CLASSY IV. Exploring UV Diagnostics of the Interstellar Medium in Local High-z Analogs at the Dawn of the JWST Era

Matilde Mingozzi, Bethan L. James, Karla Z. Arellano-Córdova, Danielle A. Berg, Peter Senchyna, John Chisholm, Jarle Brinchmann, Alessandra Aloisi, Ricardo O. Amorín, Stéphane Charlot, Anna Feltre, Matthew Hayes, Timothy Heckman, Alaina Henry, Svea Hernandez, Nimisha Kumari, Claus Leitherer, Mario Llerena, Crystal L. Martin, Themiya NanayakkaraSwara Ravindranath, Evan D. Skillman, Yuma Sugahara, Aida Wofford, Xinfeng Xu

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22 Scopus citations


The Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY (CLASSY) provides the first high-resolution spectral catalog of 45 local high-z analogs in the ultraviolet (UV; 1200-2000 Å) to investigate their stellar and gas properties. Here we present a toolkit of UV interstellar medium (ISM) diagnostics, analyzing the main emission lines of CLASSY spectra (N iv] λ λ1483,87, C iv λλ1548,51, He ii λ1640, O iii]λ λ1661,6, Si iii] λλ1883,92, C iii] λ1907,9). Specifically, our aim is to provide accurate diagnostics for the reddening E(B − V), electron density n e , electron temperature T e , metallicity 12+log(O/H), and ionization parameter log(U), taking the different ISM ionization zones into account. We calibrate our UV toolkit using well-known optical diagnostics, analyzing archival optical spectra for all CLASSY targets. We find that UV density diagnostics estimate n e values that are ∼1-2 dex higher (e.g., n e (C iii]λ λ1907,9) ∼ 104 cm−3) than those inferred from their optical counterparts (e.g., n e ([S ii]λ λ6717,31) ∼ 102 cm−3; n e ([Ar iv]λ λ4714,41) ∼ 103 cm−3). T e derived from the hybrid ratio [O iii] λ1666/λ5007 proves to be reliable, implying differences in determining 12+log(O/H) compared to the optical counterpart O iii] λ4363/[O iii] λ5007 within ∼ ±0.3 dex. We also investigate the relation between the stellar and gas E(B − V), finding consistent values at high specific star formation rates (sSFRs; log ( sSFR ) ≳ − 8 yr−1), while at low sSFRs we confirmed an excess of dust attenuation in the gas. Finally, we investigate UV line ratios and equivalent widths to provide correlations with 12+log(O/H) and log(U), but note that there are degeneracies between the two. With this suite of UV-based diagnostics, we illustrate the pivotal role CLASSY plays in understanding the chemical and physical properties of high-z systems that JWST can observe in the rest-frame UV.

Original languageEnglish (US)
Article number110
JournalAstrophysical Journal
Issue number2
StatePublished - Nov 1 2022

Bibliographical note

Funding Information:
We thank the anonymous referee for their comments and advice, which helped improve the quality of the paper. M.M., D.A.B., and X.X. are grateful for the support for this program, HST-GO-15840, that was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Associations of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Also, M.M. is grateful to Carlo Cannarozzo for inspiring conversations and advice. B.L.J., S.H., and N.K. are thankful for support from the European Space Agency (ESA). A.F. acknowledges the support from grant PRIN MIUR2017-20173ML3WW_001. A.W. acknowledges the support of UNAM via grant agreement PAPIIT no. IN106922. R.A. acknowledges support from ANID Fondecyt Regular 1202007.

Funding Information:
Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III website is . SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.

Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.


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