Research Note

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

¹ Dipartimento di Fisica e AstronomiaUniversity of Padova, Vicolo dell’Osservatorio 2, 35133 Padova, Italy
e-mail: contini@post.tau.ac.il
² School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv, Israel

Received: 9 April 2014
Accepted: 7 October 2014

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 T_∗ = 2 × 10⁵ K and shock velocities V_s> 250 km s^-1, while for the remaining galaxies in our sample, the models show quiescent star formation with T_∗ ≤ 7 × 10⁴ K. 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.