New study says stellar mass of galaxies does not contain all the information about other galactic properties, refuting a major presumption in astronomy

Cosmologists from Visva-Bharati University and Osmania University reported that the stellar mass of galaxies does not encode all of the information about other galactic properties, an assumption long thought to be true. The new study used archival data from the SDSS in conjunction with cosmological simulations to come to this groundbreaking conclusion.

An artist’s impression of the Milky Way galaxy. Photograph: Chen Xiaodian.

Downloaded from: The Guardian

Understanding the formation and evolution of galaxies is undoubtedly one of the major goals of modern cosmology. The integrated stellar mass of a galaxy is thought to be the most fundamental property which largely influences its structure and evolution. It is often taken as an impression of its formation history and governs its future evolution. Galaxies assemble gas through both mergers and as well as various secular processes. This gas upon condensation gives rise to molecular clouds which in turn become stellar nurseries. Hence, high stellar mass represents more evolved systems. Furthermore, the stellar mass of a galaxy correlates with other galactic properties, such as star formation rate, metallicity, and halo mass. Thus, different scaling relations involving stellar-mass coupled with the galaxy stellar mass function (GSMF), are hypothesized to pose salient constraints for the formation and evolutionary models of galaxies.

However, what was missing in previous studies was a comprehensive analysis regarding the extent up to which stellar mass of galaxies control the galactic properties and therefore influence galactic evolution.

In this study, the cosmologists investigated the possibility that prior knowledge of the stellar mass of galaxies may explain the Mutual Information (MI) between environment and morphology. To investigate this, the authors employed a unique and robust method known as the information-theoretic framework developed C. Shannon in 1948 to the publicly available SDSS DR16 and compared the results against semi-analytic models implemented on the Millennium simulation.

The study reported a noteworthy difference between all the theoretical models with observations, something very unusual given the fact that these models are constructed and severely fine-tuned to fit the observations. However, the study does not answer the question that if the stellar mass of galaxies is indeed not the most important parameter deciding the fate of galaxies, that what does? The study is nonetheless revolutionary and insists on follow up research to understand this conundrum.

The new study has been published in the Journal of Cosmology and Astroparticle Physics.

Article Information: S. Bhattacharjee, B. Pandey, S. Sarkar, "Can a conditioning on stellar mass explain the mutual information between morphology and environment?" JCAP, 09 039 (2020); arXiv: 2004.05016

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