Evidence for Pop III-like stellar populations in the most luminous Lyman-α emitters at the epoch of re-ionisation:spectroscopic confirmation

Sobral, David and Matthee, Jorryt and Darvish, Behnam and Schaerer, Daniel and Mobasher, Bahram and Röttgering, Huub J. A. and Da Graça Santos, Sergio and Hemmati, Shoubaneh (2015) Evidence for Pop III-like stellar populations in the most luminous Lyman-α emitters at the epoch of re-ionisation:spectroscopic confirmation. The Astrophysical Journal, 808 (2). ISSN 0004-637X

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Abstract

Faint Lyman-$\alpha$ (Ly$\alpha$) emitters become increasingly rarer towards the re-ionisation epoch (z~6-7). However, observations from a very large (~5deg$^2$) Ly$\alpha$ survey at z=6.6 (Matthee et al. 2015) show that this is not the case for the most luminous emitters. Here we present follow-up observations of the two most luminous z~6.6 Ly$\alpha$ candidates in the COSMOS field: `MASOSA' and `CR7'. We used X-SHOOTER, SINFONI and FORS2 (VLT), and DEIMOS (Keck), to confirm both candidates beyond any doubt. We find redshifts of z=6.541 and z=6.604 for MASOSA and CR7, respectively. MASOSA has a strong detection in Ly$\alpha$ with a line width of $386\pm30$ km/s (FWHM) and with high EW$_0$ (>200 \AA), but it is undetected in the continuum. CR7, with an observed Ly$\alpha$ luminosity of $10^{43.93\pm0.05}$erg/s is the most luminous Ly$\alpha$ emitter ever found at z>6. CR7 reveals a narrow Ly$\alpha$ line with $266\pm15$ km/s FWHM, being detected in the NIR (rest-frame UV, with $\beta=-2.3\pm0.1$) with an excess in $J$, and also strongly detected in IRAC/Spitzer. We detect a narrow HeII1640$\AA$ emission line ($6\sigma$) which explains the excess seen in the $J$ band photometry (EW$_0$~80 \AA). We find no other emission lines from the UV to the NIR in our X-SHOOTER spectra, nor any signatures of Wolf-Rayet (WR) stars. We find that CR7 is best explained by a combination of a PopIII-like population which dominates the rest-frame UV and the nebular emission, and a more normal stellar population which dominates the mass. HST/WFC3 observations show that the light is indeed spatially separated between a very blue component, coincident with Ly$\alpha$ and HeII emission, and two red components (~5 kpc away), which dominate the mass. Our findings are consistent with theoretical predictions of a PopIII wave, with PopIII star formation migrating away from the original sites of star formation.

Item Type:
Journal Article
Journal or Publication Title:
The Astrophysical Journal
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/1900/1912
Subjects:
ID Code:
77525
Deposited By:
Deposited On:
06 Jan 2016 14:08
Refereed?:
Yes
Published?:
Published
Last Modified:
20 Oct 2020 03:48