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Title: Rest-frame UV Colors for Faint Galaxies at z ∼ 9–16 with the JWST NGDEEP Survey

We present measurements of the rest-frame UV spectral slope,β, for a sample of 36 faint star-forming galaxies atz∼ 9–16 discovered in one of the deepest JWST NIRCam surveys to date, the Next Generation Deep Extragalactic Exploratory Public Survey. We use robust photometric measurements for UV-faint galaxies (down toMUV∼ −16), originally published in Leung et al., and measure values of the UV spectral slope via photometric power-law fitting to both the observed photometry and stellar population models obtained through spectral energy distribution (SED) fitting withBagpipes. We obtain a median and 68% confidence interval forβfrom photometric power-law fitting ofβPL=2.70.5+0.5and from SED fitting,βSED=2.30.1+0.2for the full sample. We show that when only two to three photometric detections are available, SED fitting has a lower scatter and reduced biases than photometric power-law fitting. We quantify this bias and find that after correction the medianβSED,corr=2.50.2+0.2. We measure physical properties for our galaxies withBagpipesand find that our faint (MUV=18.10.9+0.7) sample is low in mass (log[M*/M]=7.70.5+0.5), fairly dust-poor (Av=0.10.1+0.2mag), and modestly young (log[age]=7.80.8+0.2yr) with a median star formation rate oflog(SFR)=0.30.4+0.4Myr1. We find no strong evidence for ultrablue UV spectral slopes (β∼ −3) within our sample, as would be expected for exotically metal-poor (Z/Z< 10−3) stellar populations with very high Lyman continuum escape fractions. Our observations are consistent with model predictions that galaxies of these stellar masses atz∼ 9–16 should have only modestly low metallicities (Z/Z∼ 0.1–0.2).

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Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal Letters
Medium: X Size: Article No. L24
["Article No. L24"]
Sponsoring Org:
National Science Foundation
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