The Atacama Cosmology Telescope: the stellar content of galaxy clusters
  selected using the Sunyaev-Zel'dovich effect
  We present a first measurement of the stellar mass component of galaxy
clusters selected via the Sunyaev-Zel'dovich (SZ) effect, using 3.6 um and 4.5
um photometry from the Spitzer Space Telescope. Our sample consists of 14
clusters detected by the Atacama Cosmology Telescope (ACT), which span the
redshift range 0.27 < z < 1.07 (median z = 0.50), and have dynamical mass
measurements, accurate to about 30 per cent, with median M500 = 6.9 x 10^{14}
MSun. We measure the 3.6 um and 4.5 um galaxy luminosity functions, finding the
characteristic magnitude (m*) and faint-end slope (alpha) to be similar to
those for IR-selected cluster samples. We perform the first measurements of the
scaling of SZ-observables (Y500 and y0) with both brightest cluster galaxy
(BCG) stellar mass and total cluster stellar mass (M500star). We find a
significant correlation between BCG stellar mass and Y500 (E(z)^{-2/3} DA^2
Y500 ~ M*^{1.2 +/- 0.6}), although we are not able to obtain a strong
constraint on the slope of the relation due to the small sample size.
Additionally, we obtain E(z)^{-2/3} DA^2 Y500 ~ M500star^{1.0 +/- 0.6} for the
scaling with total stellar mass. The mass fraction in stars spans the range
0.006-0.034, with the second ranked cluster in terms of dynamical mass (ACT-CL
J0237-4939) having an unusually low total stellar mass and the lowest stellar
mass fraction. For the five clusters with gas mass measurements available in
the literature, we see no evidence for a shortfall of baryons relative to the
cosmic mean value.
