S0 galaxies are faded spirals: clues from their angular momentum content

TL;DR

This study investigates the angular momentum of S0 galaxies, revealing most have similar properties to spirals, implying they likely evolve from spirals through secular processes rather than mergers.

Contribution

The paper provides the first detailed analysis of the angular momentum content of S0 galaxy discs, linking their formation to spiral galaxy fading rather than mergers.

Findings

Most S0 discs have angular momentum similar to spiral discs.

Two S0s with low angular momentum show signs of recent mergers.

Secular evolution and fading are primary in S0 formation in low-density environments.

Abstract

The distribution of galaxies in the stellar specific angular momentum versus stellar mass plane ($j_{\star}$-$M_{\star}$) provides key insights into their formation mechanisms. In this paper, we determine the location in this plane of a sample of ten field/group unbarred lenticular (S0) galaxies from the CALIFA survey. We performed a bulge-disc decomposition both photometrically and kinematically to study the stellar specific angular momentum of the disc components alone and understand the evolutionary links between S0s and other Hubble types. We found that eight of our S0 discs have a distribution in the $j_{\star}$-$M_{\star}$ plane that is fully compatible with that of spiral discs, while only two have values of $j_{\star}$ lower than the spirals. These two outliers show signs of recent merging. Our results suggest that merger and interaction processes are not the dominant mechanisms in S0 formation in low-density environments. Instead, S0s appear to be the result of secular processes and the fading of spiral galaxies after the shutdown of star formation.