摘要：NGC 300 is a low-mass disk galaxy in the Sculptor group. In the literature, it has been identified as a pure exponential disk galaxy, as its luminosity profile can be well fit with a single exponential law over many disk scale lengths (Type I). We investigate the stellar luminosity distribution of NGC 300 usingHubbleSpace Telescope archive data, reaching farther and deeper than any other previous studies. Color-magnitude diagrams show a significant population of old red giant branch (RGB) stars in all fields out toR ∼ 19 kpc (32′), as well as younger populations in the inner regions. We construct the density profiles of the young, intermediate-aged, and old stellar populations, and find two clear breaks in the density profiles of the old RGB and intermediate-aged stars: one down bending (Type II) atR ∼ 5.9 kpc, and another up bending (Type III) atR ∼ 8.3 kpc. Moreover, the old RGB stars exhibit a negative radial color gradient with an upward bend atR ∼ 8 kpc, beyond which the stellar populations are uniformly old (>7 Gyr) and metal poor ([Fe/H] = −1.6−0.4+0.2dex). The outer stellar component atR ⪆ 8 kpc is therefore well separated from the inner disk in terms of stellar density and stellar population. While our results cast doubt on the currently established wisdom that NGC 300 is a pure exponential disk galaxy, a more detailed survey should be carried out to identify the outskirts as either a disk or a stellar halo.
关键词：enGalaxy: halogalaxies: individual: NGC 300Galaxy: structuregalaxies: stellar contentgalaxies: spiral
