James Webb Space Telescope Feed Post

Harvard ADS: All the Little Things in Abell 2744: >1000 Gravitationally Lensed Dwarf Galaxies at z=0-9 from JWST NIRCam Grism Spectroscopy

Paper abstract: Dwarf galaxies hold the key to crucial frontiers of astrophysics, however, their faintness renders spectroscopy challenging. Here we present the JWST Cycle 2 survey, All the Little Things (ALT, PID 3516), which is designed to seek late-forming Pop III stars and the drivers of reionization at z~6-7. ALT has acquired the deepest NIRCam grism spectroscopy yet (7-27 hr), at JWST's most sensitive wavelengths (3-4 \mum), covering the powerful lensing cluster Abell 2744. Over the same 30 arcmin^2, ALT's ultra-deep F070W+F090W imaging (~30 mag) enables selection of very faint sources at z>6. We demonstrate the success of ALT's novel ``butterfly" mosaic to solve spectral confusion and contamination, and introduce the ``Allegro" method for emission line identification. By collecting spectra for every source in the field of view, ALT has measured precise (R~1600) redshifts for 1630 sources at z=0.2-8.5. This includes one of the largest samples of distant dwarf galaxies: [1015, 475, 50] sources less massive than the SMC, Fornax, and Sculptor with \log(M_{*}/M_{\odot})<[8.5, 7.5, 6.5]. We showcase ALT's discovery space with: (i) spatially resolved spectra of lensed clumps in galaxies as faint as M_{\rm{UV}}~-15; (ii) large-scale clustering -- overdensities at z=[2.50, 2.58, 3.97, 4.30, 5.66, 5.77, 6.33] hosting massive galaxies with striking Balmer breaks; (iii) small-scale clustering -- a system of satellites around a Milky Way analog at z~6; (iv) spectroscopically confirmed multiple images that help constrain the lensing model underlying all science in this legacy field; (v) sensitive star-formation maps based on dust-insensitive tracers such as Pa\alpha; (vi) direct spectroscopic discovery of rare sources such as AGN with ionized outflows. These results provide a powerful proof of concept for how grism surveys maximize the potential of strong lensing fields.