The baryonic mass-size relation of galaxies. I. A dichotomy in star-forming galaxy disks
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| Format: | Preprint |
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2025
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| _version_ | 1866914104476696576 |
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| author | Hua, Zichen Lelli, Federico Di Teodoro, Enrico McGaugh, Stacy Schombert, James |
| author_facet | Hua, Zichen Lelli, Federico Di Teodoro, Enrico McGaugh, Stacy Schombert, James |
| contents | The mass-size relations of galaxies are generally studied considering only stars or only gas separately. Here we study the baryonic mass-size relation of galaxies from the SPARC database, using the total baryonic mass ($M_{\rm bar}$) and the baryonic half-mass radius ($R_{\rm 50, bar}$). We find that SPARC galaxies define two distinct sequences in the $M_{\rm bar} - R_{\rm 50, bar}$ plane: one that formed by high-surface-density (HSD), star-dominated, Sa-to-Sc galaxies, and one by low-surface-density (LSD), gas-dominated, Sd-to-dI galaxies. The $M_{\rm bar} - R_{\rm 50, bar}$ relation of LSD galaxies has a slope close to 2, pointing to a constant average surface density, whereas that of HSD galaxies has a slope close to 1, indicating that less massive spirals are progressively more compact. Our results point to the existence of two types of star-forming galaxies that follow different evolutionary paths: HSD disks are very efficient in converting gas into stars, perhaps thanks to the efficient formation of non-axisymmetric structures (bars and spiral arms), whereas LSD disks are not. The HSD-LSD dichotomy is absent in the baryonic Tully-Fisher relation ($M_{\rm bar}$ versus flat circular velocity $V_{\rm f}$) but moderately seen in the angular-momentum relation (approximately $M_{\rm bar}$ versus $V_{\rm f}\times R_{\rm 50, bar}$), so it is driven by variations in $R_{\rm 50, bar}$ at fixed $M_{\rm bar}$. This fact suggests that the baryonic mass-size relation is the most effective empirical tool to distinguish different galaxy types and study their evolution. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2510_17770 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The baryonic mass-size relation of galaxies. I. A dichotomy in star-forming galaxy disks Hua, Zichen Lelli, Federico Di Teodoro, Enrico McGaugh, Stacy Schombert, James Astrophysics of Galaxies The mass-size relations of galaxies are generally studied considering only stars or only gas separately. Here we study the baryonic mass-size relation of galaxies from the SPARC database, using the total baryonic mass ($M_{\rm bar}$) and the baryonic half-mass radius ($R_{\rm 50, bar}$). We find that SPARC galaxies define two distinct sequences in the $M_{\rm bar} - R_{\rm 50, bar}$ plane: one that formed by high-surface-density (HSD), star-dominated, Sa-to-Sc galaxies, and one by low-surface-density (LSD), gas-dominated, Sd-to-dI galaxies. The $M_{\rm bar} - R_{\rm 50, bar}$ relation of LSD galaxies has a slope close to 2, pointing to a constant average surface density, whereas that of HSD galaxies has a slope close to 1, indicating that less massive spirals are progressively more compact. Our results point to the existence of two types of star-forming galaxies that follow different evolutionary paths: HSD disks are very efficient in converting gas into stars, perhaps thanks to the efficient formation of non-axisymmetric structures (bars and spiral arms), whereas LSD disks are not. The HSD-LSD dichotomy is absent in the baryonic Tully-Fisher relation ($M_{\rm bar}$ versus flat circular velocity $V_{\rm f}$) but moderately seen in the angular-momentum relation (approximately $M_{\rm bar}$ versus $V_{\rm f}\times R_{\rm 50, bar}$), so it is driven by variations in $R_{\rm 50, bar}$ at fixed $M_{\rm bar}$. This fact suggests that the baryonic mass-size relation is the most effective empirical tool to distinguish different galaxy types and study their evolution. |
| title | The baryonic mass-size relation of galaxies. I. A dichotomy in star-forming galaxy disks |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2510.17770 |