Abstract
The outskirts of galaxies have been studied from multiple perspectives for the past few decades. However, it is still unknown if all galaxies have clear-cut edges similar to everyday objects. We address this question by developing physically motivated criteria to define the edges of galaxies. Based on the gas density threshold required for star formation, we define the edge of a galaxy as the outermost radial location associated with a significant drop in either past or ongoing in situ star formation. We explore ∼1000 low-inclination galaxies with a wide range in morphology (dwarfs to ellipticals) and stellar mass (107 M⊙ < M⋆ < 1012 M⊙). The location of the edges of these galaxies (Redge) were visually identified as the outermost cutoff or truncation in their radial profiles using deep multi-band optical imaging from the IAC Stripe82 Legacy Project. We find this characteristic feature at the following mean stellar mass density, which varies with galaxy morphology: 2.9 ± 0.10 M⊙ pc−2 for ellipticals, 1.1 ± 0.04 M⊙ pc−2 for spirals, and 0.6 ± 0.03 M⊙ pc−2 for present-day star-forming dwarfs. Additionally, we find that Redge depends on its age (colour) where bluer galaxies have larger Redge at a fixed stellar mass. The resulting stellar mass–size plane using Redge as a physically motivated galaxy size measure has a very narrow intrinsic scatter (≲0.06 dex). These results highlight the importance of new deep imaging surveys to explore the growth of galaxies and trace the limits of star formation in their outskirts.
Funder
Knut and Alice Wallenberg Foundation
State Research Agency (AEI-MCINN) of the Spanish Ministry of Science and Innovation
Ministry of Science and Innovation, through the State Budget and by the Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community
ACIISI, Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund
Subject
Space and Planetary Science,Astronomy and Astrophysics
Cited by
8 articles.
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