(Proposal ID) S14A-011

(PI) Koda Jin

(Proposal Title)
 Probing the Initial Mass Function in Extended Ultraviolet (XUV) Disks

(Abstract)
The GALEX UV satellite discovered tantalizing evidence of star formation (SF) 
far beyond the optical edge of galactic disks (i.e. XUV disk). This discovery 
provides a new opportunity for studying SF in the exceedingly low-density 
environment (~1/10 of typical SF density), spurring intense debate on the 
universality of the initial mass function (IMF) in such exceptional 
environments. Our pilot study led to support for the universal IMF at least in 
M83's XUV disk (Koda et al. 2012). We propose an expansion of the pilot study 
by about an order of magnitude, by observing total ~ 10 XUV disks (6 disks in 
S14A) in NA656(Halpha), B, I, and R-band with S-Cam. In conjunction with GALEX 
UV bands, these images will reveal the presence of O stars (Halpha) and O&B 
stars (UV) in stellar clusters -thus, constraining the high-mass end of the 
IMF. These multi-broadband images will enable us to determine the masses of 
the clusters with much improved accuracy (previously, relied only on R). This 
project will not only increase the statistical significance of our previous 
result, but also enable us to analyze the stochastic effect of IMF sampling in 
very low-mass clusters (102-3 Msun) - the regime of ongoing debate. This 
proposal will complete this on-going project with S-Cam.