Forming Lenticular Galaxies via Violent Disk Instability

TL;DR

This paper proposes a novel mechanism for forming lenticular galaxies through violent disk instability in isolated galaxies, leading to bulge growth and disk heating, matching observed S0 properties without requiring environmental interactions.

Contribution

It introduces a new formation pathway for S0 galaxies via internal disk instability, independent of mergers or dense environments.

Findings

Galaxies become violently unstable, fragment, and form stellar clumps.

Bulge growth and disk heating occur within less than a billion years.

Resulting models resemble observed S0 galaxies in morphology and kinematics.

Abstract

Lenticular galaxies are generally thought to have descended from spirals via morphological transformation, although recent numerical simulations have shown that minor or even major merger can also lead to an S0-like remnant. These mechanisms, however, are active in a dense environment such as a group or a cluster of galaxies - making it harder to explain the remarkable fraction of S0s found in the field. Here, we propose a new mechanism to form such lenticular galaxies. We show that an isolated cold disk settled into rotational equilibrium becomes violently unstable - leading to fragmentation and formation of stellar clumps that, in turn, not only grow the bulge, but also increase the stellar disk velocity dispersion optimally in less than a billion year. Subsequently, the galaxy evolves passively without any conspicuous spiral structure. The final galaxy models resemble remarkably well the morphology and stellar kinematics of the present-day S0s observed by the Planetary Nebulae spectrograph. Our findings suggest a natural link between the high-redshift clumpy progenitors to the present-day S0 galaxies.