Activity and quiescence in galaxies at redshifts 1.4<z<3.5. The role of the starburst temperature

TL;DR

This study models galaxy spectra at high redshifts to understand the roles of starburst temperature, AGN flux, and shock velocity in galaxy activity and quiescence, revealing diverse star formation states.

Contribution

It introduces a comprehensive spectral modeling approach that incorporates photoionization and shocks to distinguish active and quiescent galaxies at high redshifts.

Findings

Two galaxies exhibit intense starburst activity with high temperatures and shock velocities.

Remaining galaxies show quiescent star formation with lower temperatures.

One galaxy likely hosts a Seyfert 2 like AGN.

Abstract

We investigate 'activity' and 'quiescence' in galaxies at relatively high redshifts by modelling the line(and continuum) spectra of each object. The models account consistently for photoionization and shocks. We claim that the starburst effective temperature, the flux from an AGN, and the shock velocity are critical to activity. The results confirm that two sample galaxies show intense starburst activity with temperatures reaching Ts=2x10^5K and shock velocities Vs> 250 km/s, while for the remaining galaxies of our sample the models show quiescent star formation with Ts< 7x10^4K. A Seyfert 2 like AGN is proposed in one galaxy. The O/H relative abundances derived by the detailed modelling of the spectra are nearly solar for all the sample galaxies, in contrast to those obtained by direct methods.