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Abstract We present the first results from Chemical Evolution Constrained Using Ionized Lines in Interstellar Aurorae (CECILIA), a Cycle 1 JWST NIRSpec/MSA program that uses ultra-deep ∼30 hr G235M/F170LP observations to target multiple electron temperature-sensitive auroral lines in the spectra of 33 galaxies atz∼ 1–3. Using a subset of 23 galaxies, we construct two ∼600 object-hour composite spectra, both with and without the stellar continuum, and use these to investigate the characteristic rest-optical (λrest≈ 5700–8500 Å) spectrum of star-forming galaxies at the peak epoch of cosmic star formation. Emission lines of eight different elements (H, He, N, O, Si, S, Ar, and Ni) are detected, with most of these features observed to be ≲3% the strength of Hα. We report the characteristic strength of three auroral features ([Nii]λ5756, [Siii]λ6313, and [Oii]λλ7322, 7332), as well as other semi-strong and faint emission lines, including forbidden [Niii]λλ7380, 7414 and permitted Oiλ8449, some of which have never before been observed outside of the local Universe. Using these measurements, we findTe[Nii] = 13,630 ± 2540 K, representing the first measurement of electron temperature using [Nii] in the high-redshift Universe. We also see evidence for broad line emission with a FWHM of km s−1; the broad component of Hαis 6.01%–28.31% the strength of the narrow component and likely arises from star-formation-driven outflows. Finally, we briefly comment on the feasibility of obtaining large samples of faint emission lines using JWST in the future.more » « less
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Abstract The dispersion in chemical abundances provides a very strong constraint on the processes that drive the chemical enrichment of galaxies. Due to its proximity, the spiral galaxy M33 has been the focus of numerous chemical abundance surveys to study the chemical enrichment and dispersion in abundances over large spatial scales. The CHemical Abundances Of Spirals project has observed ∼100 Hiiregions in M33 with the Large Binocular Telescope (LBT), producing the largest homogeneous sample of electron temperatures (Te) and direct abundances in this galaxy. Our LBT observations produce a robust oxygen abundance gradient of −0.037 ± 0.007 dex kpc−1and indicate a relatively small (0.043 ± 0.015 dex) intrinsic dispersion in oxygen abundance relative to this gradient. The dispersions in N/H and N/O are similarly small, and the abundances of Ne, S, Cl, and Ar relative to O are consistent with the solar ratio as expected forα-process orα-process-dependent elements. Taken together, the ISM in M33 is chemically well-mixed and homogeneously enriched from inside out, with no evidence of significant abundance variations at a given radius in the galaxy. Our results are compared to those of the numerous studies in the literature, and we discuss possible contaminating sources that can inflate abundance dispersion measurements. Importantly, if abundances are derived from a singleTemeasurement andTe–Terelationships are relied on for inferring the temperature in the unmeasured ionization zone, this can lead to systematic biases that increase the measured dispersion up to 0.11 dex.more » « less