Signature of the first galaxies in JWST deep field observations

Abstract

We examine the assembly process and the observability of a first galaxy (M vir ≈ 10 9 M at z ≈ 8) with cosmological zoom-in, hydrodynamic simulations, including the radiative, mechanical, and chemical feedback exerted by the first generations of stars. To assess the detectability of such dwarf systems with the upcoming James Webb Space Telescope (JWST), we construct the spectral energy distribution for the simulated galaxy in a post-processing fashion. We find that while the non-ionizing UV continuum emitted by the simulated galaxy is expected to be below the JWST detection limit, the galaxy might be detectable using its nebular emission, specifically in the Hα recombination line. This requires that the galaxy experiences an active starburst with a star formation rate of M * 0.1 M yr −1 at z ≈ 9. Due to the bursty nature of star formation in the first galaxies, the time interval for strong nebular emission is short, less than 2 − 3 Myr. The probability of capturing such primordial dwarf galaxies during the observable part of their duty cycle is thus low, resulting in number densities of order one source in a single pointing with MIRI onboard the JWST, for very deep exposures. Gravitational lensing, however, will boost their observability beyond this conservative baseline. The first sources of light will thus come firmly within our reach.

Formation of the first galaxies in the aftermath of the first supernovae

“…7, the star formation in first galaxies takes place intermittently due to the stellar feedback. Correspondingly, the flux densities violently fluctuate in time, as also found by Jeon & Bromm (2019). The dotted lines in Fig.…”

“…We have adopted the stochastic thermal feedback model, which successfully produce galactic outflows by overcoming the over-cooling problem (e.g, Katz et al 1996). We observed a clumpy gas structure and intermittent star formation history in the first galaxies (see also Jeon & Bromm 2019). On the other hand, previous studies with different feedback models instead found a long-standing disk structure and continuous star formation (Pawlik et al 2011(Pawlik et al , 2013Ricotti et al 2016).…”

Deep into the structure of the first galaxies: SERRA views

“…This entails a lowerΣ for the patches of gas with similar Σg. Such low mean metallicity is not found for relatively massive (M > ∼ 10 8 M ) and star forming (SFR > ∼ 0.1M yr −1 ) galaxies; low mean ISM metallicities (Z < ∼ 0.05 Z ) are typical of smaller (M > ∼ 10 7 M ) systems with lower star formation (SFR < ∼ 0.1 M yr −1 Jeon et al 2015;Jeon & Bromm 2019); for these galaxies, metallicity can play a role as relevant as burstiness, however currently no ALMA [C II] detection is available for galaxies with SFR < ∼ 1 M yr −1 . The two resolved relations can be further analysed by extracting the PDFs of Σ [CII] -Σ andΣ -Σg.…”

Dwarf satellites of high-z Lyman Break Galaxies: a free lunch for JWST

“…The physical and observational properties of isolated dwarf galaxies located in the field have been widely studied through cosmological simulations (Wise et al 2014;Zackrisson et al 2017;Jeon & Bromm 2019). However, we also expect the presence of an additional category of dwarf galaxies: the satellites orbiting around more massive galaxies in the densest regions of the cosmic web (e.g Conroy et al 2006).…”