Abstract

We study the kinematics of the interstellar medium (ISM) viewed “down the barrel” in 20 gravitationally lensed galaxies during cosmic noon (z = 1.5-3.5). We use moderate-resolution spectra (R ∼ 4000) from Keck’s Echellette Spectrograph and Imager and Magellan/MagE to spectrally resolve the ISM absorption in these galaxies into ∼10 independent elements and use double Gaussian fits to quantify the velocity structure of the gas. We find that the bulk motion of gas in this galaxy sample is outflowing, with average velocity centroid v cent = − 141 km s−1 (±111 km s−1 scatter) measured with respect to the systemic redshift. A total of 16 out of the 20 galaxies exhibit a clear positive skewness, with a blueshifted tail extending to ∼ −500 km s−1. We examine scaling relations in outflow velocities with galaxy stellar mass and star formation rate, finding correlations consistent with a momentum-driven wind scenario. Our measured outflow velocities are also comparable to those reported for FIRE-2 and TNG50 cosmological simulations at similar redshift and galaxy properties. We also consider implications for interpreting results from lower-resolution spectra. We demonstrate that while velocity centroids are accurately recovered, the skewness, velocity width, and probes of high-velocity gas (e.g., v 95) are subject to large scatter and biases at lower resolution. We find that R ≳ 1700 is required for accurate results for the gas kinematics of our sample. This work represents the largest available sample of well-resolved outflow velocity structure at z > 2 and highlights the need for good spectral resolution to recover accurate properties.

Document Type

Article

Publication Date

2023

Notes/Citation Information

© 2023. The Author(s). Published by the American Astronomical Society.

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.

Digital Object Identifier (DOI)

https://doi.org/10.3847/1538-4357/acf462

Funding Information

This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. Some of the data presented herein were 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 the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank Jane Rigby and the MEGaSaURA team for making their spectra publicly available. T.J. and K.V.G.C. gratefully acknowledge support from the Gordon and Betty Moore Foundation through grant GBMF8549, from the National Science Foundation through grant AST- 2108515, and from a Deanʼs Faculty Fellowship. Support for this work was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51469.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. R.S.E. acknowledges funding from the European Research Council under the European Union Horizon 2020 research and innovation program (grant agreement No. 669253). This research was supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO3D) through project number CE170100013. 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.

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