Astrophys. J., 818, 38 (2016/February-2)
The Grism Lens-Amplified Survey from Space (GLASS). III. A census of Lyα emission at z ≳ 7 from HST spectroscopy.
SCHMIDT K.B., TREU T., BRADAC M., VULCANI B., HUANG K.-H., HOAG A., MASEDA M., GUAITA L., PENTERICCI L., BRAMMER G.B., DIJKSTRA M., DRESSLER A., FONTANA A., HENRY A.L., JONES T.A., MASON C., TRENTI M. and WANG X.
Abstract (from CDS):
We present a census of Lyα emission at z ≳ 7, utilizing deep near-infrared Hubble Space Telescope grism spectroscopy from the first six completed clusters of the Grism Lens-Amplified Survey from Space (GLASS). In 24/159 photometrically selected galaxies we detect emission lines consistent with Lyα in the GLASS spectra. Based on the distribution of signal-to-noise ratios and on simulations, we expect the completeness and the purity of the sample to be 40%-100% and 60%-90%, respectively. For the objects without detected emission lines we show that the observed (not corrected for lensing magnification) 1σ flux limits reach 5x10–18 erg/s/cm2 per position angle over the full wavelength range of GLASS (0.8-1.7 µm). Based on the conditional probability of Lyα emission measured from the ground at z ∼ 7, we would have expected 12-18 Lyα emitters. This is consistent with the number of detections, within the uncertainties, confirming the drop in Lyα emission with respect to z ∼ 6. Deeper follow-up spectroscopy, here exemplified by Keck spectroscopy, is necessary to improve our estimates of completeness and purity and to confirm individual candidates as true Lyα emitters. These candidates include a promising source at z = 8.1. The spatial extent of Lyα in a deep stack of the most convincing Lyα emitters with <z> = 7.2 is consistent with that of the rest-frame UV continuum. Extended Lyα emission, if present, has a surface brightness below our detection limit, consistent with the properties of lower-redshift comparison samples. From the stack we estimate upper limits on rest-frame UV emission line ratios and find fCIV/f_Ly α ≲ 0.32 and fCIII/fLyα ≲ 0.23, in good agreement with other values published in the literature.
galaxies: high-redshift - methods: data analysis - techniques: spectroscopic
Tables 2-3+5-6: [STB2016] GLASS A2744 NNNNN N=38 among (Nos 00085-02428), [STB2016] GLASS MACS0717 NNNNN N=4 among (Nos 00370-02068), [STB2016] GLASS MACS1423 NNNNN N=10 (Nos 00435-01619), [STB2016] GLASS MACS2129 NNNNN N=6 among (Nos 00677-01792), [STB2016] GLASS RXJ1347 NNNNN N=13 among (Nos 00091-01745), [STB2016] GLASS RXJ2248 NNNNN N=8 among (Nos 00207-01953).
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