Early Results from GLASS-JWST. X. Rest-frame UV-optical Properties of Galaxies at 7 < z < 9

Abstract

We present the first James Webb Space Telescope/NIRCam-led determination of 7 &lt; z &lt; 9 galaxy properties based on broadband imaging from 0.8 to 5 μm as part of the GLASS-JWST Early Release Science program. This is the deepest data set acquired at these wavelengths to date, with an angular resolution ≲0.″14. We robustly identify 13 galaxies with signal-to-noise ratio ≳ 8 in F444W from 8 arcmin2 of data at m AB ≤ 28 from a combination of dropout and photometric redshift selection. From simulated data modeling, we estimate the dropout sample purity to be ≳90%. We find that the number density of these F444W-selected sources is broadly consistent with expectations from the UV luminosity function determined from Hubble Space Telescope data. We characterize galaxy physical properties using a Bayesian spectral energy distribution fitting method, finding a median stellar mass of 108.5 M ⊙ and age 140 Myr, indicating they started ionizing their surroundings at redshift z &gt; 9.5. Their star formation main sequence is consistent with predictions from simulations. Lastly, we introduce an analytical framework to constrain main-sequence evolution at z &gt; 7 based on galaxy ages and basic assumptions, through which we find results consistent with expectations from cosmological simulations. While this work only gives a glimpse of the properties of typical galaxies that are thought to drive the reionization of the universe, it clearly shows the potential of JWST to unveil unprecedented details of galaxy formation in the first billion years.

Early Results from GLASS-JWST. XIV. A Spectroscopically Confirmed Protocluster 650 Million Years after the Big Bang

“…Among those, YD4 is the most significant case with A V = 1.1, which is consistent with the ∼4σ detection in dust continuum at its position (Laporte et al 2017; see also Section 4.4). We compare A V values for our sample to those of a reference field sample that consists of 13 photometric sources at z ∼ 8 from Leethochawalit et al (2023). While the distribution of our sample is skewed toward higher A V , the shift is not statistically significant.…”

Early Results from GLASS-JWST. XIX. A High Density of Bright Galaxies at z ≈ 10 in the A2744 Region

“…For all selected candidates we estimate photometric redshifts with EAZY (Brammer et al 2008) and ZPHOT (Fontana et al 2000). The EAZY code was run assuming a flat prior with two different sets of templates: the default V1.3 spectral template (see Leethochawalit et al 2023) and the recently released templates by Larson et al (2022) specifically designed for the analysis of JWST-selected galaxies at very high redshift. The analysis with ZPHOT has been performed as described by Santini et al (2023) by fitting the observed photometry with Bruzual & Charlot (2003, BC03 hereafter) templates having both declining and delayed star formation histories; it models the contribution from nebular continuum and line emission following Schaerer & de Barros (2009) and Castellano et al (2014).…”

Early Results from GLASS-JWST. XI. Stellar Masses and Mass-to-light Ratio of z > 7 Galaxies

“…When the nominal flux errors are smaller than 0.05 mag, we set a minimum photometric uncertainty in all bands corresponding to this threshold to account for uncertainties in the NIRCam calibration. We adopt in the following the photometric redshifts computed by Leethochawalit et al (2022) and Castellano et al (2022). We fixed the redshift to the EAZY z peak value, with the exception of two of the z > 9 color-selected galaxies (GHZ3 and GHZ5 in Castellano et al 2022), for which EAZY prefers a lower-redshift solution while ZPHOT fits them at z > 9.…”