FLARE is a space mission whose primary goal (~70% of its lifetime) will be to identify and study the universe before the end of the reionization at z > 6, detect, identify and study "first light" galaxies at dawn of time. A secondary objective (~20% of lifetime) is to survey star formation in the Milky Way. The remaining 10% will be dedicated to pointed observations, e.g., targets of opportunity and open time guest proposals. FLARE's strategy optimizes the science return: imaging and spectroscopic integral-field observations will be carried out simultaneously on two parallel focal planes and over very large instantaneous fields of view. The two above objectives have been better defined in several workshops held in Paris and in Marseille (details of the Marseille meeting in March 2016 are available at http://mission.lam.fr/flare/AgendaMar2016.html).
A comparison of FLARE's surveys with the COSMOS survey overlaid on a millenium simulation.
The objectives and legacy of FLARE can be summarized in two major questions that are related to two of ESA Cosmic Vision themes:
A. "How did the universe originate and what is it made of? "
To address this question, FLARE strategy will be make use of three methods to make the best and most complete census so far of the objects that dwell in the early universe before the end of reionization:
Projects like Euclid and W-FIRST do not have the relevant wavelength range to detect galaxies in rest-frame UV, i.e. 150nm. The following figures focus on a comparison between FLARE (200deg2, mAB=28.0) and JWST's surveys. For JWST, we assume Mason et al.'s (2015) surveys: Wide-Field (WF, 1deg2, mAB=29.3), Medium Deep (MD, 0.1deg2, mAB=30.6) and Ultra Deep (UD, mAB=32.0). The following figureq give some information on the number of detected objects and the volumes covered by several projects to detect galaxies in UV.
Number of galaxies at z = 10
Number of galaxies at z = 14
Number of galaxies as a function of the redshift (mean of several models for FLARE (200deg2, mAB=28.0) and JWST's surveys. For JWST, we assume Mason et al.'s (2015) surveys: Wide-Field (WF, 1deg2, mAB=29.3), Medium Deep (MD, 0.1deg2, mAB=30.6) and Ultra Deep (UD, mAB=32.0)
i. When and How Did Galaxies Form? Photometric identification of star-forming primordial galaxies at 10 < z < 15, i.e. less than 0.3 - 0.5 Gyr after the Big Bang. These will be selected through the Lyman break technique: intervening neutral hydrogen will absorb all light at wavelengths short-ward of Lyman-alpha 1216. in the rest-frame, causing the highest-redshift objects to "drop out" of visible and near-infrared images. The expected density of these galaxies at z > 14 is estimated to be about 1 deg-2 at mAB = 28, so in order to detect about 100 sources at the highest redshifts, we therefore need to cover at least 100 deg2. We need of the order of a hundred sources so as to determine the luminosity function and its evolution with redshift (particularly the shape at the bright end, which will probe the effects of feedback at early times). This sample of luminous galaxies will, very likely, be the largest one obtained with any facility for two reasons: (1) JWST is highly unlikely to build surveys much larger than about 1 deg2, i.e., HST-like. This means that the probability of detecting such luminous galaxies is low at z > 12 and (2) detecting these primordial galaxies requires any facility to have at least 2 bands at lambda > 1.3um (for z = 10) and lambda > 2.0um (for z = 15), in order to provide robust colours at wavelengths beyond the Lyman break for photometric redshifts. To date, only JWST and FLARE have a wavelength range extending beyond lambda = 2.0um with the required sensitivity. This topic will mainly use the imaging survey, which is the only one to cover an area > 200 deg2 deg2.
