81 research outputs found
Low-mass bursty galaxies in JADES efficiently produce ionising photons and could represent the main drivers of reionisation
© 2023 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We study galaxies in JADES Deep to study the evolution of the ionising photon production efficiency, , observed to increase with redshift. We estimate for a sample of 677 galaxies at using NIRCam photometry. Specifically, combinations of the medium and wide bands F335M-F356W and F410M-F444W to constrain emission lines that trace : H and [OIII]. Additionally, we use the spectral energy distribution fitting code \texttt{Prospector} to fit all available photometry and infer galaxy properties. The flux measurements obtained via photometry are consistent with FRESCO and NIRSpec-derived fluxes. Moreover, the emission-line-inferred measurements are in tight agreement with the \texttt{Prospector} estimates. We also confirm the observed trend with redshift and M, and find: . We use \texttt{Prospector} to investigate correlations of with other galaxy properties. We see a clear correlation between and burstiness in the star formation history of galaxies, given by the ratio of recent to older star formation, where burstiness is more prevalent at lower stellar masses. We also convolve our relations with luminosity functions from the literature, and constant escape fractions of 10 and 20\%, to place constraints on the cosmic ionising photon budget. By combining our results, we find that if our sample is representative of the faint low-mass galaxy population, galaxies with bursty star formation are efficient enough in producing ionising photons and could be responsible for the reionisation of the Universe.Peer reviewe
In-orbit Performance of the Near-infrared Spectrograph NIRSpec on the James Webb Space Telescope
The Near-Infrared Spectrograph (NIRSpec) is one of the four focal plane instruments on the James Webb Space Telescope. In this paper, we summarize the in-orbit performance of NIRSpec, as derived from data collected during its commissioning campaign and the first few months of nominal science operations. More specifically, we discuss the performance of some critical hardware components such as the two NIRSpec Hawaii-2RG detectors, wheel mechanisms, and the microshutter array. We also summarize the accuracy of the two target acquisition procedures used to accurately place science targets into the slit apertures, discuss the current status of the spectrophotometric and wavelength calibration of NIRSpec spectra, and provide the "as measured" sensitivity in all NIRSpec science modes. Finally, we point out a few important considerations for the preparation of NIRSpec science programs
JWST NIRCam + NIRSpec: Interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs
We present an interstellar medium and stellar population analysis of three spectroscopically confirmed z > 7 galaxies in the Early Release Observations JWST/NIRCam and JWST/NIRSpec data of the SMACS J0723.3-7327 cluster. We use the Bayesian spectral energy distribution-fitting code PROSPECTOR with a flexible star formation history (SFH), a variable dust attenuation law, and a self-consistent model of nebular emission (continuum and emission lines). Importantly, we self-consistently fit both the emission line fluxes from JWST/NIRSpec and the broad-band photometry from JWST/NIRCam, taking into account slit-loss effects. We find that these three z=7.6-8.5 galaxies (M-* approximate to 10(8) M-circle dot) are young with rising SFHs and mass-weighted ages of 3-4 Myr, though we find indications for underlying older stellar populations. The inferred gas-phase metallicities broadly agree with the direct metallicity estimates from the auroral lines. The galaxy with the lowest gas-phase metallicity (Z(gas) = 0.06 Z(circle dot)) has a steeply rising SFH, is very compact ( <0.2 kpc), and has a high star formation rate surface density (Sigma(SFR) approximate to 22 M-circle dot yr(-1) kpc(-2)), consistent with rapid gas accretion. The two other objects with higher gas-phase metallicities show more complex multicomponent morphologies on kpc scales, indicating that their recent increase in star formation rate is driven by mergers or internal, gravitational instabilities. We discuss effects of assuming different SFH priors or only fitting the photometric data. Our analysis highlights the strength and importance of combining JWST imaging and spectroscopy for fully assessing the nature of galaxies at the earliest epochs
Discovery and properties of the earliest galaxies with confirmed distances
© 2023 Springer Nature Limited. This is the accepted manuscript version of an article which has been published in final form at 10.1038/s41550-023-01921-1Surveys with James Webb Space Telescope (JWST) have discovered candidate galaxies in the first 400 Myr of cosmic time. The properties of these distant galaxies provide initial conditions for understanding early galaxy formation and cosmic reionisation. Preliminary indications have suggested these candidate galaxies may be more massive and abundant than previously thought. However, without spectroscopic confirmation of their distances to constrain their intrinsic brightnesses, their inferred properties remain uncertain. Here we report on four galaxies located in the JWST Advanced Deep Extragalactic Survey (JADES) Near-Infrared Camera (NIRCam) imaging with photometric redshifts subsequently confirmed by JADES JWST Near- Infrared Spectrograph (NIRSpec) observations. These galaxies include the first redshift systems both discovered and spectroscopically confirmed by JWST. Using stellar population modelling, we find the galaxies typically contain a hundred million solar masses in stars, in stellar populations that are less than one hundred million years old. The moderate star formation rates and compact sizes suggest elevated star formation rate surface densities, a key indicator of their formation pathways. Taken together, these measurements show that the first galaxies contributing to cosmic reionisation formed rapidly and with intense internal radiation fields.Peer reviewe
