What determines the maximum stellar surface density in galaxies?

Chih-Teng Ling^1*, Tetsuya Hashimoto², Tomotsugu Goto²

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Institute of Astronomy, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Chih-Teng Ling, email:jimmy871201@gmail.com

Observationally, there exists the universal maximum stellar surface density, across wide scale range of ~8 orders of stellar mass from star cluster to galaxy. This suggests the existence of the fundamental physics which regulates the star formation and stellar density. Grudić et al. (2018) suggested a theory to explain the universal maximum stellar surface density Σ_max based on collapsing star-forming gas cloud, where Σ represents stellar surface density. Here we show that the Σ_max in galaxies depends on the stellar mass. Our galaxy sample is selected from the Sloan Digital Sky Survey Data Release 12 at z = 0.05 - 0.5. The maximum limit of Σ has a strong dependency on the stellar mass especially for low mass galaxies of ~10⁹M_☉ in contrast to a constant maximum predicted by theoretical models. We also find that high-Σ galaxies have different distribution of the color and star formation rate, which depends on the stellar mass as well. The high-Σ galaxies between 10⁹M_☉ - 10¹⁰M_☉ show a redder color than the normal galaxies, which suggests that these galaxies reach the Σ_max as the consequence of the galaxy evolution from blue star-forming to red quiescent in this stellar mass range. Our results suggest the theories on the maximum surface stellar density must be re-written.

Keywords: galaxies: fundamental parameters, galaxies: evolution