The Cosmic Ultraviolet Baryon Survey (CUBS) - I. Overview and the diverse environments of Lyman limit systems at z < 1

September 2020 • 2020MNRAS.497..498C

Authors • Chen, Hsiao-Wen • Zahedy, Fakhri S. • Boettcher, Erin • Cooper, Thomas M. • Johnson, Sean D. • Rudie, Gwen C. • Chen, Mandy C. • Walth, Gregory L. • Cantalupo, Sebastiano • Cooksey, Kathy L. • Faucher-Giguère, Claude-André • Greene, Jenny E. • Lopez, Sebastian • Mulchaey, John S. • Penton, Steven V. • Petitjean, Patrick • Putman, Mary E. • Rafelski, Marc • Rauch, Michael • Schaye, Joop • Simcoe, Robert A. • Weiner, Benjamin J.

Abstract • We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift z ≲ 1 using absorption-line spectroscopy of 15 UV-bright QSOs with matching deep galaxy survey data. CUBS QSOs are selected based on their NUV brightness to avoid biases against the presence of intervening Lyman limit systems (LLSs) at z_abs < 1. We report five new LLSs of $\log \, N({\mathrm{ H} \,{\small I}})/{{\rm cm^{-2}}}\gtrsim 17.2$ over a total redshift survey path-length of $\Delta \, z_{\mathrm{ LL}}=9.3$ , and a number density of $n(z)=0.43_{-0.18}^{+0.26}$ . Considering all absorbers with $\log \, N({{\mathrm{ H} \,{\small I}}})/{{\rm cm^{-2}}}\gt 16.5$ leads to $n(z)=1.08_{-0.25}^{+0.31}$ at z_abs < 1. All LLSs exhibit a multicomponent structure and associated metal transitions from multiple ionization states such as C II, C III, Mg II, Si II, Si III, and O VI absorption. Differential chemical enrichment levels as well as ionization states are directly observed across individual components in three LLSs. We present deep galaxy survey data obtained using the VLT-MUSE integral field spectrograph and the Magellan Telescopes, reaching sensitivities necessary for detecting galaxies fainter than $0.1\, L_*$ at d ≲ 300 physical kpc (pkpc) in all five fields. A diverse range of galaxy properties is seen around these LLSs, from a low-mass dwarf galaxy pair, a co-rotating gaseous halo/disc, a star-forming galaxy, a massive quiescent galaxy, to a galaxy group. The closest galaxies have projected distances ranging from d = 15 to 72 pkpc and intrinsic luminosities from ${\approx} 0.01\, L_*$ to ${\approx} 3\, L_*$ . Our study shows that LLSs originate in a variety of galaxy environments and trace gaseous structures with a broad range of metallicities.

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Greg Walth

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