The origin of the LMC stellar bar: clues from the SFH of the bar and inner disk

TL;DR

This study compares star formation histories in the LMC's bar and inner disk, suggesting the bar formed from disk material redistribution during disk instability, not from a distinct star formation event.

Contribution

It provides evidence that the LMC stellar bar likely formed through disk instability and shared a common SFH with the inner disk, challenging classic buckling formation scenarios.

Findings

SFHs are consistent across bar and inner disk fields.

No specific star formation event correlates with bar formation.

SFH uniformity rules out significant spatial variations across the bar.

Abstract

We discuss the origin of the LMC stellar bar by comparing the star formation histories (SFH) obtained from deep color-magnitude diagrams (CMDs) in the bar and in a number of fields in different directions within the inner disk. The CMDs, reaching the oldest main sequence turnoffs in these very crowded fields, have been obtained with VIMOS on the VLT in service mode, under very good seeing conditions. We show that the SFHs of all fields share the same patterns, with consistent variations of the star formation rate as a function of time in all of them. We therefore conclude that no specific event of star formation can be identified with the formation of the LMC bar, which instead likely formed from a redistribution of disk material that occurred when the LMC disk became bar unstable, and shared a common SFH with the inner disk thereafter. The strong similarity between the SFH of the center and edge of the bar rules out significant spatial variations of the SFH across the bar, which are predicted by scenarios of classic bar formation through buckling mechanisms.