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We present the results of a MIPS-24um study of the Brightest Cluster Galaxies(BCGs) of 535 high-redshift galaxy clusters. The clusters are drawn from theSpitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS), whicheffectively provides a sample selected on total stellar mass, over 0.2 < z <1.8 within the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey fields.20%, or 106 clusters have spectroscopically confirmed redshifts, and the resthave redshifts estimated from the color of their red sequence. A comparisonwith the public SWIRE images detects 125 individual BCGs at 24um > 100uJy, or23%. The luminosity-limited detection rate of BCGs in similar richness clusters(Ngal> 12) increases rapidly with redshift. Above z ~ 1, an average of ~20\% ofthe sample have 24um-inferred infrared luminosities of LIR > 10^12 Lsun, whilethe fraction below z ~ 1 exhibiting such luminosities is < 1 \%. TheSpitzer-IRAC colors indicate the bulk of the 24um-detected population ispredominantly powered by star formation, with only 7/125 galaxies lying withinthe color region inhabited by Active Galactic Nuclei (AGN). Simple argumentslimit the star-formation activity to several hundred million years and this maytherefore be indicative of the timescale for AGN feedback to halt the starformation. Below redshift z ~ 1 there is not enough star formation tosignificantly contribute to the overall stellar mass of the BCG population, andtherefore BCG growth is likely dominated by dry-mergers. Above z~ 1, however,the inferred star formation would double the stellar mass of the BCGs and iscomparable to the mass assembly predicted by simulations through dry mergers.We cannot yet constrain the process driving the star formation for the overallsample, though a single object studied in detail is consistent with a gas-richmerger.

The Star-Formation History of BCGs to z = 1.8 from the SpARCS/SWIRE Survey: Evidence for significant in-situ star formation at high-redshift