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

Abstract

We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift $z\:^{<}_{\sim }\:1$ 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 zabs < 1. We report five new LLSs of $\log \, N({\rm {H\,{I}}})/\rm {{\rm cm^{-2}}}\:^{>}_{\sim }\:17.2$ over a total redshift survey pathlength of Δ zLL = 9.3, and a number density of $n(z)=0.43_{-0.18}^{+0.26}$. Considering all absorbers with $\log \, N({\rm {H\,{I}}})/\rm {{\rm cm^{-2}}}>16.5$ leads to $n(z)=1.08_{-0.25}^{+0.31}$ at zabs < 1. All LLSs exhibit a multi-component 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 $d\:^{<}_{\sim }\:300$ 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/disk, 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 ≈0.01 L* to ≈3 L*. Our study shows that LLSs originate in a variety of galaxy environments and trace gaseous structures with a broad range of metallicities.

Pair lines of sight observations of multiphase gas bearing O vi in a galaxy environment

“…11, and the remaining at 1 Mpc. The presence of several galaxies within narrow projected positions and radial velocities indicates that the lines of sight are probing different regions of a galaxy overdensity such as a group or a cluster, with the absorption possibly arising in the CGM or the intragroup/cluster medium, consistent with what has been found for optically thick gas (Muzahid et al 2017;Manuwal et al 2019;Pradeep et al 2019;Chen et al 2020).…”

MUSE Analysis of Gas around Galaxies (MAGG) – II: metal-enriched halo gas around z ∼ 1 galaxies

“…Lan (2020) also find no redshift evolution over 0.4 < z < 1.3 in the covering fraction of Mg II absorbers with 0.4 < W Mg II r <1 Å, which is similar to the W Mg II r distribution of our sample, although they do find that strong absorbers (W Mg II r >1 Å) show significant redshift evolution in their covering fraction around both star-forming and passive galaxies. Such trends in redshift evolution of the cool CGM will be soon better explored by ongoing surveys such as QSAGE (Bielby et al 2019) and CUBS (Chen et al 2020).…”

“…Deeper surveys like that being carried out in the MUDF (Fossati et al 2019b) will push such studies to lower mass galaxies. Further, NIR spectroscopic coverage of our fields or in fields part of recent Hubble Space Telescope surveys (Bielby et al 2019;Chen et al 2020) will help to extend the study of cool gas and of environmental effects on the metals in CGM to higher redshifts.…”

The Cosmic Ultraviolet Baryon Survey (CUBS) – III. Physical properties and elemental abundances of Lyman-limit systems at z &lt; 1

“…CUBS is based on a large Hubble Space Telescope (HST) Cycle 25 General Observer Program (GO-CUBS; PID = 15163; PI: Chen) to obtain high-quality FUV spectra of 15 UV bright QSOs. Our survey aims to map diffuse gas at z < ∼ 1 using QSO absorption-line spectroscopy, which is complemented by deep galaxy survey data (Chen et al 2020). CUBS will establish a large sample of galaxies and absorbers at z < 1, and enable systematic studies of the co-evolution of galaxies and their CGM at an epoch of precipitous decline in the cosmic star-formation rate density (SFRD), offering critical insights into how the complex interplay of gas accretion and outflows govern the mass assembly of galaxies over cosmic time.…”