Quenching and the UVJ diagram in the SIMBA cosmological simulation

Over the past decade, rest-frame color-color diagrams have become popular tools for selecting quiescent galaxies at high redshift, breaking the color degeneracy between quiescent and dust-reddened star-forming galaxies. In this work, we study one such color-color selection tool — the rest-frame U−V vs. V−J diagram — by employing mock observations of cosmological galaxy formation simulations. In particular, we conduct numerical experiments assessing both trends in galaxy properties in UVJ space as well as the color-color evolution of massive galaxies as they quench at redshifts z∼1−2. We find that our models broadly reproduce the observed UVJ diagram at z=1−2; however, our models do not produce a clear bimodality in UVJ space, largely due to the overpopulation of the green valley in SIMBA. We predict increasing AV as galaxies move toward redder U−V and V−J colors, with attenuation curves becoming flatter (greyer) with increasing mass. This latter trend results in both relatively muted trends between inferred sSFRs and U−V and V−J colors, as well as a lack of the reddest colors in our most massive systems. When investigating the time evolution of galaxies on the UVJ diagram, we find that the quenching pathway on the UVJ diagram is independent of the quenching timescale, and instead dependent primarily on the average sSFR in the 1 Gyr prior to the onset of quenching. Our results support the interpretation of different quenching pathways as corresponding to the divergent evolution of post-starburst and green valley galaxies.

Quenching and the UVJ diagram in the SIMBA cosmological simulation, Hollis B. AkinsDesika NarayananKatherine E. WhitakerRomeel DavéSidney LowerRachel BezansonRobert FeldmannMariska Kriek, arXiv:2105.12748, Submitted to ApJ