A First Transients Survey with JWST: the FLARE project

Abstract

The James Webb Space Telescope (JWST) was conceived and built to answer one of the most fundamental questions that humans can address empirically: "How did the Universe make its first stars?". This can be attempted in classical stare mode and by still photography -with all the pitfalls of crowding and multiband redshifts of objects of which a spectrum was never obtained. Our First Lights At REionization (FLARE) project transforms the quest for the epoch of reionization from the static to the time domain. It targets the complementary question: "What happened to those first stars?". It will be answered by observations of the most luminous events: supernovae and accretion on to black holes formed by direct collapse from the primordial gas clouds. These transients provide direct constraints on star-formation rates and the truly initial initial mass function, and they may identify possible stellar seeds of supermassive black holes. Furthermore, our knowledge of the physics of these events at ultra-low metallicity will be much expanded. JWST's unique capabilities will detect these most luminous and earliest cosmic messengers easily in fairly shallow observations. However, these events are very rare at the dawn of cosmic structure formation and so require large area coverage. Time domain astronomy can be advanced to an unprecedented depth by means of a shallow field of JWST reaching 27 mag (AB) in 2 µm and 4.4 µm over a field as large as 0.1 square degree visited multiple times each year. Such a survey may set strong constraints or detect massive Population III supernovae at redshifts beyond 10, pinpointing the redshift of the first stars, or at least their death. Based on our current knowledge of superluminous supernovae, such a survey will find one or more superluminous supernovae at redshifts above 6 in five years and possibly several direct collapse black holes.In addition, the large scale structure that is the trademark of the epoch of reion--3ization will be detected. Although JWST is not designed as a wide field survey telescope, we show that such a wide field survey is possible with JWST and is critical in addressing several of its key scientific goals.

ASTRO2020 White Paper: JWST: Probing the Epoch of Reionization with a Wide Field Time-Domain Survey

“…Natarajan et al (2017) predicted the observational properties and JWST detectability of black hole seeds, formed by the direct collapse of high-redshift halos (e.g., Bromm & Loeb, 2003), or as remnants of Pop III stars (e.g., Volonteri et al, 2003). These black holes are bright enough that JWST can easily observe them up to z beyond 10 ( Wang et al, 2017). Their comparatively lower mass also makes them more prone to short term variability than SMBHs.…”

“…Pop III supernovae: A primary goal of a JESS may be Pop III supernovae. High-redshift SNe can directly probe the first generations of stars and their formation rates because they can be observed at great distances and, to some degree, the mass of the progenitor can be inferred from the light curve of the explosion (Tanaka et al, 2013;de Souza et al, 2013de Souza et al, , 2014Wang et al, 2017). At ∼ 100 M ⊙ non-rotating Pop III stars can encounter the pair instability (Heger et al, 2003).…”

“…No ground-based facilties are capable of discovering them at z beyond 6. They are expected to be very rare and only a deep survey down to 27th mag in the IR with JWST, with a field of view of about 1 square degree, can such supernovae be discovered (Wang et al, 2017;Regos & Vinko, 2018).…”

“…The thermonuclear SNe are from a population of progenitors with well constrained ages and metallicity and can thus provide critical information on the physics related to the thermonuclear explosion. More details can be found in Wang et al (2017).…”

When did Population III star formation end?

“…zPopIII ∼ 5, it cannot afford a large survey area. For instance, the FoV considered by the First Lights at REionization (FLARE) project is only ∼ 0.1 deg 2 , such that detection of Pop III PISNe is unlikely to be achieved in a survey time of a few years (Wang et al 2017;Regős et al 2020). In our calculation of the PISN rates, we assume a Pop III PISN efficiency PISN = 10 −3 M −1 for typical top-heavy Pop III IMFs.…”