The Evolution of Star Formation Activity in Cluster Galaxies Over $0.15<z<1.5$

Abstract: 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.