The MUSE Hubble Ultra Deep Field Survey - VIII. Extended Lyman-α haloes around high-z star-forming galaxies

By F. Leclercq, R. Bacon, L. Wisotzki, Peter D Mitchell, T. Garel, A. Verhamme, Jérémy Blaizot, T. Hashimoto, E. C. Herenz, Simon Conseil and 10 more. 2017

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We report the detection of extended Ly α haloes around 145 individual star-forming galaxies at redshifts 3 ≤ z ≤ 6 in the Hubble Ultra Deep Field observed with the Multi-Unit Spectroscopic Explorer (MUSE) at ESO-VLT. Our sample consists of continuum-faint (− 15 ≥ M UV ≥ −22) Ly α emitters (LAEs). Using a 2D, two-component (continuum-like and halo) decomposition of Ly α emission assuming circular exponential distributions, we measure scale lengths and luminosities of Ly α haloes. We find that 80% of our objects having reliable Ly α halo measurements show Ly α emission that is significantly more extended than the UV continuum detected by HST (by a factor ≈4 to >20). The median exponential scale length of the Ly α haloes in our sample is ≈4.5 kpc with a few haloes exceeding 10 kpc. By comparing the maximal detected extent of the Ly α emission with the predicted dark matter halo virial radii of simulated galaxies, we show that the detected Ly α emission of our selected sample of Ly α emitters probes a significant portion of the cold circum-galactic medium of these galaxies (>50% in average). This result therefore shows that there must be significant HI reservoirs in the circum-galactic medium and reinforces the idea that Ly α haloes are ubiquitous around high-redshift Ly α emitting galaxies. Our characterization of the Ly α haloes indicates that the majority of the Ly α flux comes from the halo (≈65%) and that their scale lengths seem to be linked to the UV properties of the galaxies (sizes and magnitudes). We do not observe a significant Ly α halo size evolution with redshift, although our sample for z > 5 is very small. We also explore the diversity of the Ly α line profiles in our sample and we find that the Ly α lines cover a large range of full width at half maximum (FWHM) from 118 to 512 km s -1 . While the FWHM does not seem to be correlated to the Ly α scale length, most compact Ly α haloes and those that are not detected with high significance tend to have narrower Ly α profiles ( -1 ). Finally, we investigate the origin of the extended Ly α emission but we conclude that our data do not allow us to disentangle the possible processes, i.e. scattering from star-forming regions, fluorescence, cooling radiation from cold gas accretion, and emission from satellite galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/69e4360d2ac7ec00f130a4454ff1663c58cd916a

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Citations in the corpus

The MUSE Hubble Ultra Deep Field Survey: I. Survey description, data reduction and source detection (2017, background): “Extended Lyα haloes around individual Lyα emitters are discussed in Paper VIII (Leclercq et al. 2017).”
Inferences on the timeline of reionization at z ∼ 8 from the KMOS Lens-Amplified Spectroscopic Survey (2019, background): “…and kinematics of galaxies out to z ∼ 2 (Förster Schreiber et al. 2009; Epinat et al. 2009; Wisnioski et al. 2015; Stott et al. 2016; Genzel et al. 2017) and revealed diffuse Lyα halos around z∼< 6 galaxies (Bacon et al. 2014; Karman et al. 2016; Wisotzki et al. 2016; Leclercq et al. 2017).”