7 research outputs found
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NGDEEP Epoch 1: the faint end of the luminosity function at z ∼ 9-12 from ultradeep JWST imaging
We present a robust sample of very high redshift galaxy candidates from the first epoch of JWST/NIRCam imaging from the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey. The NGDEEP NIRCam imaging, spanning 9.7 arcmin2 in the Hubble Ultra Deep Field Parallel Field 2, reaches m = 30.4 (5σ, point-source, 2″ diameter apertures corrected to total) in F277W, making it the deepest public JWST GO imaging data set to date. We describe our detailed data reduction process of the six-filter broadband JWST/NIRCam imaging, incorporating custom corrections for systematic effects to produce high-quality calibrated images. Using robust photometric redshift selection criteria, we identify a sample of 38 z ≳ 9 galaxy candidates. These objects span a redshift range of z = 8.5-15.8 and apparent magnitudes of m F277W = 27-30.5 AB mag, reaching ∼1.5 mag deeper than previous public JWST imaging surveys. We calculate the rest-frame ultraviolet luminosity function at z ∼ 9 and 11 and present a new measurement of the luminosity function faint-end slope at z ∼ 11. We find a faint-end slope of α = −2.5 ± 0.4 and −2.2 ± 0.2 at z ∼ 9 and 11, respectively. This is consistent with no significant evolution in the faint-end slope and number density from z = 9 to 11. Comparing our results with theoretical predictions, we find that some models produce better agreement at the faint end than the bright end. These results will help to constrain how stellar feedback impacts star formation at these early epochs.</p
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First look at <i>z</i> > 1 Bars in the rest-frame near-infrared with JWST early CEERS Imaging
Stellar bars are key drivers of secular evolution in galaxies and can be effectively studied using rest-frame near-infrared (NIR) images, which trace the underlying stellar mass and are less impacted by dust and star formation than rest-frame UV or optical images. We leverage the power of JWST CEERS NIRCam images to present the first quantitative identification and characterization of stellar bars at z > 1 based on rest-frame NIR F444W images of high resolution (∼1.3 kpc at z ∼ 1–3). We identify stellar bars in these images using quantitative criteria based on ellipse fits. For this pilot study, we present six examples of robustly identified bars at z > 1 with spectroscopic redshifts, including the two highest-redshift bars at z ∼ 2.136 and 2.312 quantitatively identified and characterized to date. The stellar bars at z ∼ 1.1–2.3 presented in our study have projected semimajor axes of ∼2.9–4.3 kpc and projected ellipticities of ∼0.41–0.53 in the rest-frame NIR. The barred host galaxies have stellar masses ∼1 × 1010 to 2 × 1011
M
⊙ and star formation rates of ∼21–295 M
⊙ yr−1, and several have potential nearby companions. Our finding of bars at z ∼ 1.1–2.3 demonstrates the early onset of such instabilities and supports simulations where bars form early in massive dynamically cold disks. It also suggests that if these bars at lookback times of 8–11 Gyr survive out to present epochs, bar-driven secular processes may operate over a long time and have a significant impact on some galaxies by z ∼ 0.</p
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On the stellar populations of galaxies at z = 9-11: the growth of metals and stellar mass at early times
We present a detailed stellar population analysis of 11 bright (H < 26.6) galaxies at z = 9-11 (three spectroscopically confirmed) to constrain the chemical enrichment and growth of stellar mass of early galaxies. We use the flexible Bayesian spectral energy distribution (SED) fitting code Prospector with a range of star formation histories (SFHs), a flexible dust attenuation law, and a self-consistent model of emission lines. This approach allows us to assess how different priors affect our results and how well we can break degeneracies between dust attenuation, stellar ages, metallicity, and emission lines using data that probe only the rest-frame ultraviolet (UV) to optical wavelengths. We measure a median observed UV spectral slope ß=-1.87-0.43+0.35 for relatively massive star-forming galaxies ( 9 10
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CEERS key paper. II. A first look at the resolved host properties of AGN at 3 < z < 5 with JWST
We report on the host properties of five X-ray-luminous active galactic nuclei (AGN) identified at 3 3 is significant because a rapid feedback mechanism is required in most semianalytic models and cosmological simulations to explain the growing population of massive quiescent galaxies observed at these redshifts. Our findings show that AGN can continue to inject energy into these systems after their star formation is curtailed, potentially heating their halos and preventing renewed star formation. Additional observations will be needed to determine what role this feedback may play in helping to quench these systems and/or maintain their quiescent state
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CEERS key paper. I. An early look into the first 500 Myr of galaxy formation with JWST
We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z ~ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin2, to search for candidate galaxies at z > 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z ~ 9-16. These objects are compact with a median half-light radius of ~0.5 kpc. We present an early estimate of the z ~ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M UV ~ -20 appears to evolve very little from z ~ 9 to 11. We also find that the abundance (surface density [arcmin-2]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z > 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultrahigh-redshift galaxies with which to further explore these conclusions.</p
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CEERS key paper. III. The diversity of galaxy structure and morphology at z = 3–9 with JWST
We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z = 3-9 using early James Webb Space Telescope (JWST) CEERS NIRCam observations. Our sample consists of 850 galaxies at z > 3 detected in both Hubble Space Telescope (HST)/WFC3 and CEERS JWST/NIRCam images, enabling a comparison of HST and JWST morphologies. We conduct a set of visual classifications, with each galaxy in the sample classified three times. We also measure quantitative morphologies across all NIRCam filters. We find that galaxies at z > 3 have a wide diversity of morphologies. Galaxies with disks make up 60% of galaxies at z = 3, and this fraction drops to ~30% at z = 6-9, while galaxies with spheroids make up ~30%-40% across the redshift range, and pure spheroids with no evidence for disks or irregular features make up ~20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (~40%-50%), while those that are purely irregular increases from ~12% to ~20% at z > 4.5. We note that these are apparent fractions, as many observational effects impact the visibility of morphological features at high redshift. On average, Spheroid-only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than disk or irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study, and further work with large samples at higher redshift is needed to quantify when these features first formed
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Dusty starbursts masquerading as ultra-high redshift galaxies in JWST CEERS observations
Lyman-break galaxy (LBG) candidates at z ? 10 are rapidly being identified in James Webb Space Telescope (JWST)/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (z ? 7) may also mimic the near-infrared (near-IR) colors of z > 10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z ˜ 5.1. We also present a tentative 2.6s SCUBA-2 detection at 850 µm around a recently identified z ˜ 16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z ~ 5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z ~ 4-6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra-high redshift LBG candidates from JWST observations.</p