Dependence of Galaxy Stellar Properties on the Primordial Spin Factor

TL;DR

This study reveals that primordial spin factors influence present galaxy stellar properties, with stronger effects observed in higher mass galaxies, highlighting the importance of initial conditions in galaxy evolution.

Contribution

It introduces a novel analysis linking primordial density and tidal fields to galaxy properties using Shannon's information theory on simulation data.

Findings

Significant mutual information between primordial spin factor and galaxy properties in high-mass galaxies.

Galaxy sizes are most robustly dependent on the primordial spin factor, following a bimodal Gamma distribution.

Galaxies from higher primordial spin sites tend to be larger, younger, and bluer.

Abstract

We present a numerical discovery that the observable stellar properties of present galaxies retain significant dependences on the primordial density and tidal fields. Analyzing the galaxy catalogs from the TNG300-1 simulations, we first compute the primordial spin factor, $\tau$, defined as the mean degree of misalignments between the principal axes of the initial density and potential hessian tensors at the protogalactic sites. Then, we explore in the framework of Shannon's information theory if and how strongly each of six stellar properties of the present galaxies, namely two stellar sizes ($R_{90\star}$ and $R_{50\star}$), ages, specific star formation rates, optical colors and metallicities, share mutual information with $\tau$, measured at $z=127$. Deliberately controlling the TNG galaxy samples to have no differences in the mass, environmental density and shear distributions, we single out net effects of $\tau$ on each of the galaxy stellar properties. In the higher stellar mass range of $M_{\star}/(h^{-1}\,M_{\odot})\ge 10^{10}$, significant amounts of mutual information with $\tau$ are exhibited by all of the six stellar properties, while in the lower range of $M_{\star}/(h^{-1}\,M_{\odot})< 10^{10}$ only four of the six properties except for the specific star formation rates and colors yield significant signals of $\tau$-dependence. Examining how the mean values of the six stellar properties vary with $\tau$, we also show that the galaxies originated from the protogalactic sites with higher $\tau$ values tend to have larger sizes, later formation epochs, higher specific star formation rates, bluer colors and lower metallicities. It is also discovered that the galaxy stellar sizes, which turn out to be most robustly dependent on $\tau$ regardless of $M_{\star}$, follow a bimodal Gamma distribution, the physical implication of which is discussed.