CECILIA: The Faint Emission Line Spectrum of z ∼ 2–3 Star-forming Galaxies
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Northwestern University
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Carnegie Observatories
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Franklin & Marshall College
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University of Copenhagen
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University of Wisconsin–Madison
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University of Minnesota
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California Institute of Technology
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University of California, Davis
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Space Telescope Science Institute
Abstract
e 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 at z ∼ 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 ([N ii]λ5756, [S iii]λ6313, and [O ii]λλ7322, 7332), as well as other semi-strong and faint emission lines, including forbidden [Ni ii]λλ7380, 7414 and permitted O iλ8449, some of which have never before been observed outside of the local Universe. Using these measurements, we find Te[N ii] = 13,630 ± 2540 K, representing the first measurement of electron temperature using [N ii] in the high-redshift Universe. We also see evidence for broad line emission with a FWHM of 536−167+45 km s−1; the broad component of Hα is 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.
Copyright and License
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
The authors thank Jane Rigby, Taylor Hutchison, and Marcia Rieke for their advice regarding the reduction of the JWST data, as well as Jenny Greene for her input on the scope of the discussion. We are also grateful to the JWST/NIRSpec team for their ongoing work to support this complex and powerful instrument.
Funding
A.L.S., G.C.R., and R.F.T. acknowledge partial support from the JWST-GO-02593.008-A, JWST-GO-02593.004-A, and JWST-GO-02593.006-A grants, respectively. R.F.T. also acknowledges support from the Pittsburgh Foundation (grant ID UN2021-121482) and the Research Corporation for Scientific Advancement (Cottrell Scholar Award, grant ID 28289).
Data Availability
This work is primarily based on observations made with NASA/ESA/CSA JWST, associated with PID 2593, which can be accessed via doi:10.17909/x66z-p144. The data were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST.
Some of the data used to generate the original line flux predictions were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation, and the authors wish to recognize and acknowledge the significant cultural role and reverence that the summit of Maunakea has within the indigenous Hawaiian community.
Facilities
JWST (NIRSpec) - James Webb Space Telescope.
Software References
BPASSv2 (Stanway et al. 2016; Eldridge et al. 2017), Cloudy (Ferland et al. 2013), GalDNA (Strom et al. 2018), JWST Calibration Pipeline (Bushouse et al. 2023), grizli (Brammer 2023), msaexp (Brammer 2022), PyNeb (Luridiana et al. 2015).
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Additional details
- Space Telescope Science Institute
- JWST-GO-02593.008-A
- Space Telescope Science Institute
- JWST-GO-02593.004-A
- Space Telescope Science Institute
- WST-GO-02593.006-A
- Pittsburgh Foundation
- UN2021-121482
- Research Corporation for Science Advancement
- Cottrell Scholar Award
- Accepted
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2023-10-23Accepted
- Available
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2023-11-20Published online
- Caltech groups
- Astronomy Department