Query : 2018A&A...619A.136M

2018A&A...619A.136M - Astronomy and Astrophysics, volume 619A, 136-136 (2018/11-1)

Confirmation of double peaked Lyα emission at z=6.593. Witnessing a galaxy directly contributing to the reionisation of the Universe.


Abstract (from CDS):

Distant luminous Lyman-α emitters (LAEs) are excellent targets for spectroscopic observations of galaxies in the epoch of reionisation (EoR). We present deep high-resolution (R=5000) VLT/X-shooter observations, along with an extensive collection of photometric data of COLA1, a proposed double peaked LAE at z=6.6. We rule out the possibility that COLA1's emission line is an [OII] doublet at z=1.475 on the basis of i) the asymmetric red line-profile and flux ratio of the peaks (blue/red=0.31±0.03) and ii) an unphysical [OII]/Hα ratio ([OII]/Hα>22). We show that COLA1's observed B-band flux is explained by a faint extended foreground LAE, for which we detect Lyα and [OIII] at z=2.142. We thus conclude that COLA1 is a real double-peaked LAE at z=6.593, the first discovered at z>6. COLA1 is UV luminous (M1500=-21.6±0.3), has a high equivalent width (EW0,Lyα=120–40+50Å and very compact Lyα emission (r50,Lyα=0.33–0.04+0.07kpc). Relatively weak inferred Hβ+[OIII] line-emission from Spitzer/IRAC indicates an extremely low metallicity of Z<1/20Z or reduced strength of nebular lines due to high escape of ionising photons. The small Lyα peak separation of 220±20km/s implies a low HI column density and an ionising photon escape fraction of ~=15-30%, providing the first direct evidence that such galaxies contribute actively to the reionisation of the Universe at z>6. Based on simple estimates, we find that COLA1 could have provided just enough photons to reionise its own ~=0.3pMpc (2.3cMpc) bubble, allowing the blue Lyα line to be observed. However, we also discuss alternative scenarios explaining the detected double peaked nature of COLA1. Our results show that future high-resolution observations of statistical samples of double peaked LAEs at z>5 are a promising probe of the occurrence of ionised regions around galaxies in the EoR.

Abstract Copyright: © ESO 2018

Journal keyword(s): galaxies: high-redshift - galaxies: formation - dark ages - reionization - first stars - techniques: spectroscopic - intergalactic medium

VizieR on-line data: <Available at CDS (J/A+A/619/A136): spectrum.dat xshoot_cola1.fits>

Simbad objects: 7

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Number of rows : 7
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 NAME Himiko EmG 02 17 57.6122 -05 08 44.898           ~ 101 0
2 GD 71 WD* 05 52 27.6198591816 +15 53 13.228887444 11.675 12.783 13.032 13.169 13.337 DA1.5 383 0
3 CALYMHA -S16-147 EmG 10 00 13.909 +01 39 24.30           ~ 4 0
4 NAME COSMOS Field reg 10 00 28.60 +02 12 21.0           ~ 2867 0
5 HSCS J100058+014815 EmG 10 00 58.01148 +01 48 15.3000           ~ 86 0
6 HSCS J100124+023145 EmG 10 01 24.80 +02 31 45.4           ~ 16 0
7 NAME COLA1 EmG 10 02 35.380 +02 12 13.96           ~ 28 0

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