Abstract
We have discovered a 300 kpc-wide giant Lyman-α (Lyα) nebula centered on the massive galaxy group RO-1001 at z = 2.91 in the Cosmic Evolution Survey field. Keck Cosmic Web Imager observations reveal three cold gas filaments converging into the center of the potential well of its ∼4 × 1013 M⊙ dark matter halo, hosting 1200 M⊙ yr−1 of star formation as probed by Atacama Large Millimeter Array and NOrthern Extended Millimeter Array observations. The nebula morphological and kinematics properties and the prevalence of blueshifted components in the Lyα spectra are consistent with a scenario of gas accretion. The upper limits on active galactic nuclei activity and overall energetics favor gravity as the primary Lyα powering source and infall as the main source of gas flows to the system. Although interpretational difficulties remain, with outflows and likely also photoionization with ensuing recombination still playing a role, this finding provides arguably an ideal environment to quantitatively test models of cold gas accretion and galaxy feeding inside an actively star-forming massive halo at high redshift.
Highlights
A fundamental phenomenon required to explain the evolution of massive galaxies at high redshifts is the efficient accretion of cold gas streaming along filaments, surviving the shocks at the virial radii of their massive halos and delivering the required fuel to galaxies (Dekel et al 2009; Kereš et al 2005)
RO-1001 was selected in the Cosmic Evolution Survey (COSMOS) two-square-degree field as a 12σ overdensity of optically faint radio sources centered at RA 10:01:23.064 and Dec 2:20:04.86, following a recently proposed technique (Daddi et al 2017): it was found to contain three Very Large Array (VLA) detections with S 3 GHz > 30 μJy and zphot > 2.5 within a radius of 10 (80 kpc; proper scales are used throughout the paper), which is the size of a massive halo core (Strazzullo et al 2013; Wang et al 2016)
The classic expectation would be collisionally excited Lyα from the cold gas dissipating kinetic energy acquired via the gravitational energy
Summary
A fundamental phenomenon required to explain the evolution of massive galaxies at high redshifts is the efficient accretion of cold gas streaming along filaments, surviving the shocks at the virial radii of their massive halos and delivering the required fuel to galaxies (Dekel et al 2009; Kereš et al 2005). Among the great advantages of integral field spectroscopy, as provided routinely by the multi-unit spectroscopic explorer (MUSE; Bacon et al 2010) and KCWI (Morrissey et al 2018), and as opposed to earlier narrow-band imaging attempts, is the potential to unveil the kinematics and spectral properties of the Lyα emission that, keeping in mind the uncertainties linked to resonant scattering effects, can provide valuable diagnostics on the presence of accretion (see, e.g., Ao et al 2020) As part of these efforts, we used KCWI to search for redshifted Lyα in RO-1001, a massive group of galaxies at z = 2.91 that is currently our best-studied target with the deepest and widest observations, which we present in this work. We adopt a standard cosmology and a Chabrier initial mass function (IMF)
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