Revisiting the stellar mass -- angular momentum -- morphology relation: extension to higher bulge fraction, and the effect of bulge type

TL;DR

This study investigates the relationship between stellar specific angular momentum, stellar mass, and bulge-to-total ratio across various galaxy datasets, revealing distinct behaviors for different bulge types and implications for galaxy formation theories.

Contribution

It extends the stellar mass--angular momentum--morphology relation to higher bulge fractions and distinguishes effects of bulge type on galaxy angular momentum.

Findings

The $M_*-j_*$ relation has a slope of approximately 1.03 when including bulge ratio.

Ignoring bulge ratio, the relation's exponent aligns with dark matter halo predictions (~2/3).

Pseudobulge galaxies follow a different trend than classical bulge galaxies in angular momentum relations.

Abstract

We present the relation between stellar specific angular momentum $j_*$, stellar mass $M_*$, and bulge-to-total light ratio $\beta$ for THINGS, CALIFA and Romanowsky \& Fall datasets, exploring the existence of a fundamental plane between these parameters as first suggested by Obreschkow \& Glazebrook. Our best-fit $M_*-j_*$ relation yields a slope of $\alpha = 1.03 \pm 0.11$ with a trivariate fit including $\beta$. When ignoring the effect of $\beta$, the exponent $\alpha = 0.56 \pm 0.06$ is consistent with $\alpha = 2/3$ predicted for dark matter halos. There is a linear $\beta - j_*/M_*$ relation for $\beta \lesssim 0.4$, exhibiting a general trend of increasing $\beta$ with decreasing $j_*/M_*$. Galaxies with $\beta \gtrsim 0.4$ have higher $j_*$ than predicted by the relation. Pseudobulge galaxies have preferentially lower $\beta$ for a given $j_*/M_*$ than galaxies that contain classical bulges. Pseudobulge galaxies follow a well-defined track in $\beta - j_*/M_*$ space, consistent with Obreschkow \& Glazebrook, while galaxies with classical bulges do not. These results are consistent with the hypothesis that while growth in either bulge type is linked to a decrease in $j_*/M_*$, the mechanisms that build pseudobulges seem to be less efficient at increasing bulge mass per decrease in specific angular momentum than those that build classical bulges.