Outside-in disk evolution in the LMC

TL;DR

This study provides observational evidence that the star formation in the LMC disk occurred from the outside-in, with younger stars found closer to the center and older stars in the outskirts, challenging traditional inside-out formation models.

Contribution

It presents new evidence of outside-in disk evolution in the LMC, contrasting with the common inside-out formation scenario for galaxy disks.

Findings

Younger stellar populations are found closer to the LMC center.

Outer regions show little or no current star formation.

Star formation ceased earlier in the outer disk regions.

Abstract

From the analysis of the color-magnitude diagrams and color functions of four wide LMC fields located from ~2 to 6 kpc from the kinematic center of the LMC we present evidence that, while the oldest population is coeval in all fields, the age of the youngest component of the dominant stellar population gradually increases with galactocentric distance, from currently active star formation in a field at 2.3 deg, to 100 Myr, 0.8 Gyr, and 1.5 Gyr in fields at 4.0 deg, 5.5 deg, and 7.1 deg, respectively. This outside-in quenching of the star formation in the LMC disk is correlated with the decreasing HI column density (which is < 2x 10^{20} cm^{-2} in the two outermost fields with little or no current star formation. Other work in the literature hints at similar behavior in the stellar populations of irregular galaxies, and in M33. This is observational evidence against the inside-out disk formation scenario in low-mass spirals and irregular galaxies. Alternatively, it could be that the age distribution with radius results from interplay between the evolution with time of the star-forming area of the LMC and the subsequent outward migration of the stars.