CANDELS Sheds Light on the Environmental Quenching of Low-mass Galaxies

Abstract

We investigate the environmental quenching of galaxies, especially those with stellar masses (M <SUB>*</SUB>) < 10<SUP>9.5</SUP> M <SUB>☉</SUB>, beyond the local universe. Essentially all local low-mass quenched galaxies (QGs) are believed to live close to massive central galaxies, which is a demonstration of environmental quenching. We use CANDELS data to test whether or not such a dwarf QG-massive central galaxy connection exists beyond the local universe. For this purpose, we only need a statistically representative, rather than complete, sample of low-mass galaxies, which enables our study to z ≳ 1.5. For each low-mass galaxy, we measure the projected distance (d <SUB>proj</SUB>) to its nearest massive neighbor (M <SUB>*</SUB> > 10<SUP>10.5</SUP> M <SUB>☉</SUB>) within a redshift range. At a given z and M <SUB>*</SUB>, the environmental quenching effect is considered to be observed if the d <SUB>proj</SUB> distribution of QGs ({d}<SUB>{proj</SUB>}<SUP>Q</SUP>) is significantly skewed toward lower values than that of star-forming galaxies ({d}<SUB>{proj</SUB>}<SUP>{SF</SUP>}). For galaxies with 10<SUP>8</SUP> M <SUB>☉</SUB> < M <SUB>*</SUB> < 10<SUP>10</SUP> M <SUB>☉</SUB>, such a difference between {d}<SUB>{proj</SUB>}<SUP>Q</SUP> and {d}<SUB>{proj</SUB>}<SUP>{SF</SUP>} is detected up to z ∼ 1. Also, about 10% of the quenched galaxies in our sample are located between two and four virial radii (R <SUB>Vir</SUB>) of the massive halos. The median projected distance from low-mass QGs to their massive neighbors, {d}<SUB>{proj</SUB>}<SUP>Q</SUP>/{R}<SUB>{Vir</SUB>}, decreases with satellite M <SUB>*</SUB> at M <SUB>*</SUB> ≲ 10<SUP>9.5</SUP> M <SUB>☉</SUB>, but increases with satellite M <SUB>*</SUB> at M <SUB>*</SUB> ≳ 10<SUP>9.5</SUP> M <SUB>☉</SUB>. This trend suggests a smooth, if any, transition of the quenching timescale around M <SUB>*</SUB> ∼ 10<SUP>9.5</SUP> M <SUB>☉</SUB> at 0.5 < z < 1.0.