The Evolution of Star Formation Activity in Cluster Galaxies Over
  $0.15<z<1.5$
  We explore 7.5 billion years of evolution in the star formation activity of
massive ($M_{\star}>10^{10.1}\,M_{\odot}$) cluster galaxies using a sample of
25 clusters over $0.15<z<1$ from the Cluster Lensing And Supernova survey with
Hubble and 11 clusters over $1<z<1.5$ from the IRAC Shallow Cluster Survey.
Galaxy morphologies are determined visually using high-resolution Hubble Space
Telescope images. Using the spectral energy distribution fitting code CIGALE,
we measure star formation rates, stellar masses, and 4000 \AA\ break strengths.
The latter are used to separate quiescent and star-forming galaxies (SFGs).
From $z\sim1.3$ to $z\sim0.2$, the specific star formation rate (sSFR) of
cluster SFGs and quiescent galaxies decreases by factors of three and four,
respectively. Over the same redshift range, the sSFR of the entire cluster
population declines by a factor of 11, from $0.48\pm0.06\;\mathrm{Gyr}^{-1}$ to
$0.043\pm0.009\;\mathrm{Gyr}^{-1}$. This strong overall sSFR evolution is
driven by the growth of the quiescent population over time; the fraction of
quiescent cluster galaxies increases from $28^{+8}_{-19}\%$ to $88^{+5}_{-4}\%$
over $z\sim1.3\rightarrow0.2$. The majority of the growth occurs at
$z\gtrsim0.9$, where the quiescent fraction increases by 0.41. While the sSFR
of the majority of star-forming cluster galaxies is at the level of the field,
a small subset of cluster SFGs have low field-relative star formation activity,
suggestive of long-timescale quenching. The large increase in the fraction of
quiescent galaxies above $z\sim0.9$, coupled with the field-level sSFRs of
cluster SFGs, suggests that higher redshift cluster galaxies are likely being
quenched quickly. Assessing those timescales will require more accurate stellar
population ages and star formation histories.
