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The KBSS–KCWI survey: the connection between extended Ly α haloes and galaxy azimuthal angle at z ∼ 2–3

Chen, Yuguang and Steidel, Charles C. and Erb, Dawn K. and Law, David R. and Trainor, Ryan F. and Reddy, Naveen A. and Shapley, Alice E. and Pahl, Anthony J. and Strom, Allison L. and Lamb, Noah R. and Li, Zhihui and Rudie, Gwen C. (2021) The KBSS–KCWI survey: the connection between extended Ly α haloes and galaxy azimuthal angle at z ∼ 2–3. Monthly Notices of the Royal Astronomical Society, 508 (1). pp. 19-43. ISSN 0035-8711. doi:10.1093/mnras/stab2383.

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We present the first statistical analysis of kinematically resolved, spatially extended Lyα emission around z = 2–3 galaxies in the Keck Baryonic Structure Survey (KBSS) using the Keck Cosmic Web Imager (KCWI). Our sample of 59 star-forming galaxies (z_(med) = 2.29) comprises the subset with typical KCWI integration times of ∼5 h and with existing imaging data from the Hubble Space Telescope and/or adaptive optics-assisted integral field spectroscopy. The high-resolution images were used to evaluate the azimuthal dependence of the diffuse Lyα emission with respect to the stellar continuum within projected galactocentric distances of ≲30 proper kpc. We introduce cylindrically projected 2D spectra (CP2D) that map the averaged Lyα spectral profile over a specified range of azimuthal angle, as a function of impact parameter around galaxies. The averaged CP2D spectrum of all galaxies shows clear signatures of Lyα resonant scattering by outflowing gas. We stacked the CP2D spectra of individual galaxies over ranges of azimuthal angle with respect to their major axes. The extended Lyα emission along the galaxy principal axes is statistically indistinguishable, with residual asymmetry of ≤2 per cent (∼2σ) of the integrated Lyα emission. The symmetry implies that the Lyα scattering medium is dominated by outflows in all directions within 30 kpc. Meanwhile, we find that the blueshifted component of Lyα emission is marginally stronger along galaxy minor axes for galaxies with relatively weak Lyα emission. We speculate that this weak directional dependence of Lyα emission becomes discernible only when the Lyα escape fraction is low. These discoveries highlight the need for similar analyses in simulations with Lyα radiative transfer modelling.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Chen, Yuguang0000-0003-4520-5395
Steidel, Charles C.0000-0002-4834-7260
Erb, Dawn K.0000-0001-9714-2758
Law, David R.0000-0002-9402-186X
Trainor, Ryan F.0000-0002-6967-7322
Reddy, Naveen A.0000-0001-9687-4973
Shapley, Alice E.0000-0003-3509-4855
Pahl, Anthony J.0000-0003-4464-4505
Strom, Allison L.0000-0001-6369-1636
Lamb, Noah R.0000-0002-2052-822X
Li, Zhihui0000-0001-5113-7558
Rudie, Gwen C.0000-0002-8459-5413
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. Received: 19 April 2021; Revision received: 14 August 2021; Accepted: 14 August 2021; Published: 19 August 2021. This work has included data from Keck/KCWI (Morrissey et al. 2018), Keck/OSIRIS (Larkin et al. 2006), Keck/MOSFIRE (McLean et al. 2012), Keck/LRIS-B (Steidel et al. 2004), HST/WFC3-IR, and HST/ACS. We appreciate the contribution from the staff of the W. M. Keck Observatory and the Space Telescope Science Institute. The following software packages have been crucial to the results presented: Astropy (Astropy Collaboration 2018), the SciPy and NumPy system (Harris et al. 2020; Virtanen et al. 2020), QFitsView,9 CWITools (O’Sullivan & Chen 2020), Montage,10GALFIT (Peng et al. 2002, 2010), and DrizzlePac. This work has been supported in part by grant AST-2009278 from the US NSF, by NASA through grant HST-GO15287.001, and the JPL/Caltech President’s and Director’s Program (YC, CS). 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. We would like to thank the anonymous referee for providing constructive feedback. We would like to acknowledge Kurt Adelberger, Milan Bogosavljević, Max Pettini, and Rachel Theios for their contribution to the KBSS survey. It is a great pleasure for us to thank Don Neill, Mateusz Matuszewski, Luca Rizzi, Donal O’Sullivan, and Sebastiano Cantalupo for their help in handling the KCWI data, and Cameron Hummels and Max Gronke for insightful discussions. YC would like to acknowledge his grandfather, Chen Yizong, who passed away during the preparation of this manuscript. 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 the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Data Availability: The composite CP2D spectra and the PYTHON program used to generate figures in this article are available upon reasonable request.
Group:Astronomy Department
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
JPL President and Director's FundUNSPECIFIED
Subject Keywords:galaxies: evolution, galaxies: ISM, galaxies: high-redshift
Issue or Number:1
Record Number:CaltechAUTHORS:20210825-184651133
Persistent URL:
Official Citation:Yuguang Chen, (陈昱光), Charles C Steidel, Dawn K Erb, David R Law, Ryan F Trainor, Naveen A Reddy, Alice E Shapley, Anthony J Pahl, Allison L Strom, Noah R Lamb, Zhihui Li, (李智慧), Gwen C Rudie, The KBSS–KCWI survey: the connection between extended Ly α haloes and galaxy azimuthal angle at z ∼ 2–3, Monthly Notices of the Royal Astronomical Society, Volume 508, Issue 1, November 2021, Pages 19–43,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110564
Deposited By: George Porter
Deposited On:30 Aug 2021 14:45
Last Modified:04 Oct 2021 18:00

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