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1. Aperture and Resolution Effects on Ultraviolet Star-forming Properties: Insights from Local Galaxies and Implications for High-redshift Observations

Author

Ilyse Clark, Danielle A. Berg, Claus Leitherer, Karla Z. Arellano-Córdova, and Andreas A. C. Sander

Subjects
Ultraviolet astronomy, Galaxy evolution, Galaxy abundances, Astrophysics, QB460-466
Abstract

We present an analysis of the effects of spectral resolution and aperture scale on derived galaxy properties using far-ultraviolet (FUV) spectra of local star-forming galaxies from the International Ultraviolet Explorer ( R ∼ 250, field of view (FOV) ∼ 10″ × 20″) and Cosmic Origins Spectrograph on the Hubble Space Telescope ( R ∼ 15,000, FOV ∼ 2.″5). Using these spectra, we measured FUV luminosities, spectral slopes, dust attenuation, and equivalent widths. We find that galaxies with one dominant stellar cluster have FUV properties that are independent of aperture size, while galaxies with multiple bright clusters are sensitive to the total light fraction captured by the aperture. Additionally, we find significant correlations between the strength of stellar and interstellar absorption lines and metallicity, indicating metallicity-dependent line-driven stellar winds and interstellar macroscopic gas flows shape stellar and interstellar spectral lines, respectively. The observed line strength versus metallicity relation of stellar-wind lines agrees with the prediction of population synthesis models for young starbursts. In particular, measurements of the strong stellar C iv λλ 1548, 1550 line provide an opportunity to determine stellar abundances as a complement to gas-phase abundances. We provide a relation between the equivalent width of the C iv line and the oxygen abundance of the galaxy. We discuss this relation in terms of the stellar-wind properties of massive stars. As the driving lines in stellar winds are mostly ionized iron species, the C iv line may eventually offer a method to probe α -element-to-iron ratios in star-forming galaxies once consistent models with nonsolar abundance ratios are available. These results have important implications for the galaxy-scale, low-resolution observations of high-redshift galaxies from JWST ( R ∼ 100–3500).

Published
2024
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2. CLASSY. II. A Technical Overview of the COS Legacy Archive Spectroscopic Survey

Author

Bethan L. James, Danielle A. Berg, Teagan King, David J. Sahnow, Matilde Mingozzi, John Chisholm, Timothy Heckman, Crystal L. Martin, Dan P. Stark, Alessandra Aloisi, Ricardo O. Amorín, Karla Z. Arellano-Córdova, Matthew B. Bayliss, Rongmon Bordolo, Jarle Brinchmann, Stéphane Charlot, Zuyi Chen, Jacopo Chevallard, Ilyse Clark, Dawn K. Erb, Anna Feltre, Matthew Hayes, Alaina Henry, Svea Hernandez, Anne Jaskot, Lisa J. Kewley, Nimisha Kumari, Claus Leithere, Mario Llerena, Michael Maseda, Themiya Nanayakkara, Masami Ouch, Adele Plat, Richard W. Pogge, Swara Ravindranath, Jane R. Rigby, Claudia Scarlata, Peter Senchyna, Evan D. Skillman, Charles C. Steidel, Allison L. Strom, Yuma Sugahara, Stephen M. Wilkins, Aida Wofford, and Xinfeng Xu

Subjects
Astrophysics
Abstract

The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies that were chosen to cover similar properties to those seen at high z (z > 6). The prime high-level science product of CLASSY is accurately coadded UV spectra, ranging from ∼1000 to 2000 Å, derived from a combination of archival and new data obtained with HST's Cosmic Origins Spectrograph (COS). This paper details the multistage technical processes of creating this prime data product and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet and near-ultraviolet (NUV) spectra. We provide guidelines on how to successfully utilize COS observations of extended sources, despite COS being optimized for point sources, and best-practice recommendations for the coaddition of UV spectra in general. Moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the CLASSY data. In particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of NUV spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via C iii] nebular emission. Despite changes in spectral resolution of up to ∼25% between individual data sets (due to changes in the COS line-spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in part to our signal-to-noise regime of S/N < 20.

Published
2022
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3. The COS Legacy Archive Spectroscopy Survey (CLASSY) Treasury Atlas

Author

Danielle A. Berg, Bethan L. James, Teagan King, Meaghan McDonald, Zuyi Chen, John Chisholm, Timothy Heckman, Crystal L. Martin, Dan P. Stark, Alessandra Aloisi, Ricardo O. Amorín, Karla Z. Arellano-Córdova, Matthew Bayliss, Rongmon Bordoloi, Jarle Brinchmann, Stéphane Charlot, Jacopo Chevallard, Ilyse Clark, Dawn K. Erb, Anna Feltre, Max Gronke, Matthew Hayes, Alaina Henry, Svea Hernandez, Anne Jaskot, Tucker Jones, Lisa J. Kewley, Nimisha Kumari, Claus Leitherer, Mario Llerena, Michael Maseda, Matilde Mingozzi, Themiya Nanayakkara, Masami Ouchi, Adele Plat, Richard W. Pogge, Swara Ravindranath, Jane R. Rigby, Ryan Sanders, Claudia Scarlata, Peter Senchyna, Evan D. Skillman, Charles C. Steidel, Allison L. Strom, Yuma Sugahara, Stephen M. Wilkins, Aida Wofford, and Xinfeng Xu

Subjects
Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies
Abstract

Far-ultraviolet (FUV; ~1200-2000 angstroms) 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 JWST 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 COS Legacy Spectroscopic SurveY (CLASSY) treasury and its first high level science product, the CLASSY atlas. CLASSY builds on the HST archive to construct the first high-quality (S/N_1500 >~ 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 mass (6.2 < logM_star(M_sol) < 10.1), star formation rate (-2.0 < log SFR (M_sol/yr) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O_32 < 38.0), reddening (0.02 < E(B-V < 0.67), and nebular density (10 < n_e (cm^-3) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with z~0 mass-metallicity relationship, but is offset to higher SFRs by roughly 2 dex, similar to z >~2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time., Accepted for publication in ApJ

Published
2022

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