The ionizing photon production efficiency at z ∼6 for Lyman-Alpha emitters using JEMS and MUSE
We study the ionizing photon production efficiency at the end of the Epoch of Reionization (z ∼5.4-6.6) for a sample of 30 Ly α emitters. This is a crucial quantity to infer the ionizing photon budget of the universe. These objects were selected to have reliable spectroscopic redshifts, assigned based on the profile of their Ly α emission line, detected in the MUSE deep fields. We exploit medium-band observations from the JWST Extragalactic Medium-band Survey (JEMS) to find the flux excess corresponding to the redshifted Hα emission line. We estimate the ultraviolet (UV) luminosity by fitting the full JEMS photometry, along with several HST photometric points, with Prospector. We find a median UV continuum slope of, indicating young stellar populations with little-To-no dust attenuation. Supported by this, we derive ζion,0 with no dust attenuation and find a median value of log. If we perform dust attenuation corrections and assume a Calzetti attenuation law, our values are lowered by ∼0.1 dex. Our results suggest Ly α emitters at the Epoch of Reionization have slightly enhanced ζion,0 compared to previous estimations from literature, in particular, when compared to the non-Ly α emitting population. This initial study provides a promising outlook on the characterization of ionizing photon production in the early universe. In the future, a more extensive study will be performed on the entire data set provided by the JWST Advanced Deep Extragalactic Survey (JADES). Thus, for the first time, allowing us to place constraints on the wider galaxy populations driving reionization
The Physical Conditions of Emission-Line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations
We present rest-frame optical emission-line flux ratio measurements for five
galaxies observed by the JWST Near-Infared Spectrograph (NIRSpec) in the
SMACS 0723 Early Release Observations. We add several quality-control and
post-processing steps to the NIRSpec pipeline reduction products in order to
ensure reliable relative flux calibration of emission lines that are closely
separated in wavelength, despite the uncertain \textit{absolute}
spectrophotometry of the current version of the reductions. Compared to
galaxies in the literature, the galaxies have similar
[OIII]5008/H ratios, similar [OIII]4364/H
ratios, and higher (0.5 dex) [NeIII]3870/[OII]3728
ratios. We compare the observations to MAPPINGS V photoionization models and
find that the measured [NeIII]3870/[OII]3728,
[OIII]4364/H, and [OIII]5008/H emission-line
ratios are consistent with an interstellar medium that has very high ionization
(, units of cm~s), low metallicity (), and very high pressure (, units of
cm). The combination of [OIII]4364/H and
[OIII](4960+5008)/H line ratios indicate very high electron
temperatures of , further implying metallicities of
with the application of low-redshift calibrations for
``-based'' metallicities. These observations represent a tantalizing new
view of the physical conditions of the interstellar medium in galaxies at
cosmic dawn.Comment: Accepted for publication in AAS Journals. 14 pages, 6 figures, 3
table
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies
JADES: Detecting [OIII] λ 4363 emitters and testing strong line calibrations in the high- z Universe with ultra-deep JWST/NIRSpec spectroscopy up to z ~ 9.5
We present ten novel [OIII]λ4363 auroral line detections up to z~ 9.5 measured from ultra-deep JWST/NIRSpec MSA spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES). We leverage the deepest spectroscopic observations taken thus far with NIRSpec to determine electron temperatures and oxygen abundances using the direct Te method. We directly compare these results against a suite of locally calibrated strong-line diagnostics and recent high-z calibrations. We find the calibrations fail to simultaneously match our JADES sample, thus warranting a self-consistent revision of these calibrations for the high-z Universe. We find a weak dependence between R2 and O3O2 with metallicity, thus suggesting these line ratios are inefficient in the high-z Universe as metallicity diagnostics and degeneracy breakers. We find R3 and R23 are still correlated with metallicity, but we find a tentative flattening of these diagnostics, thus suggesting future difficulties when applying these strong line ratios as metallicity indicators in the high-z Universe. We also propose and test an alternative diagnostic based on a different combination of R3 and R2 with a higher dynamic range. We find a reasonably good agreement (median offset of 0.002 dex, median absolute offset of 0.13 dex) with the JWST sample at low metallicity, but future investigations are required on larger samples to probe past the turnover point. At a given metallicity, our sample demonstrates higher ionization and excitation ratios than local galaxies with rest-frame EWs(Hβ) ≈ 200-300 Å. However, we find the median rest-frame EWs(Hβ) of our sample to be~2× less than the galaxies used for the local calibrations. This EW discrepancy combined with the high ionization of our galaxies does not offer a clear description of [OIII]λ4363 production in the high-z Universe, thus warranting a much deeper examination into the factors influencing these processes
JADES: Insights into the low-mass end of the mass-metallicity-SFR relation at 3 < z < 10 from deep JWST/NIRSpec spectroscopy*
We analysed the gas-phase metallicity properties of a sample of low-stellar-mass (log M?/M. 9) galaxies at 3 6, with galaxies significantly less enriched than predicted given their M? and SFR (with a median offset in log(O/H) of ∼0.5 dex, significant at ∼5σ). These observations are consistent with an enhanced stochasticity in the gas accretion and star-formation history of high-redshift systems, prompting us to reconsider the nature of the relationship between M?, O/H, and SFR in the early Universe
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