# KMOS-3D Reveals Low-Level Star Formation Activity in Massive Quiescent Galaxies at 0.7 < z < 2.7

## TL;DR

This study investigates low-level star formation in massive quiescent galaxies at redshifts 0.7 to 2.7, revealing that some exhibit signs of rejuvenation possibly due to inflows or minor mergers, challenging the notion of complete quiescence.

## Contribution

First detailed analysis of H-alpha emission in quiescent galaxies at these redshifts, identifying low-level star formation and its potential fueling mechanisms.

## Key findings

- H-alpha detected in 20/120 galaxies, with 9 showing star formation.
- Star formation rates are low, below the main sequence.
- Many galaxies have close companions and lower metallicity.

## Abstract

We explore the H-alpha emission in the massive quiescent galaxies observed by the KMOS-3D survey at 0.7 < z < 2.7. The H-alpha line is robustly detected in 20 out of 120 UVJ-selected quiescent galaxies, and we classify the emission mechanism using the H-alpha line width and the [NII]/H-alpha line ratio. We find that AGN are likely to be responsible for the line emission in more than half of the cases. We also find robust evidence for star formation activity in nine quiescent galaxies, which we explore in detail. The H-alpha kinematics reveal rotating disks in five of the nine galaxies. The dust-corrected H-alpha star formation rates are low (0.2 - 7 Msun/yr), and place these systems significantly below the main sequence. The 24micron-based infrared luminosities, instead, overestimate the star formation rates. These galaxies present a lower gas-phase metallicity compared to star-forming objects with similar stellar mass, and many of them have close companions. We therefore conclude that the low-level star formation activity in these nine quiescent galaxies is likely to be fueled by inflowing gas or minor mergers, and could be a sign of rejuvenation events.