Oral Presentation

Reconstructing the Initial Conditions from Galaxy Light Sizes

Author(s): Jounghun Lee (Seoul National University)

Presenter: Jounghun Lee (Seoul National University)

We present an observational evidence supporting the scenario that the protogalactic angular momenta play the most decisive role in
molding the luminosity sizes of present galaxies. Analyzing the NASA-Sloan Atlas galaxy catalog, we determine the size distributions of
local galaxies in the redshift range of $0.1\le z\le 0.2$, and find them to be well described by a bimodal Gamma mixture model,
which is consistent with the recent numerical result. Classifying the local galaxies by their ratios, $r_{50}/r_{90}$, where $r_{50}$ and $r_{90}$
denote the galaxy sizes enclosing $50\%$ and $90\%$ of their total luminosities, respectively,
we also find the size distributions of spiral galaxies with $r_{50}/r_{90}\ge 0.45$ to follow a unimodal Gamma model.
Assuming the existence of a linear causal correlation between the present galaxy sizes and the primordial spin factor, $\tau$, defined as the
degree of misalignments between the initial tidal and protogalaxy inertia tensors,
we reconstruct the $\tau$-distributions directly from the observed size distributions of local spiral galaxies, and demonstrate their excellent
agreements with the real $\tau$-distributions determined at the protogalactic stages by the prior numerical experiment.