The Circumgalactic Medium of Extreme Emission Line Galaxies at z∼2: Resolved Spectroscopy and Radiative Transfer Modeling of Spatially Extended Lyα Emission in the KBSS-KCWI Survey

Creators: Erb, Dawn K.; Li 李智, Zhihui 慧¹; Steidel, Charles C.¹; Chen 陈昱, Yuguang 光; Gronke, Max; Strom, Allison L.; Trainor, Ryan F.; Rudie, Gwen C.

1. California Institute of Technology

Abstract

The resonantly scattered Lyα line illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Lyα emission in 12 relatively low-mass (M_⋆ ∼ 10⁹ M_⊙) z ∼ 2 galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Lyα blue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak separation, and trough depth with radius, and broadly reconcile outflow velocities inferred from Lyα and absorption lines. The galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (ICM), whose residual neutral content produces absorption at the systemic redshift. The peak ratio, peak separation, and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the H i column density, and the residual neutral density in the ICM respectively. The azimuthal asymmetries in the line profile further suggest nonradial gas motions at large radii and variations in the H i column density in the outer halos.

Acknowledgement

The authors thank the referee for a detailed and constructive report, and Crystal Martin, Peng Oh, and Tim Heckman for helpful discussions. D.K.E. is supported by the US National Science Foundation (NSF) through Astronomy & Astrophysics grant AST-1909198. C.C.S, Z.L., and Y.C. are supported in part by NSF grant AST-2009278. R.F.T. is a Cottrell Scholar receiving support from the Research Corporation for Science Advancement under grant ID 28289 and from the Pittsburgh Foundation under grant ID UN2021-121482. Some data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. D.K.E. acknowledges in Milwaukee that we are on traditional Potawatomi, Ho-Chunk, and Menominee homeland along the southwest shores of Michigami, North America's largest system of freshwater lakes, where the Milwaukee, Menominee, and Kinnickinnic rivers meet and the people of Wisconsin's sovereign Anishinaabe, Ho-Chunk, Menominee, Oneida, and Mohican nations remain present.

Facility: Keck II (KCWI) - KECK II Telescope.

Software: KCWI DRP²⁸, astropy (Astropy Collaboration et al. 2013, 2018), dynesty (Skilling 2004, 2006; Speagle2020), spectral-cube (Ginsburg et al. 2019), SExtractor (Bertin & Arnouts 1996), cmasher (van der Velden2020), seaborn (Waskom et al. 2020).

Errata

This article is corrected by 2024 ApJ 961 143

Correction: The column headings in Table 3 have been reordered due to a mismatch between the column headers and the data columns. The
data in the table have not changed.

Additional Information

Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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