Isolating the young stellar population in the outer disk of NGC 300

TL;DR

This study analyzes the recent star formation history in the outer disk of NGC 300 using Hubble Space Telescope data, revealing an unbroken young stellar disk extending at least 8 scale lengths, indicating an undisturbed, isolated galaxy.

Contribution

It provides the first detailed SFH analysis of NGC 300's outer disk, showing the young stellar disk is unbroken and extends beyond 8 scale lengths, contrasting with disturbed HI morphology.

Findings

Young stellar disk extends unbroken to at least 8 scale lengths.

No correlation between disturbed HI outer disk and young stellar disk.

NGC 300's disk resembles that of isolated galaxies like NGC 2403.

Abstract

The recent star formation history (SFH) in the outer disk of NGC 300 is presented through the analysis of color magnitude diagrams (CMDs). We analyze resolved stellar photometry by creating CMDs from four Hubble Space Telescope fields containing a combination of images from the Advanced Camera for Surveys and the UVIS imager aboard the Wide Field Camera 3. From the best models of these CMDs, we derive the SFH in order to extract the young stellar component for the past 200 Myrs. We find that the young stellar disk of NGC 300 is unbroken out to at least ${\sim}$8 scale lengths (including an upper limit out to ${\sim}$10 scale lengths) with $r{_s}$ = 1.4 ${\pm}$ 0.1 kpc, which is similar to the total stellar surface brightness profile. This unbroken profile suggests that NGC 300 is undisturbed, similar to the isolated disk galaxy NGC 2403. We compare the environments of NGC 300, NGC 2403, and M33 along with the properties of the gas and stellar disks. We find that the disturbed HI outer disk morphology is not accompanied by a break in the young stellar disk. This may indicate that processes which affect the outer HI morphology may not leave an imprint on the young stellar disk.