ii. Spectroscopic detection and identification of photometrically faint emission line galaxies via a blind spectroscopic survey : Imaging surveys allow us to detect galaxies with a strong continuum. However, we know that an important subset of galaxies, younger and undergoing strong star-bursting events, are optimally detected via spectroscopic surveys aiming at strong emission lines. VLT MUSE preliminary results (Bacon et al. 2015) discovered 26 Ly alpha emitting galaxies that are completely undetected in the HST WFPC2 deep broad-band images down to I814 > 29.5 magnitudes (AB). These sources that have no HST counterparts represent 30% of the entire Ly alpha emitter sample. A blind and relatively wide-field integral-field spectroscopic (IFS) survey is the unique way to detect these objects – this approach provides a great sensitivity advantage over "slitless" spectroscopy, even from space, where each pixel records background noise at all wavelengths. No other current or planned facility will feature an IFS instrument with such a large field-of-view. FLARE integral-field spectrograph will build a survey via parallel observations and reach magnitudes as deep as the widest JWST NIRSpec survey but over a much larger area of 1.5 deg2 (ten times that anticipated for the NIRSpec survey to the same limiting flux). Moreover, JWST/NIRSpec will not obtain spectroscopy over its entire field of view since a prior photometric detection is needed to define the slits for the micro-shutter arrays (and the alternative Integral Field Spectroscopic mode on NIRSpec only covers 3x3arcsec2, only 0.03% of the full field of the NIRSpec micro-shutter array). Integral field spectroscopy with FLARE will look for signatures of the first generation of Population III stars in the earliest galaxies, as well as charting the evolution of metal enrichment and the assembly of mass in galaxies over cosmic time and will determine the escape fraction of ionizing photons from high redshift galaxies (a key unanswered question in understanding the role of galaxies in the reionization of the intergalactic medium).
The detection of [OIII]5007 by FLARE and JWST NIRSpec Medium and Shallow surveys at z = 6 to z = 9.
iii. The first quasars and massive black holes : The density of very high redshift (z>6) luminous quasars is very low, with only one currently know at z>7, although the very existence of supermassive black holes at these early times presents strong challenges to seed formation and black-hole growth models. FLARE field-of-view is large enough to directly detect 10-30 quasars at z > 7 (depending on the evolution), and we will explore down to fainter luminosities than current surveys. Moreover, we will provide sufficient time in FLARE observation schedule to observe photometrically and spectroscopically these quasars. They will provide a unique information of the early co-evolution of galaxies and super-massive black holes but also, they will allow to study the intergalactic medium on the line of sight. The IFS will be very valuable to try and detect the environment of these early super-massive black holes.
The following figure gives some information on the volumes covered by several projects to detect galaxies in UV down to a given Star Formation Rate. We also show the FLARE 5000 deg2 survey that is designed to study the MW but might provide interesting targets, especially bright QSOs.
B) "What are the conditions for planet formation and the emergence of life?" and more specifically, "From gas and dust to stars and planets"
i. How stars and their planetary systems form? Herschel and Spitzer allowed us to peer into star formation regions and study the interstellar medium in the Milky Way. High angular resolution is very important to analyse the local physics of star formation. But, the dust attenuation in these regions is very high because the young (proto-) stars are still embedded in their molecular, dusty birth cloud. Both high angular resolution and wavelength range beyond 2um are needed to "see" deep inside the clouds. Once again, JWST can provide this, but JWST field of view is much too small to cover large areas in the Milky Way. FLARE can achieve this.
FLARE will place the ESA community in a leading position to statistically study the early universe after JWST deep pin-hole surveys via an unbiased census of the objects residing in the early universe. The instrumental development of wide-field imaging and wide-field integral-field spectroscopy in space is the major breakthrough, and FLARE will provide revolutionary gains by covering the crucial longer wavelengths inaccessible from ground-based observatories that are required to detect and characterize galaxies at z > 10.
Although galaxies beyond reionisation and the very early universe form the core (70 - 80% over 5 years) of the science objectives, FLARE's specifications and observations will be excessively useful for other topics and about 20% of FLARE's mission will be to observe regions in the Milky Way to build a survey of our galaxy and study in the IR (where the effect of dust are lower) its regions of stellar formation.
Several meetings related to WISH (FLARE's ancestor) and therefore to FLARE have been held in Japan and in France. The latest meeting being held in September 2014 in Marseille with a strong interest from the European community.
The first FLARE (First Light And Reionization Explorer) Meeting has been held in the Laboratoire d'Astrophysique de Marseille from March 14 at 10am to March 16 at 1pm. We had 1.5 days to discuss about FLARE's science and 1.0 days for the instrumentation.
A small and simple Python 3 code and illustrations are available here to estimate the sensitivities.
Last update: 18 March 2016 by Denis Burgarella