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We analyze the vertical distribution of the resolved stellar populations insix low-mass, edge-on, spiral galaxies observed with the Hubble Space TelescopeAdvanced Camera for Surveys. In each galaxy we find evidence for an extraplanarstellar component extending up to 15 scale heights (3.5 kpc) above the plane.We analyze the vertical distribution as a function of stellar age by trackingchanges in the color-magnitude diagram. The young stellar component (<10^8 yrs)is found to have a scale height larger than the young component in the MilkyWay, 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 eachgalaxy. This systematic trend indicates that disk heating must play some rolein producing the extraplanar stars. We constrain the rate of disk heating usingthe observed trend between scale height and stellar age, and find that theobserved heating rates are dramatically smaller than in the Milky Way. Thecolor distributions of the red giant branch stars well above the midplaneindicate that the extended stellar components we see are moderately metal-poor,with peak metallicities around [Fe/H]=-1 and with little or no metallicitygradient with height. The lack of metallicity gradient can be explained if amajority of extraplanar RGB stars were formed at early times and are notdominated by a younger heated population. Our observations suggest that, likethe Milky Way, low-mass disk galaxies also have multiple stellar components. Inits structure, mean metallicity and old age, the RGB component in thesegalaxies seems analagous to the Milky Way thick disk. [ABRIDGED]

the astronomical journal

A Study of Edge-On Galaxies with the<i>Hubble Space Telescope</i>Advanced Camera for Surveys. II. Vertical Distribution of the Resolved Stellar Population

A Study of Edge-On Galaxies with theHubble Space TelescopeAdvanced Camera for Surveys. II. Vertical Distribution of the Resolved Stellar Population