The impact of hot mode accretion and angular momentum conservation on metallicity gradients of galactic discs
Abstract
The hot circumgalactic medium (CGM) of a galaxy inevitably rotates more slowly than the cold gas in the disc it surrounds, due to a higher pressure support against gravity. If it accretes vertically onto the disc, angular momentum conservation leads to radial flows, advection of metals inwards and the steepening of a metallicity gradient. The observed gradient hence carries information on the kinematics of the accreting gas. Previous models built on this premise parametrised the angular momentum mismatch as a simple function of radius, constant in time, rather than derived from the properties of the CGM itself. Here, we present a semi-analytic chemical evolution model of a galaxy with a cosmologically motivated evolution, a self-consistent and time-evolving potential and an isothermal rotating CGM. The model includes inside-out formation and the radial flows induced both by the deepening of the potential well (acting on gas and stars) and by accretion, following their combined effect on the gas-phase metallicity gradient over cosmic time. We use a Bayesian framework to fit simultaneously the structural properties and metallicity gradient of a galaxy, inferring both the required inside-out growth and the CGM temperature needed to drive the required radial flows and abundance gradient. Fitting our model to the Milky Way, we find a mild preference for a subvirial corona (TCGM/T200=0.82+0.44−0.38), in mild tension with observations, and we discuss possible resolutions. The predicted CGM rotation velocity lies between ~100-160 km/s at the present time and is substantially lower at earlier epochs. We further recover an evolution of the gradient over the past ~8Gyr consistent with observations. Our approach is not restricted to the Milky Way and can be directly applied to external galaxies, offering a new handle to constrain hot mode accretion onto galactic discs.
Related
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- Vertical gradients of Galactic rotation from Gaia: The limiting-cone and comparison models
- The JWST/PASSAGE Survey: Metallicity Radial Gradients in Emission-Line Galaxy Pairs at Cosmic Noon with NIRISS
- Cepheid Metallicity in the Leavitt Law (C-MetaLL) survey: X First spectroscopic characterization of Galactic Type II Cepheids and calibration of the Period-Wesenheit-Metallicity relations
BibTeX
@misc{friske2026impact,
title = {{The impact of hot mode accretion and angular momentum conservation on metallicity gradients of galactic discs}},
author = {Jennifer K. S. Friske and Filippo Fraternali and Gabriele Pezzulli},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.31144},
eprint = {2608.31144},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.31144},
}
RIS
TY - UNPB
TI - The impact of hot mode accretion and angular momentum conservation on metallicity gradients of galactic discs
AU - Jennifer K. S. Friske
AU - Filippo Fraternali
AU - Gabriele Pezzulli
PY - 2026
DA - 2026/08/31
PB - arXiv
DO - 10.48550/arxiv.2608.31144
UR - https://arxiv.org/abs/2608.31144
AB - The hot circumgalactic medium (CGM) of a galaxy inevitably rotates more slowly than the cold gas in the disc it surrounds, due to a higher pressure support against gravity. If it accretes vertically onto the disc, angular momentum conservation leads to radial flows, advection of metals inwards and the steepening of a metallicity gradient. The observed gradient hence carries information on the kinematics of the accreting gas. Previous models built on this premise parametrised the angular momentum mismatch as a simple function of radius, constant in time, rather than derived from the properties of the CGM itself. Here, we present a semi-analytic chemical evolution model of a galaxy with a cosmologically motivated evolution, a self-consistent and time-evolving potential and an isothermal rotating CGM. The model includes inside-out formation and the radial flows induced both by the deepening of the potential well (acting on gas and stars) and by accretion, following their combined effect on the gas-phase metallicity gradient over cosmic time. We use a Bayesian framework to fit simultaneously the structural properties and metallicity gradient of a galaxy, inferring both the required inside-out growth and the CGM temperature needed to drive the required radial flows and abundance gradient. Fitting our model to the Milky Way, we find a mild preference for a subvirial corona (T_CGM/T_200=0.82^+0.44_−0.38), in mild tension with observations, and we discuss possible resolutions. The predicted CGM rotation velocity lies between ~100-160 km/s at the present time and is substantially lower at earlier epochs. We further recover an evolution of the gradient over the past ~8Gyr consistent with observations. Our approach is not restricted to the Milky Way and can be directly applied to external galaxies, offering a new handle to constrain hot mode accretion onto galactic discs.
ER -