Tracing Interstellar Gas in Quiescent Galaxies Using Na I D and Ca II H&K Absorption
Abstract
For over two decades, Na I D (λλ5891.58, 5897.56 Å) absorption has been the primary optical tracer of cool, neutral gas in galaxies. In contrast, Ca II H&K (λλ3934.78, 3969.59 Å), which traces both neutral and ionized gas, has been comparatively unexplored. Here, we present a comparative study of the Na I D and Ca II H&K interstellar absorption lines using spatially resolved MaNGA IFU spectroscopy of 140 red geyser galaxies (local quiescent systems hosting low-luminosity AGN with bisymmetric ionized outflows) and a control sample of 140 quiescent galaxies. Using Gaussian fits to the Na I D and Ca II K lines, we measure gas velocity and dispersion. We find that the Ca II reservoirs are up to ~ 6 times larger in area, twice as radially extended, and have ~ 1.7 - 1.8x broader line widths than Na I D. Furthermore, Na I D shows a direct dependence on dust reservoir size, but the correlation vanishes for Ca II. In only ~ 20% of galaxies do the Na I D detections extend beyond dust regions, but this fraction jumps to ~70% for Ca II. Using these findings, we argue that dust plays a significant role in shielding Na I D from ionizing radiation, whereas Ca II, with its higher ionization potential, is not as dependent on shielding and can more easily survive beyond regions of dust. Na I D and Ca II trace distinct gas components, and studying both together provides a more complete picture of gas flows in galaxies.
Related
- Evolution of the morphology-density and morphology-mass relations of quiescent galaxies at 0.5 {2}lt;z<$ 2.5 in the COSMOS-Web survey
- The Role of Environment in Shaping the Assembly Timelines of Massive Quiescent Galaxies at Cosmic Noon
- The Stellar Populations of Two Quiescent Low Surface Brightness Dwarf Galaxies in Low Density Environments
- Unveiling the hot interstellar medium in nearby galaxies with eROSITA
- Tracing gas outflows in molecular gas-rich galaxies with the SKA
BibTeX
@misc{moghni2026tracing,
title = {{Tracing Interstellar Gas in Quiescent Galaxies Using Na I D and Ca II H&K Absorption}},
author = {Arian Moghni and Timothy M. Heckman and Namrata Roy and Kyle B. Westfall and Kevin Bundy and Kate H. R. Rubin},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.23288},
eprint = {2609.23288},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.23288},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Tracing Interstellar Gas in Quiescent Galaxies Using Na I D and Ca II H&K Absorption
AU - Arian Moghni
AU - Timothy M. Heckman
AU - Namrata Roy
AU - Kyle B. Westfall
AU - Kevin Bundy
AU - Kate H. R. Rubin
PY - 2026
DA - 2026/09/20
PB - arXiv
DO - 10.48550/arxiv.2609.23288
UR - https://arxiv.org/abs/2609.23288
AB - For over two decades, Na I D (λλ5891.58, 5897.56 Å) absorption has been the primary optical tracer of cool, neutral gas in galaxies. In contrast, Ca II H&K (λλ3934.78, 3969.59 Å), which traces both neutral and ionized gas, has been comparatively unexplored. Here, we present a comparative study of the Na I D and Ca II H&K interstellar absorption lines using spatially resolved MaNGA IFU spectroscopy of 140 red geyser galaxies (local quiescent systems hosting low-luminosity AGN with bisymmetric ionized outflows) and a control sample of 140 quiescent galaxies. Using Gaussian fits to the Na I D and Ca II K lines, we measure gas velocity and dispersion. We find that the Ca II reservoirs are up to ~ 6 times larger in area, twice as radially extended, and have ~ 1.7 - 1.8x broader line widths than Na I D. Furthermore, Na I D shows a direct dependence on dust reservoir size, but the correlation vanishes for Ca II. In only ~ 20% of galaxies do the Na I D detections extend beyond dust regions, but this fraction jumps to ~70% for Ca II. Using these findings, we argue that dust plays a significant role in shielding Na I D from ionizing radiation, whereas Ca II, with its higher ionization potential, is not as dependent on shielding and can more easily survive beyond regions of dust. Na I D and Ca II trace distinct gas components, and studying both together provides a more complete picture of gas flows in galaxies.
ER -