The effect of spiral arms on the Sérsic photometry of galaxies

Journal Article · 28 February 2022 · Astronomy and Astrophysics

DOI: https://doi.org/10.1051/0004-6361/202142786 · OSTI ID:1982326

Sonnenfeld, Alessandro  ^[1]

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1. Leiden Univ. (Netherlands). Leiden Observatory

The Sérsic profile is a widely used model for describing the surface brightness distribution of galaxies. Spiral galaxies, however, are qualitatively different from a Sérsic model. Aims. The goal of this study is to assess how accurately the total flux and half-light radius of a galaxy with spiral arms can be recovered when fitted with a Sérsic profile. Methods. I selected a sample of bulge-dominated galaxies with spiral arms. Using photometric data from the Hyper Suprime-Cam survey, I estimated the contribution of the spiral arms to their total flux. Then I generated simulated images of galaxies with similar characteristics, fitted them with a Sérsic model, and quantified the error on the determination of the total flux and half-light radius. Results. Spiral arms can introduce biases on the photometry of galaxies in a way that depends on the underlying smooth surface brightness profile, the location of the arms, and the depth of the photometric data. A set of spiral arms accounting for 10% of the flux of a bulge-dominated galaxy typically causes the total flux and the half-light radius to be overestimated by 15% and 30%, respectively. This bias, however, is much smaller if the galaxy is disk-dominated. Conclusions. Galaxies with a prominent bulge and a non-zero contribution from spiral arms are the most susceptible to biases in the total flux and half-light radius when fitted with a Sérsic profile. If photometric measurements with high accuracy are required, then measurements over finite apertures are to be preferred over global estimates of the flux.

• Research Organization: Leiden Univ. (Netherlands). Leiden Observatory; US Department of Energy (USDOE), Washington, DC (United States). Office of Science, Sloan Digital Sky Survey (SDSS)
• Sponsoring Organization: ASIAA; FIRST program, Japanese Cabinet Office; Japan Science and Technology Agency (JST); Japan Society for the Promotion of Science (JSPS); KEK; Ministry of Education, Culture, Sports, Science and Technology (MEXT); NAOJ, Kavli IPMU; Princeton University; Toray Science Foundation; USDOE Office of Science (SC)
• OSTI ID: 1982326
• Journal Information: Astronomy and Astrophysics, Journal Name: Astronomy and Astrophysics Vol. 659; ISSN 0004-6361
• Publisher: EDP SciencesCopyright Statement
• Country of Publication: United States
• Language: English