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 could be well fitted with a single exponential law over many disk scale lengths ( Type I ) .
We investigate the stellar luminosity distribution of NGC 300 using Hubble Space Telescope ( HST ) 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 to R \sim 19 kpc ( 32 \arcmin ) , as well as younger populations in the inner regions .
We construct the density profiles of the young , intermediate-aged , and old stellar populations .
We find two clear breaks in the density profiles of the old RGB and intermediate-aged stars : one down-bending ( Type II ) at R \sim 5.9 kpc , and another up-bending ( Type III ) at R \sim 8.3 kpc .
Moreover , the old RGB stars exhibit a negative radial color gradient with an up-bending at R \sim 8 kpc , beyond which the stellar populations are uniformly old ( > 7 Gyr ) and metal-poor ( [ Fe / H ] = -1.6 ^ { +0.2 } _ { -0.4 } dex ) .
The outer stellar component at R \gtrapprox 8 kpc is , therefore , well separated from the inner disk in terms of the stellar density and stellar populations .
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 .