Redistribution of Stars and Gas in the Star Formation Deserts of Barred Galaxies

TL;DR

This study investigates the star formation deserts in barred galaxies, revealing that star age distributions are influenced more by stellar migration than by immediate effects of bar formation, complicating age-based dating of bar epochs.

Contribution

It demonstrates that star age distributions in star formation deserts are affected by stellar migration, challenging previous assumptions about using these regions to date bar formation.

Findings

Old stars dominate the SFD regions with few younger than 10 Myr.

Gas removal in SFDs occurs within 1 Gyr after bar formation.

Star age distribution shows a gradual downturn, not a sharp truncation, due to stellar migration.

Abstract

Bars strongly influence the distribution of gas and stars within the central regions of their host galaxies. This is particularly pronounced in the star formation desert (SFD) which is defined as two symmetrical regions either side of the bar that show a deficit in young stars. Previous studies proposed that, if star formation is truncated because of the influence of the bar, then the age distribution of stars within the SFD could be used to determine the epoch of bar formation. To test this, we study the properties of SFDs in 6 galaxies from zoom-in cosmological re-simulations. Age maps reveal old regions on both sides of the bars, with a lack of stars younger than 10 Myr, confirming the SFD phenomenon. Local star formation is truncated in the SFDs because after the bar forms, gas in these regions is removed on 1 Gyr timescales. However, the overall age distribution of stars in the SFD does not show a sharp truncation after bar formation but rather a gradual downturn in comparison to that of the bar. This more subtle signature may still give information on bar formation epochs in observed galaxies, but the interpretation will be more difficult than originally hoped. The gradual drop in the SFD age distribution, instead of a truncation, is due to radial migration of stars born in the disk. The SFD is thus one of the only regions where an uncontaminated sample of stars only affected by radial migration can be studied.