Demographics of Star-forming Galaxies since $z\sim2.5$. I. The $UVJ$ Diagram in CANDELS

TL;DR

This study analyzes the demographics and evolution of star-forming galaxies from redshift 0.2 to 2.5 using the CANDELS survey, introducing new methods to predict star-formation rates and identify transitional galaxy populations.

Contribution

It introduces a new calibration to predict SSFR from UVJ colors and a novel plotting scheme to visualize galaxy property evolution, enhancing understanding of galaxy quenching and transition phases.

Findings

UVJ colors correlate with SSFR and dust attenuation.

A calibration predicts SSFR with ~0.2 dex accuracy.

Transition galaxies are identified between star-forming and quiescent populations.

Abstract

This is the first in a series of papers examining the demographics of star-forming galaxies at $0.2<z<2.5$ in CANDELS. We study 9,100 galaxies from GOODS-S and UDS having published values of redshifts, masses, star-formation rates (SFRs), and dust attenuation ($A_V$) derived from UV-optical SED fitting. In agreement with previous works, we find that the $UVJ$ colors of a galaxy are closely correlated with its specific star-formation rate (SSFR) and $A_V$. We define rotated $UVJ$ coordinate axes, termed $S_\mathrm{SED}$ and $C_\mathrm{SED}$, that are parallel and perpendicular to the star-forming sequence and derive a quantitative calibration that predicts SSFR from $C_\mathrm{SED}$ with an accuracy of ~0.2 dex. SFRs from UV-optical fitting and from UV+IR values based on Spitzer/MIPS 24 $\mu\mathrm{m}$ agree well overall, but systematic differences of order 0.2 dex exist at high and low redshifts. A novel plotting scheme conveys the evolution of multiple galaxy properties simultaneously, and dust growth, as well as star-formation decline and quenching, exhibit "mass-accelerated evolution" ("downsizing"). A population of transition galaxies below the star-forming main sequence is identified. These objects are located between star-forming and quiescent galaxies in $UVJ$ space and have lower $A_V$ and smaller radii than galaxies on the main sequence. Their properties are consistent with their being in transit between the two regions. The relative numbers of quenched, transition, and star-forming galaxies are given as a function of mass and redshift.