Quenching star formation at intermediate redshifts: downsizing of the mass flux density in the green valley

TL;DR

This study investigates the rapid transition of galaxies from star-forming to passive states at intermediate redshifts, revealing a downsizing pattern where massive galaxies quench earlier and the process shifts to smaller galaxies over time.

Contribution

It provides the first detailed measurement of the stellar mass flux density in the green valley at z ~ 0.8, demonstrating a downsizing trend in galaxy quenching.

Findings

Massive galaxies quenched earlier in cosmic history.

The mass flux density from blue to red galaxies decreases over time.

Quenching occurs more rapidly in the past for larger galaxies.

Abstract

The bimodality in galaxy properties has been observed at low and high redshift, with a clear distinction between star-forming galaxies in the blue cloud and passively evolving objects in the red sequence; the absence of galaxies with intermediate properties indicates that the quenching of star formation and subsequent transition between populations must happen rapidly. In this paper, we present a study of over 100 transiting galaxies in the so-called "green valley" at intermediate redshifts (z ~ 0.8). By using very deep spectroscopy with the DEIMOS instrument at the Keck telescope we are able to infer the star formation histories of these objects and measure the stellar mass flux density transiting from the blue cloud to the red sequence when the universe was half its current age. Our results indicate that the process happened more rapidly and for more massive galaxies in the past, suggesting a top-down scenario in which the massive end of the red sequence is forming first. This represent another aspect of downsizing, with the mass flux density moving towards smaller galaxies in recent times.