The young nuclear stellar disc in the SB0 galaxy NGC 1023

TL;DR

This study investigates the nuclear stellar disc in NGC 1023, revealing it is younger and more metal-rich than the bulge, supporting a star formation origin from enriched gas rather than star cluster migration.

Contribution

It provides new evidence that the nuclear disc formed from gas accretion and star formation, not from dissipationless star cluster migration, in an interacting SB0 galaxy.

Findings

Nuclear disc stars are younger and more metal-rich than bulge stars.

Star formation from enriched gas is the likely origin of the nuclear disc.

Dissipationless formation from star cluster migration is rejected.

Abstract

Small kinematically-decoupled stellar discs with scalelengths of a few tens of parsec are known to reside in the centre of galaxies. Different mechanisms have been proposed to explain how they form, including gas dissipation and merging of globular clusters. Using archival Hubble Space Telescope imaging and ground-based integral-field spectroscopy, we investigated the structure and stellar populations of the nuclear stellar disc hosted in the interacting SB0 galaxy NGC 1023. The stars of the nuclear disc are remarkably younger and more metal rich with respect to the host bulge. These findings support a scenario in which the nuclear disc is the end result of star formation in metal enriched gas piled up in the galaxy centre. The gas can be of either internal or external origin, i.e. from either the main disc of NGC 1023 or the nearby satellite galaxy NGC 1023A. The dissipationless formation of the nuclear disc from already formed stars, through the migration and accretion of star clusters into the galactic centre is rejected.