We analyze the vertical distribution of the resolved stellar populations in six low-mass ( V _ { max } = 67 - 131 km s ^ { -1 } ) , edge-on , spiral galaxies observed with the Hubble Space Telescope Advanced Camera for Surveys .
In each galaxy we find evidence for an extraplanar stellar component extending up to 15 scale heights ( 3.5 kpc ) above the plane , with a scale height typically twice that of 2-D fits to K _ { s } band 2MASS images .
We analyze the vertical distribution as a function of stellar age by tracking changes in the color-magnitude diagram .
The young stellar component ( \lesssim 10 ^ { 8 } yrs ) is found to have a scale height larger than the young component in the Milky Way , suggesting that stars in these low mass galaxies form in a thicker disk .
We also find that the scale height of a stellar population increases with age , with young main sequence stars , intermediate age asymptotic giant branch stars , and old red giant branch stars having succesively larger scale heights in each galaxy .
This systematic trend indicates that disk heating must play some role in producing the extraplanar stars .
We constrain the rate of disk heating using the observed trend between scale height and stellar age , and find that the observed heating rates are dramatically smaller than in the Milky Way .
The color distributions of the red giant branch stars well above the midplane indicate that the extended stellar components we see are moderately metal-poor , with peak metallicities around [ Fe/H ] = -1 and with little or no metallicity gradient with height .
The lack of metallicity gradient can be explained if a majority of extraplanar RGB stars were formed at early times and are not dominated by a younger heated population .
Our observations suggest that , like the Milky Way , low-mass disk galaxies also have multiple stellar components .
In its structure , mean metallicity and old age , the RGB component in these galaxies seems analagous to the Milky Way thick disk .
However , without additional kinematic & abundance measurements , this association is only circumstantial , particularly in light of the clear existence of some disk heating at intermediate ages .
Finally , we find that the vertical dust distribution has a scale height somewhat larger than that of the main sequence stars .