Environment and mass dependencies of galactic $\lambda$ spin parameter: cosmological simulations and SDSS galaxies compared

TL;DR

This study analyzes the relationship between the galactic spin parameter and galaxy environment and mass using SDSS data and cosmological simulations, revealing a mass-dependent trend not predicted by simulations.

Contribution

It provides the first empirical evidence of a mass dependence of the spin parameter in galaxies, challenging existing simulation predictions.

Findings

No significant dependence of spin on environment.

Low mass galaxies have higher average spin values.

Results challenge current cosmological simulation models.

Abstract

We use a sample of galaxies from the Sloan Digital Sky Survey (SDSS) to search for correlations between the $\lambda$ spin parameter and the environment and mass of galaxies. In order to calculate the total value of $\lambda$ for each observed galaxy, we employed a simple model of the dynamical structure of the galaxies which allows a rough estimate of the value of $\lambda$ using only readily obtainable observables from the luminous galaxies. Use of a large volume limited sample (upwards of 11,000) allows reliable inferences of mean values and dispersions of $\lambda$ distributions. We find, in agreement with some N-body cosmological simulations, no significant dependence of $\lambda$ on the environmental density of the galaxies. For the case of mass, our results show a marked correlation with $\lambda$, in the sense that low mass galaxies present both higher mean values of $\lambda$ and associated dispersions, than high mass galaxies. This last direct empirical result, at odds with expectations from N-body cosmological simulations, provides interesting constrain on the mechanisms of galaxy formation and acquisition of angular momentum, a valuable test for cosmological models.