JWST will address key questions in determining how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present. JWST will also discern the role of active galactic nuclei such as quasars or other supermassive black holes on the process of reionization. Recent observations of the most distant quasars, combined with cosmic microwave background observations made by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite tell us that reionization ended about 1 billion years after the Big Bang. JWST will take spectra of still more distant quasars to establish whether reionization is brought about by the first-light objects, or subsequent generations, and follow the process of reionization through its conclusion. The time lag between first light and reionization is uncertain. As reionization progressed, the bubbles got bigger and began to join together, finally filling all of the space between the galaxies. Each galaxy began by creating a bubble of ionized gas around it. Reionization represents the last global phase transition the universe underwent after the Big Bang. These galaxies were bright in UV light, and began to dissociate the protons and electrons of the hydrogen atoms in a process called reionization. Bouwens (UCO/Lick Observatory and Leiden University), and the HUDF09 Team.įollowing their formation, the first galaxies began to grow by accreting gas and through mergers. Illingworth (UCO/Lick Observatory and the University of California, Santa Cruz), R. The WFC3 deep field obtained with the recently installed WFC3/IR camera on the Hubble Space Telescope. Follow-up spectroscopy and images in the mid-IR (MIR) will also teach us more about the objects that are seen in the NIRCam images. The tunable filter imager will employ narrow-band imaging surveys to search for H α emission from these galaxies. This approach has been especially successful in deep-field observations such as the Hubble deep field, 1 the Hubble ultra-deep field, 2 and, most recently, the Wide Field Camera 3 (WFC3) deep field, 3 as shown in Fig. 2. This will require ∼ 100 h exposures each, in several broadband filters using the near IR camera (NIRCam) instrument. By taking very long exposures in the NIR, JWST will be able to see the first stars exploding as supernovae, and the first galaxies as they form. In order to detect these faint sources, JWST requires a large collecting area, excellent image quality at 2 μm, the low backgrounds that come from observing above the atmosphere, and the cryogenic operating temperature of the observatory. The first galaxies formed with about a million solar masses of stars radiating strongly in the rest-frame ultraviolet (UV) and visible, which is red shifted into the near IR (NIR). The first sources of light acted as seeds for the successive formation of larger objects, and by studying these objects we will learn the processes that formed the nuclei of present day giant galaxies. The current leading models for structure formation predict a hierarchical assembly of galaxies and clusters. Understanding these first sources is critical, since they significantly influenced subsequent structures. The emergence of the first sources of light in the universe marks the end of the “Dark Ages” in cosmic history, a period characterized by the absence of discrete sources of light. One of the primary motivations for JWST is to identify the first luminous sources to form, and determine the ionization history of the universe (see Fig. 1). First Light and Reionization (The End of the Dark Ages) An overview is presented of the architecture and selected optical design features of JWST are described.ġ.1. A suite of instruments will provide the capability to observe over a spectral range from 0.6- to 27-μm wavelengths with imaging and spectroscopic configurations. Routine wavefront sensing and control measurements are used to achieve phasing of the segmented primary mirror and initial alignment of the telescope. The large size of the telescope and spacecraft systems require that they are stowed for launch in a configuration that fits the Ariane 5 fairing, and then deployed after launch. Passive cooling is facilitated by means of a large sunshield that provides thermal isolation and protection from direct illumination from the Sun. It will operate at cryogenic temperature (40 K), achieved via passive cooling, in an orbit about the Earth-Sun second Lagrange point (L2). JWST is a segmented architecture telescope with an aperture of 6.6 m. ![]() ![]() The James Webb Space Telescope (JWST) is an infrared space telescope designed to explore four major science themes: first light and reionization, the assembly of galaxies, the birth of stars and protoplanetary systems, and planetary systems and origins of life.
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