar after central--satellite status is also matched. Ring stellar-mass surface density and normalized width decrease with increasing core-plus-inner-halo to ring mass ratio. Most core R90 values lie inside the outermost stable circular orbit of a simplified core-plus-ring model, while the rings frequently extend across its unstable interval. The slightly bluer core colours, lower concentrations, and lower Sérsic indices suggest a possible secular contribution, but the compact, dense cores imply more complex structural assembly than a simple diffuse-pseudobulge origin. The high central fraction may favour gas retention and ring survival by reducing satellite-specific environmental processing. The diversity of ring properties nevertheless leaves room for multiple formation pathways.
Related
- The NIKA2 Cosmological Legacy Survey in COSMOS: Final 1.2,mm and 2,mm source catalogs and redshift distribution of dusty star-forming galaxies
- A probabilistic approach to separate mergers and jellyfish galaxies: Application of morphological non-parametric indexes to the DESI Legacy Survey
- J-PAS and FLAMINGO: Cosmic voids and void galaxies in the gravitational landscape of photometric surveys
- The occurrence rate of planets around subgiant stars from the TESS photometric survey
- An automated photometric pipeline for measuring the corotation radius of spiral galaxies
BibTeX
@misc{yang2026hoagtype,
title = {{Hoag-type Galaxies: A Photometric Study of the Cores and Rings of Thirty Systems from the DESI Legacy Survey}},
author = {Jingshuo Yang and Cheng Li},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.39629},
eprint = {2610.39629},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.39629},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Hoag-type Galaxies: A Photometric Study of the Cores and Rings of Thirty Systems from the DESI Legacy Survey
AU - Jingshuo Yang
AU - Cheng Li
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.39629
UR - https://arxiv.org/abs/2610.39629
AB - Hoag-type galaxies contain a smooth central core surrounded by a detached outer ring, but their rarity has limited previous studies mainly to individual systems. We identify thirty galaxies with apparent Hoag-type morphology in DESI imaging by visually inspecting two machine-learning ring-galaxy catalogues and analyse their core and ring properties using DESI Legacy Imaging Surveys g, r, and z images. We measure the rings after subtracting two-dimensional core models and compare the cores with matched SDSS galaxies. The cores lie predominantly on the red sequence, whereas the rings span a broader colour range extending toward the blue cloud. The cores broadly follow early-type mass scaling relations, but their mass-matched distributions tend towards slightly bluer colours, smaller sizes, higher stellar-mass surface densities, and lower concentrations and Sérsic indices. Of the 16 systems with SDSS group information, 14 (87.5 per cent) are centrals, compared with ∼64% in the mass-matched early-type control sample. The halo-mass and large-scale overdensity distributions become much more similar after central--satellite status is also matched. Ring stellar-mass surface density and normalized width decrease with increasing core-plus-inner-halo to ring mass ratio. Most core R_90 values lie inside the outermost stable circular orbit of a simplified core-plus-ring model, while the rings frequently extend across its unstable interval. The slightly bluer core colours, lower concentrations, and lower Sérsic indices suggest a possible secular contribution, but the compact, dense cores imply more complex structural assembly than a simple diffuse-pseudobulge origin. The high central fraction may favour gas retention and ring survival by reducing satellite-specific environmental processing. The diversity of ring properties nevertheless leaves room for multiple formation pathways.
ER -