Dr Jacopo Chevallard

Abstract:

JWST has discovered an early period of galaxy formation that was more vigorous than expected, which has challenged our understanding of the early Universe. In this work, we present the longest spectroscopic integration ever acquired by JWST/MIRI (tobs ≈ 51 hr). This spectrum covers the brightest rest-frame optical nebular emission lines for the luminous galaxy JADES-GS-z14-0 at z = 14.18. Most notably, we detect [O III]λλ4959, 5007 at ≈14σ and Hα at ≈4σ with these ultradeep observations. These lines reveal that JADES-GS-z14-0 has low dust attenuation with a recent star formation rate of SFR ≈ 8 ± 2M⊙ yr−1, star formation rate surface density of ΣSFR ≈ 20 ± 5M⊙ yr−1 kpc−2, and ionizing photon production efficiency of ξion ≈ 1025.3±0.1 Hz erg−1. Using standard strong-line diagnostics, we infer a gas-phase oxygen abundance of log10(O/H)+12≈7.5±0.2 (≈6%Z⊙), carbon-to-oxygen ratio of [C/O] ≈ −0.4 ± 0.2, ionization parameter of log10(U)≳−2.4 , and density of nH ≈ 690 ± 200 cm−3. Using detailed photoionization modeling, we instead derive log10(O/H)+12≈8.5−0.4+0.4 (≈60%Z⊙), log10(U)≈−1.4−0.4+0.3 , and nH≈540−320+520cm−3 . The inferred properties of JADES-GS-z14-0 are similar to those measured for similarly luminous galaxies at z > 10 with previous MIRI/Spectroscopy, such as GHZ2/GLASSz12, GN-z11, and MACS0647-JD1. These results suggest extreme ionization conditions and rapid metal enrichment less than 300 Myr after the Big Bang. Existing simulations are unable to reproduce the empirical and inferred properties of JADES-GS-z14-0. This work demonstrates an important step toward understanding the formation of the first stars and heavy elements in the Universe. Future work will focus on the detection of the rest-frame optical continuum and its interpretation for the stellar population properties of JADES-GS-z14-0.

Abstract:

We present a sample of 2081 sources selected at a photometric redshift zphot > 8 across the JADES DR5 data release in GOODS-S and GOODS-N over a total area of 469 arcmin2. These sources range from MUV = −22 to MUV = −16, with 19 objects at zphot > 14. We estimate the UV slopes for the full sample from fits to the photometry and find evidence for a steepening of the relationship between the UV continuum slope and MUV to higher redshifts, a result that differs from prior analyses of brighter samples in the literature. We provide evidence that over one-quarter of our sources have evidence for being morphologically extended, with many galaxies showing multiple bright knots or clumps even out to z ∼ 13–14, an indication of how galaxies at cosmic dawn are growing and evolving. We discuss JADES-GN+189.15982+62.28899, a GOODS-N F200W dropout galaxy at zphot ∼ 15–18, which has been observed spectroscopically with JWST/NIRSpec in prism mode, resulting in a very low signal-to-noise spectrum that is consistent with the photometry and rules out a number of low-redshift solutions for the source. Finally, we use a subsample of 123 objects in our sample with spectroscopic redshifts to explore the usage of alternate fitting templates and a prescription for Lyα damping wing absorption, finding that both produce significant improvements to the estimated photometric redshifts.

Abstract:

This paper accompanies Data Release 4 of the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey, which presents the full NIRSpec spectroscopy of the survey. We provide spectra of 5190 targets across Great Observatories Origins Deep Survey (GOODS)-North and GOODS-South (including the Hubble Ultra Deep Field), observed with the low-dispersion (–300) prism and three medium-resolution () gratings spanning m; 2654 were also observed with the higher resolution () G395H grating. The tiered survey design obtained h exposures for galaxies in the Deep and Ultra Deep tiers, and shallower observations (–3 h per setting) of galaxies in the Medium tiers. Targets were selected from photometric redshifts or colours, with priority given to rest-UV-selected galaxies at and F444W-selected galaxies at . We describe the full target selection and present spectroscopic redshifts and success rates. In total, we obtain robust redshifts for 3297 galaxies, including 396 at and 2545 at . To facilitate uniform analyses, we define ‘gold’ subsamples based on UV- and F444W-selection. Using the parent samples and redshift success rates, we construct rest-UV luminosity functions at from the Medium- and Deep-JWST tiers. Our number densities agree well with previous determinations from both photometric and spectroscopic samples, with modest interloper fractions confirming the reliability of photometric UV-bright galaxy selections at these redshifts.

Abstract:

We present an overview of the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey (JADES), an ambitious program of infrared imaging and spectroscopy in the GOODS-S and GOODS-N deep fields, designed to study galaxy evolution from high redshift to cosmic noon. JADES uses about 770 hr of Cycle 1 guaranteed time largely from the Near-Infrared Camera (NIRCam) and Near-Infrared Spectrograph (NIRSpec) instrument teams. In GOODS-S, in and around the Hubble Ultra Deep Field and Chandra Deep Field South, JADES produces a deep imaging region of ∼42 arcmin2 with over 100 hr of exposure time spread over nine NIRCam filters, including two medium-band filters. This is extended at medium depth in GOODS-S and GOODS-N with NIRCam imaging of ∼167 arcmin2, averaging 25 hr of exposure over 8–10 filters. In both fields, we conduct extensive NIRSpec multiobject spectroscopy, including two deep pointings of 55 hr exposure time, 14 medium pointings of ∼12 hr, and 15 shallower pointings of ∼4 hr, targeting over 5000 Hubble Space Telescope– and JWST-detected faint sources with five low-, medium-, and high-resolution dispersers covering 0.6–5.3 μm. Finally, JADES extends redward via coordinated parallels with the JWST Mid-Infrared Instrument, featuring ∼10 arcmin2 with 43 hr of exposure at 7.7 μm and thrice that area with 1.4–6.8 hr of exposure at 12.8 and 15 μm. For nearly 30 yr, the GOODS-S and GOODS-N fields have been developed as the premier deep fields on the sky; JADES is now providing a compelling start on JWST's legacy in these fields.

Abstract:

We present gas-phase abundances of carbon (C), -elements (O, Ne, Si, and Ar), and iron (Fe) obtained from stacked spectra of high-z star-forming galaxies with the deep Near Infrared Spectrograph medium-resolution data from the James Webb Space Telescope Advanced Deep Extragalactic Survey. Our 564 sources at –7 have a median stellar mass of and a median star-formation rate of , placing them close to the star-formation main sequence. We find that the stacked spectrum of all our 564 sources has relatively low , moderate , and low values at a low gas-phase metallicity of (), suggesting dominant yields of core-collapse supernovae evolved from massive stars. The detection of a weak [Si iii] emission line in our stacked spectrum provides a silicon-to-oxygen abundance ratio of , which is lower than that of stars in the Milky Way disc and lower than expected by chemical evolution models, suggesting silicon depletion on to dust grains. Likewise, this Si/O value is lower than that we newly derive for two individual galaxies (GN-z11 and RXCJ2248) with negligible dust attenuation. By performing spectral stacking in bins of , star-formation rate (SFR), specific SFR (sSFR), and ultraviolet continuum slope , we identify [Fe iii] line detections in the high-sSFR bin and the blue- bin, both of which exhibit supersolar Fe/O ratios, while their C/O, Ar/O, and Si/O ratios are comparable to those of the all-sources stack. Our findings support a chemically young gas composition with rapid dust depletion in the general population of high-z star-forming galaxies, while raising the possibility of anomalous, selective Fe/O enhancement at the very early epoch of star formation.