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تسجيل مستخدم جديدTracing the reionization epoch with ALMA: [CII] emission in z~7 galaxies
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We present new results on [CII]158$mu$ m emission from four galaxies in the reionization epoch. These galaxies were previously confirmed to be at redshifts between 6.6 and 7.15 from the presence of the Ly$alpha$ emission line in their spectra. The Ly$alpha$ emission line is redshifted by 100-200 km/s compared to the systemic redshift given by the [CII] line. These velocity offsets are smaller than what is observed in z~3 Lyman break galaxies with similar UV luminosities and emission line properties. Smaller velocity shifts reduce the visibility of Ly$alpha$ and hence somewhat alleviate the need for a very neutral IGM at z~7 to explain the drop in the fraction of Ly$alpha$ emitters observed at this epoch. The galaxies show [CII] emission with L[CII]=0.6-1.6 x10$^8 L_odot$: these luminosities place them consistently below the SFR-L[CII] relation observed for low redshift star forming and metal poor galaxies and also below z =5.5 Lyman break galaxies with similar star formation rates. We argue that previous undetections of [CII] in z~7 galaxies with similar or smaller star formation rates are due to selection effects: previous targets were mostly strong Ly$alpha$ emitters and therefore probably metal poor systems, while our galaxies are more representative of the general high redshift star forming population .
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