Metallicity Dilution Without a Detectable Star Formation Difference in Morphologically Disturbed versus Quiet Early-Type Galaxies
- 1CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories 1 , Beijing, 100101 ,
Abstract
We identify a population of diluted early-type galaxies (ETGs) with gas-phase metallicities significantly below the local mass-metallicity relation. After matching to a sample of undiluted galaxies matched in stellar mass and redshift, we show that the metallicity deficit remains highly significant. Morphological classification does not provide statistically significant evidence for different star-formation responses: disturbed systems exhibit both metallicity dilution and enhanced star formation, while quiet diluted ETGs show substantial metallicity deficits but the sample too small to detect a similar enhancement at high significance. A simple gas-mixing model shows that the observed metallicity deficit can be reproduced through the accretion of metal-poor gas, requiring an accreted gas mass of only ~7% of the stellar mass. We suggest that metal-poor gas accretion is a common origin of diluted ETGs, while whether their subsequent star-formation response depends on the dynamical state of the host galaxy remains an open question.
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BibTeX
@article{wu2026metallicity,
title = {{Metallicity Dilution Without a Detectable Star Formation Difference in Morphologically Disturbed versus Quiet Early-Type Galaxies}},
author = {Yu-Zhong Wu},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = nov,
doi = {10.1093/mnras/stag2103},
url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2103/9012714},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Metallicity Dilution Without a Detectable Star Formation Difference in Morphologically Disturbed versus Quiet Early-Type Galaxies
AU - Yu-Zhong Wu
PY - 2026
DA - 2026/11/04
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag2103
UR - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2103/9012714
AB - We identify a population of diluted early-type galaxies (ETGs) with gas-phase metallicities significantly below the local mass-metallicity relation. After matching to a sample of undiluted galaxies matched in stellar mass and redshift, we show that the metallicity deficit remains highly significant. Morphological classification does not provide statistically significant evidence for different star-formation responses: disturbed systems exhibit both metallicity dilution and enhanced star formation, while quiet diluted ETGs show substantial metallicity deficits but the sample too small to detect a similar enhancement at high significance. A simple gas-mixing model shows that the observed metallicity deficit can be reproduced through the accretion of metal-poor gas, requiring an accreted gas mass of only ~7% of the stellar mass. We suggest that metal-poor gas accretion is a common origin of diluted ETGs, while whether their subsequent star-formation response depends on the dynamical state of the host galaxy remains an open question.
SN - 0035-8711
SN - 1365-2966
ER -