The nature of CR7 revealed with MUSE: a young starburst powering extended Lyman-$\alpha$ emission at z=6.6

Abstract

CR7 is among the most luminous Lyman-$\alpha$ emitters (LAEs) known at $z=6.6$ and consists of at least three UV components that are surrounded by Lyman-$\alpha$ (Ly$\alpha$) emission. Previous studies have suggested that it may host an extreme ionising source. Here, we present deep integral field spectroscopy of CR7 with VLT/MUSE. We measure extended emission with a similar halo scale length as typical LAEs at $z\approx 5$. CR7's Ly$\alpha$ halo is clearly elongated along the direction connecting the multiple components, likely tracing the underlying gas distribution. The Ly$\alpha$ emission originates almost exclusively from the brightest UV component, but we also identify a faint kinematically distinct Ly$\alpha$ emitting region nearby a fainter component. Combined with new near-infrared data, the MUSE data show that the rest-frame Ly$\alpha$ equivalent width (EW) is $\approx 100$ Å. This is a factor four higher than the EW measured in low-redshift analogues with carefully matched Ly$\alpha$ profiles (and thus arguably HI column density), but this EW can plausibly be explained by star formation. Alternative scenarios requiring AGN powering are also disfavoured by the narrower and steeper Ly$\alpha$ spectrum and much smaller IR to UV ratio compared to obscured AGN in other Ly$\alpha$ blobs. CR7's Ly$\alpha$ emission, while extremely luminous, resembles the emission in more common LAEs at lower redshifts very well and is likely powered by a young metal poor starburst.

Main text 16 pages, 9 figures. Accepted for publication by MNRAS

References in corpus (28)

• The NumPy array: a structure for efficient numerical computation
• The MUSE second-generation VLT instrument
• UltraVISTA: a new ultra-deep near-infrared survey in COSMOS
• The Data Processing Pipeline for the MUSE Instrument
• The MUSE Hubble Ultra Deep Field Survey: I. Survey description, data reduction and source detection
• Using Lyman-alpha to detect galaxies that leak Lyman continuum
• Imfit: A Fast, Flexible New Program for Astronomical Image Fitting
• The First Hyper-Luminous Infrared Galaxy Discovered by WISE
• The Ly-alpha Properties of Faint Galaxies at z2-3 with Systemic Redshifts and Velocity Dispersions from Keck-MOSFIRE
• Identification of the brightest Lyα emitters at z=6.6: implications for the evolution of the luminosity function in the re-ionisation era
• The ALPINE-ALMA [CII] survey: Star-formation-driven outflows and circumgalactic enrichment in the early Universe
• Diffuse Lyman-alpha Halos around Galaxies at z=2.2-6.6: Implications for Galaxy Formation and Cosmic Reionization
• ALMA uncovers the [CII] emission and warm dust continuum in a z = 8.31 Lyman break galaxy
• A spectroscopic search for AGN activity in the reionization era
• The large and small scale properties of the intergalactic gas in the Slug Ly-alpha nebula revealed by MUSE HeII emission observations
• Are high redshift Galaxies hot? - Temperature of z > 5 Galaxies and Implications on their Dust Properties
• ALMA reveals metals yet no dust within multiple components in CR7
• The MUSE Hubble Ultra Deep Field Survey XIII. Spatially resolved spectral properties of Lyman alpha haloes around star-forming galaxies at z > 3
• Spectroscopic properties of luminous Lyman-α emitters at $z\approx 6-7$ and comparison to the Lyman-break population
• Elevated ionizing photon production efficiency in faint high-equivalent-width Lyman-alpha emitters
• Starbursting [O III] emitters and quiescent [C II] emitters in the reionization era
• The MUSE Hubble Ultra Deep Field Survey VIII : Extended Lyman-alpha haloes around high-redshift star-forming galaxies
• Outflows and extended [CII] halos in high redshift galaxies
• Constraining Lyman-alpha spatial offsets at $3<z<5.5$ from VANDELS slit spectroscopy
• ALMA observations of Lyman-alpha Blob 1: halo sub-structure illuminated from within
• Deciphering Lyman $\alpha$ blob 1 with deep MUSE observations
• The MUSE Data Reduction Pipeline: Status after Preliminary Acceptance Europe
• Small-scale Intensity Mapping: Extended Halos as a Probe of the Ionizing Escape Fraction and Faint Galaxy Populations during Reionization

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