KBSS-InCLOSE II: First Detailed Insights on the Inner CGM of Low-Mass z∼2.3 Galaxies
Abstract
We present results from an extension to the Keck Baryonic Structure Survey (KBSS) that focuses on the Inner Circumgalactic Medium (CGM) of QSO Line Of Sight Emitting galaxies at z∼2.3 (InCLOSE). We analyze two low-mass galaxies log(M* / M⊙) ≤ 9 that are within small a projected distance of a QSO Dtran ≤ 50 kpc (Dtran /Rvir ≤ 0.75). One galaxy is detected as a bright Lyman- Emitter with Keck/KCWI (confirmed with follow-up Keck/MOSFIRE spectra), and the other as a serendipitous line emitter with Keck/MOSFIRE. Both galaxies have nebular and morphological properties consistent with those of typical low-mass z∼2.3 star-forming galaxies. Analysis of their CGM absorption as seen with Keck/HIRES spectra of the background QSOs shows no detections of low-ionization metal absorption (low-ions; e.g., Si II), ubiquitous detections of intermediate- (e.g., C IV) and high-ions (O VI), kinematically complex absorption (≥7 components per galaxy halo) spread over |Δv|± 150 km s−1, and no unambiguously unbound gas is detected in either galaxy halo. We analyze the thermal properties of a subset of CGM components, finding that the majority (6/10) have temperatures consistent with heating from the metagalactic UV background (log(T/K)med=4.0) while the remainder possess short-lived, intermediate temperature gas that would require additional heating or rapid replenishment (4.6 ≤ log(T/K) ≤ 5.1), the internal energy of these absorbers are dominated by thermal broadening, their internal (turbulent) velocities are all subsonic, while their motions through the halo are likely supersonic. These results hint that the z2.3 CGM changes with stellar mass in terms of kinematic complexity and unbound gas fraction, while thermal properties remain similar.
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BibTeX
@misc{nunezcravin2026kbssinclose,
title = {{KBSS-InCLOSE II: First Detailed Insights on the Inner CGM of Low-Mass $z\sim2.3$ Galaxies}},
author = {Evan Haze Nunez-Cravin and Charles C. Steidel and Gwen C. Rudie and Evan N. Kirby and Charis M. Hall and Nikolaus Z. Prusinski and Zhuyun Zhuang and Yuanze Ding and Alice E. Shapley and Ryan F. Trainor},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.30834},
eprint = {2609.30834},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.30834},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - KBSS-InCLOSE II: First Detailed Insights on the Inner CGM of Low-Mass z∼2.3 Galaxies
AU - Evan Haze Nunez-Cravin
AU - Charles C. Steidel
AU - Gwen C. Rudie
AU - Evan N. Kirby
AU - Charis M. Hall
AU - Nikolaus Z. Prusinski
AU - Zhuyun Zhuang
AU - Yuanze Ding
AU - Alice E. Shapley
AU - Ryan F. Trainor
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.30834
UR - https://arxiv.org/abs/2609.30834
AB - We present results from an extension to the Keck Baryonic Structure Survey (KBSS) that focuses on the Inner Circumgalactic Medium (CGM) of QSO Line Of Sight Emitting galaxies at z∼2.3 (InCLOSE). We analyze two low-mass galaxies log(M_* / M_⊙) ≤ 9 that are within small a projected distance of a QSO D_tran ≤ 50 kpc (D_tran /R_vir ≤ 0.75). One galaxy is detected as a bright Lyman- Emitter with Keck/KCWI (confirmed with follow-up Keck/MOSFIRE spectra), and the other as a serendipitous line emitter with Keck/MOSFIRE. Both galaxies have nebular and morphological properties consistent with those of typical low-mass z∼2.3 star-forming galaxies. Analysis of their CGM absorption as seen with Keck/HIRES spectra of the background QSOs shows no detections of low-ionization metal absorption (low-ions; e.g., Si II), ubiquitous detections of intermediate- (e.g., C IV) and high-ions (O VI), kinematically complex absorption (≥7 components per galaxy halo) spread over |Δv|± 150 km s^−1, and no unambiguously unbound gas is detected in either galaxy halo. We analyze the thermal properties of a subset of CGM components, finding that the majority (6/10) have temperatures consistent with heating from the metagalactic UV background (log(T/K)_med=4.0) while the remainder possess short-lived, intermediate temperature gas that would require additional heating or rapid replenishment (4.6 ≤ log(T/K) ≤ 5.1), the internal energy of these absorbers are dominated by thermal broadening, their internal (turbulent) velocities are all subsonic, while their motions through the halo are likely supersonic. These results hint that the z2.3 CGM changes with stellar mass in terms of kinematic complexity and unbound gas fraction, while thermal properties remain similar.
ER -