CLASSY V: The Impact of Aperture Effects on the Inferred Nebular Properties of Local Star-forming Galaxies

Karla Z. Arellano-Córdova, Matilde Mingozzi, Danielle A. Berg, Bethan L. James, Noah S.J. Rogers, Alessandra Aloisi, Ricardo O. Amorín, Jarle Brinchmann, Stéphane Charlot, John Chisholm, Timothy Heckman, Stefany Fabian Dubón, Matthew Hayes, Svea Hernandez, Tucker Jones, Nimisha Kumari, Claus Leitherer, Crystal L. Martin, Themiya Nanayakkara, Richard W. PoggeRyan Sanders, Peter Senchyna, Evan D. Skillman, Dan P. Stark, Aida Wofford, Xinfeng Xu

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. However, different observational setups can affect these lines, and the derivation of the physical nebular properties. We analyze 12 local star-forming galaxies from the COS Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. We compare optical spectra observed with the Sloan Digital Sky Survey Data Release aperture, which has a 3″ diameter similar to COS, IFU, and long-slit spectra, including new LBT/MODS observations of five CLASSY galaxies. We calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (EWs). We find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. However, using IFU observations of three galaxies, we find that the E(B - V) values derived from the Balmer ratios decrease (by up to 53%) with increasing aperture size. The values change most significantly in the center of the galaxies, and level out near the COS aperture diameter of 2.″5. We examine the relative contributions from the gas and stars using the Hα and [O iii] λ5007 EWs as a function of aperture light fraction, but find little to no variations within a given galaxy. These results imply that the optical spectra provide nebular properties appropriate for the far-UV CLASSY spectra, even when narrow 1.″0 long-slit observations are used.

Original languageEnglish
Article number74
JournalAstrophysical Journal
Issue number2
StatePublished - Aug 1 2022

Bibliographical note

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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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