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THE JAMES WEBB SPACE TELESCOPE

A REVOLUTIONARY OBSERVATORY TO STUDY THE DISTANT UNIVERSE

The James Webb Space Telescope (JWST) is NASA/ESA's flagship observatory, considered the successor to the Hubble Space Telescope and launched on 25th December, 2021. The primary goals of JWST will be to observe and characterise distant galaxies and the atmospheres of exoplanets. Unlike Hubble, JWST will primarily observe in the infrared, where distant galaxies emit the majority of their starlight, and thus will push the frontier of observational cosmology and the search for galaxies close to the beginning of time. For a nice review, have a read of this Nature summary.

JWST will be armed with four primary instruments (NIRCam, NIRISS, NIRSpec and MIRI), each with their own imaging and/or spectroscopic capabilities. Each of these instruments are well-suited to particular tasks: NIRCam will provide imaging in a wide variety of infrared filters, needed to discover new galaxies in blank patches of the sky, NIRISS will provide ~1 micron slitless spectroscopy over each of the camera's pointings, allowing for redshift (or distance) determinations of both previously unknown and known sources, NIRSpec will provide both low- and high-resolution spectroscopy over the entire rest-frame optical spectrum of distant galaxies allowing for unprecedented characterisation of their properties, and MIRI will provide both imaging and spectroscopy at >5 microns allowing for characterisation over even longer wavelengths.

My work on JWST focuses on simulating and analysing realistic data sets from upcoming programs. Of these, I am leading efforts for two (ERS 1324, PI Treu and GO 1747, PI Roberts-Borsani) and am a core member of an additional three. I provide a brief description of each below.

ERS-1324: Through the Looking GLASS (GLASS-JWST)
PI: Tommaso Treu

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Through the Looking GLASS (GLASS-JWST), is a James Webb Space Telescope (JWST) Early Release Science (ERS) program led by Prof. Tommaso Treu at the University of California, Los Angeles (UCLA). The two main science theses of GLASS-JWST are to (i) understand the Reionization process of the universe less than 1 billion years after the Big Bang, and (ii) understand how gas and heavy elements are distributed within and around galaxies over cosmic time. For a full description, see the survey paper here.

GLASS-JWST achieves this by combining the natural magnifying power of gravitationally lensing by the massive Frontier Field galaxy cluster, Abell 2744, with JWST's unprecedented instruments (NIRISS, NIRCam and NIRSpec) to measure detailed properties of distant galaxies in the early universe.

GLASS-JWST observes the Abell 2744 cluster in two modes. The first (completed as of June 29, 2022) is over the central portion of the cluster with NIRISS Wide-Field Slitless Spectroscopy (WFSS) in three different filters (F115W, F150W, F200W) in order to obtain continuous, R~150 spectra over the entire ~1.1-2.2 micron wavelength range. Simultaneously, JWST obtained imaging over parallel fields in seven different wide-band filters (F090W, F115W, F150W, F200W, F277W, F356W, F444W). The second mode will consist of NIRSpec Multi-Object Spectroscopy (MOS) for a sample of sources identified in the primary NIRISS field, with three different setups (G140H/F100LP, G235H/F170LP, and G395H/F290LP) affording complementary high-resolution (R~2700) spectra. As with the NIRISS, the NIRSpec observations will also be conducted with NIRCam parallel imaging using the same filters.

Within only the first couple of weeks, GLASS team members used the first data to make unprecedented discoveries that have garnered international attention and been published in high-profile journals. Some of these include (but are not limited to) the discovery of early galaxy candidates only ~400 Myrs after the Big Bang with NIRCam, the spectral confirmation of two of the most distant galaxies to date with NIRISS spectroscopy, the characterization of inverted metallicity gradients in local galaxies with NIRISSthe identification of a distant supernova with NIRISS, and the characterization of a distant, lensed star.

GO-1747: Linking Bright Galaxy Properties to IGM Opacity and Environment in the Early Epoch of Reionization with NIRSpec
PI: Roberts-Borsani

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This ambitious program aims to follow up 10 luminous and ultra-distant galaxy candidates with the NIRSpec instrument, each identified as part of the Brightest of Reionizing Galaxies (BoRG) survey with the Hubble Space Telescope. The sample of galaxies represent some of the most typical and distant objects currently known, thought to have formed only a few hundred million years after the Big Bang. The observations carried out here will enable for the first time (through prism spectroscopy), the characterization of the ages, masses, and metallicities of the underlying young UV-bright stars and older stellar populations, as well as determining the impact on their immediate surroundings and the Universe as a whole. A unique aspect of this program is that it will be able to map all rest-frame UV and rest-frame optical emission lines, thus characterizing which heavy elements (e.g., Carbon, Oxygen, Nitrogen) are present in each of the galaxies, allowing us to place constraints on whether such objects already have supermassive black holes, evolved stars and supernovae, and extreme stars. First observations are scheduled for February 2023.