Lyman Continuum Galaxy Candidates in COSMOS

Creators: Prichard, Laura J.; Rafelski, Marc; Cooke, Jeff; Meštrić, Uros; Bassett, Robert; Ryan-Weber, Emma V.; Sunnquist, Ben; Alavi, Anahita; Hathi, Nimish; Wang, Xin; Revalski, Mitchell; Bajaj, Varun; O'Meara, John M.; Spitler, Lee

Abstract

Star-forming galaxies are the sources likely to have reionized the universe. As we cannot observe them directly due to the opacity of the intergalactic medium at z ≳ 5, we study z ∼ 3–5 galaxies as proxies to place observational constraints on cosmic reionization. Using new deep Hubble Space Telescope rest-frame UV F336W and F435W imaging (30 orbits, ∼40 arcmin2, ∼29–30 mag depth at 5σ), we attempt to identify a sample of Lyman continuum galaxies (LCGs). These are individual sources that emit ionizing flux below the Lyman break (f_(esc)) of ionizing sources. We compile a comprehensive parent sample that does not rely on the Lyman-break technique for redshifts. We present three new spectroscopic candidates at z ∼ 3.7–4.4 and 32 new photometric candidates. The high-resolution multiband HST imaging and new Keck/Low Resolution Imaging Spectrometer (LRIS) redshifts make these promising spectroscopic LCG candidates. Using both a traditional and a probabilistic approach, we find that the most likely f_(esc) values for the three spectroscopic LCG candidates are >100% and therefore not physical. We are unable to confirm the true nature of these sources with the best available imaging and direct blue Keck/LRIS spectroscopy. More spectra, especially from the new class of 30 m telescopes, will be required to build a statistical sample of LCGs to place firm observational constraints on cosmic reionization.

Additional Information

© 2022. 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. Received 2021 July 2; revised 2021 October 8; accepted 2021 October 13; published 2022 January 5. We thank the anonymous reviewer for a helpful report. This research is based on observations made with the NASA/ESA HST obtained from the STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 526555. These observations are associated with program ID 15100 (PI: Cooke), and we acknowledge financial support for this work from HST. We also acknowledge some additional support from HST program ID 15647 (PI: Teplitz) for work related to the final data calibrations presented here. This work is also based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST. This work was supported by three NASA Keck PI Data Awards (2018B_N188 and 2019B_N010, PI: Rafelski; and 2020B_N168, PI: Prichard), administered by the NASA Exoplanet Science Institute. This work was also made possible with funding from STScI's Director's Discretionary Research Funding (grant ID D0001.82500). Part of this research was funded by the Australian Research Council Centre of Excellence for All-sky Astrophysics in 3 Dimensions (ASTRO-3D), CE170100013, the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), CE110001020, and the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav), CE170100004. The data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to NASA 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. This research made use of Montage. It is funded by the National Science Foundation under grant No. ACI-1440620 and was previously funded by NASA's Earth Science Technology Office, Computation Technologies Project, under cooperative agreement No. NCC5-626 between NASA and the California Institute of Technology. This paper is based in part on data collected at the Subaru Telescope and retrieved from the HSC data archive system, which is operated by the Subaru Telescope and Astronomy Data Center (ADC) at the National Astronomical Observatory of Japan. Data analysis was in part carried out with the cooperation of the Center for Computational Astrophysics (CfCA), National Astronomical Observatory of Japan. Facilities: HST(WFC3, ACS), Keck:I (LRIS), Subaru(HSC). Software: astropy (Astropy Collaboration et al. 2013), autoslit, calwf3 v3.6.0 (Anderson 2020; Anderson et al. 2021), DrizzlePac (Gonzaga et al. 2012; Hoffmann et al. 2021), IRAF, Montage, photutils, and codes from R. Bassett (on GitHub), L. Prichard (on GitHub), M. Revalski (on GitHub), and B. Sunnquist (on GitHub).

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