Stellar populations across the NGC4244 truncated galactic disk

TL;DR

This study uses HST/ACS imaging to analyze stellar populations across the disk of NGC4244, revealing that the disk truncation occurs at the same radius for all ages and is likely caused by dynamical processes rather than star formation thresholds.

Contribution

It provides the first detailed analysis of stellar populations across the truncation in NGC4244, suggesting a dynamical origin for the disk truncation.

Findings

The disk truncation occurs at the same radius for all stellar ages.

The stellar density drops sharply beyond the truncation radius.

The truncation is likely caused by dynamical processes rather than star formation thresholds.

Abstract

We use HST/ACS to study the resolved stellar populations of the nearby, nearly edge-on galaxy NGC4244 across its outer disk surface density break. The stellar photometry allows us to study the distribution of different stellar populations and reach very low equivalent surface brightnesses. We find that the break occurs at the same radius for young, intermediate age, and old stars. The stellar density beyond the break drops sharply by a factor of at least 600 in 5 kpc. The break occurs at the same radius independent of height above the disk, but is sharpest in the midplane and nearly disappears at large heights. These results make it unlikely that truncations are caused by a star formation threshold alone: the threshold would have to keep the same radial position from less than 100 Myr to 10 Gyr ago, in spite of potential disturbances such as infall and redistribution of gas by internal processes. A dynamical interpretation of truncation formation is more likely such as due to angular momentum redistribution by bars or density waves, or heating and stripping of stars caused by the bombardment of dark matter sub-halos. The latter explanation is also in quantitative agreement with the small diffuse component we see around the galaxy.