The 1.6 μm H− bump as a diagnostic of TP-AGB contributions and recent quenching. I. Insights from stellar population models
Abstract
The 1.6 μm H− bump arises from a minimum in the opacity of the negative hydrogen ion in cool stellar atmospheres. Although it is recognized as a common feature in galaxy spectra, its potential for studying stellar populations and recent quenching remains little explored. Its enhancement at intermediate ages is strong in some stellar population models with substantial thermally pulsing asymptotic giant branch (TP-AGB) contributions but weak or absent in others. This variation makes the feature both a potential age diagnostic and a source of model uncertainty. We use models based on the X-shooter Spectral Library (XSL) and Flexible Stellar Population Synthesis (FSPS) to examine what drives this behavior and what it can reveal about quenching. Controlled FSPS experiments show that the H− bump depends on both the amount of TP-AGB light and the stellar template used to represent it. The adopted XSL and TP-AGB-on FSPS models predict a transient enhancement following rapid quenching, with a different age response from optical spectral features. Combining these diagnostics can therefore provide additional information about recent quenching, although the interpretation depends on the population model and star-formation history. An illustrative comparison with existing JWST spectra shows that models including TP-AGB contributions can describe the observed H− region reasonably well. These results motivate further use of the H− bump to test TP-AGB prescriptions and investigate quenching with current and forthcoming observations.
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BibTeX
@misc{lu2026bump,
title = {{The 1.6 $μ\mathrmm$ $\rmH^-$ bump as a diagnostic of TP-AGB contributions and recent quenching. I. Insights from stellar population models}},
author = {Pengjun Lu and Song Huang and Shiying Lu and Meng Gu and Li Shen and Cheng Li},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.35969},
eprint = {2609.35969},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.35969},
}
RIS
TY - UNPB
TI - The 1.6 μm H^− bump as a diagnostic of TP-AGB contributions and recent quenching. I. Insights from stellar population models
AU - Pengjun Lu
AU - Song Huang
AU - Shiying Lu
AU - Meng Gu
AU - Li Shen
AU - Cheng Li
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.35969
UR - https://arxiv.org/abs/2609.35969
AB - The 1.6 μm H^− bump arises from a minimum in the opacity of the negative hydrogen ion in cool stellar atmospheres. Although it is recognized as a common feature in galaxy spectra, its potential for studying stellar populations and recent quenching remains little explored. Its enhancement at intermediate ages is strong in some stellar population models with substantial thermally pulsing asymptotic giant branch (TP-AGB) contributions but weak or absent in others. This variation makes the feature both a potential age diagnostic and a source of model uncertainty. We use models based on the X-shooter Spectral Library (XSL) and Flexible Stellar Population Synthesis (FSPS) to examine what drives this behavior and what it can reveal about quenching. Controlled FSPS experiments show that the H^− bump depends on both the amount of TP-AGB light and the stellar template used to represent it. The adopted XSL and TP-AGB-on FSPS models predict a transient enhancement following rapid quenching, with a different age response from optical spectral features. Combining these diagnostics can therefore provide additional information about recent quenching, although the interpretation depends on the population model and star-formation history. An illustrative comparison with existing JWST spectra shows that models including TP-AGB contributions can describe the observed H^− region reasonably well. These results motivate further use of the H^− bump to test TP-AGB prescriptions and investigate quenching with current and forthcoming observations.
ER -