Early Results from GLASS-JWST. I: Confirmation of Lensed z ≥ 7 Lyman-break Galaxies behind the Abell 2744 Cluster with NIRISS

October 2022 • 2022ApJ...938L..13R

Authors • Roberts-Borsani, Guido • Morishita, Takahiro • Treu, Tommaso • Brammer, Gabriel • Strait, Victoria • Wang, Xin • Bradac, Marusa • Acebron, Ana • Bergamini, Pietro • Boyett, Kristan • Calabró, Antonello • Castellano, Marco • Fontana, Adriano • Glazebrook, Karl • Grillo, Claudio • Henry, Alaina • Jones, Tucker • Malkan, Matthew • Marchesini, Danilo • Mascia, Sara • Mason, Charlotte • Mercurio, Amata • Merlin, Emiliano • Nanayakkara, Themiya • Pentericci, Laura • Rosati, Piero • Santini, Paola • Scarlata, Claudia • Trenti, Michele • Vanzella, Eros • Vulcani, Benedetta • Willott, Chris

Abstract • We present the first search for z ≥ 7, continuum-confirmed Lyman break sources with NIRISS/WFS spectroscopy over the Abell 2744 Frontier Fields cluster, as part of the GLASS-JWST-ERS survey. With ~15 hr of preimaging and multiangle grism exposures in the F115W, F150W, and F200W filters, we describe the general data handling (i.e., reduction, cleaning, modeling, and extraction processes) and analysis for the GLASS-JWST survey. We showcase the power of JWST to peer deep into reionization, when most intergalactic hydrogen is neutral, by confirming two galaxies at z = 8.04 ± 0.15 and z = 7.90 ± 0.13 by means of their Lyman breaks. Fainter continuum spectra are observed in both the F150W and F200W bands, indicative of blue (-1.69 and -1.33) UV slopes and moderately bright absolute magnitudes (-20.37 and -19.68 mag). We do not detect strong Lyα in either galaxy, but do observe tentative (~2.7-3.8σ) He II λ1640 Å, O III]λλ1661,1666 Å, and N III]λλ1747,1749 Å line emission in one, suggestive of low-metallicity, star-forming systems with possible nonthermal contributions. These novel observations provide a first look at the extraordinary potential of JWST/NIRISS for confirming representative samples of bright z ≥ 7 sources in the absence of strong emission lines, and gain unprecedented insight into their contributions toward cosmic reionization.


IPAC Authors


Takahiro Morishita

Assistant Scientist