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Title: The COS Legacy Archive Spectroscopy Survey (CLASSY) Treasury Atlas*
Abstract

Far-ultraviolet (FUV; ∼1200–2000 Å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of the James Webb Space Telescope will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before; however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any FUV spectral database. We present the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) treasury and its first high-level science product, the CLASSY atlas. CLASSY builds on the Hubble Space Telescope (HST) archive to construct the first high-quality (S/N1500 Å≳ 5/resel), high-resolution (R∼ 15,000) FUV spectral database of 45 nearby (0.002 <z< 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY sample covers a broad range of properties including stellar more » mass (6.2 < logM(M) < 10.1), star formation rate (−2.0 < log SFR (Myr−1) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O32< 38.0), reddening (0.02 <E(BV) < 0.67), and nebular density (10 <ne(cm−3) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with thez∼ 0 mass–metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar toz≳ 2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.

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Authors:
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Publication Date:
NSF-PAR ID:
10375650
Journal Name:
The Astrophysical Journal Supplement Series
Volume:
261
Issue:
2
Page Range or eLocation-ID:
Article No. 31
ISSN:
0067-0049
Publisher:
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation
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