Guido Roberts-Borsani

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 in an additional three. I provide the official abstracts of each of these programs here below, for reference.

The Abell 2744 Frontier Fields cluster, whose massive gravitational pull magnifies the light of distant galaxies behind it.

ERS 1324: Through the Looking GLASS
(PI Tommaso Treu)
GLASS is focused on two main science areas: understanding the Reionization of the universe less than 1 billion years after the Big Bang, and understanding how gas and heavy elements are distributed within and around galaxies over time. The program will combine the natural magnifying power of gravitational lensing by studying the massive Frontier Fields galaxy cluster, Abell 2744, with JWST's incredible sensitivity to measure detailed properties of distant galaxies in the early universe.

The program will build on GLASS' extensive Hubble Space Telescope analysis, which used grism spectroscopy to obtain slitless spectra over the entire cluster area, by observing the cluster area with JWST NIRISS wide-field slitless spectroscopy (WFSS) mode and targeted NIRSpec follow-up spectroscopy of known sources, including some of the most distant galaxies currently known. Observations with the two instruments will enable GLASS to determine the distances and UV properties of previously known and unknown galaxies, as well as more detailed characterization of known galaxies. Additionally, the program will simultaneously take images of blank patches of the sky with the NIRCam instrument, thereby revealing new galaxies candidates.

One of the BoRG candidates identified for JWST/NIRSpec follow up. This image is a 6.5'x6.5' cutout of a Hubble image taken with the WFC3 camera.

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