Observed and predicted Ly-alpha and UV lines for a sample of galaxies at redshifts z<3.7

TL;DR

This study models the UV and Ly-alpha spectra of galaxies at z<3.7 to understand their emission lines, revealing that most galaxies do not have peculiar gas conditions, with some spectra explained by shock-dominated models.

Contribution

It provides detailed spectral modeling of a diverse galaxy sample, including UV line predictions and insights into gas conditions and shock contributions at various redshifts.

Findings

Most galaxies do not show peculiar gas conditions.

High-velocity gas components are associated with low preshock densities.

Some spectra are best explained by shock-dominated models.

Abstract

We explore the origin of the observed Lya and other UV lines from galaxies at z<3.7 by detailed modelling of the spectra. The objects are chosen among those showing a) UV-optical-near-IR lines, b) only UV lines and c) those showing Lya in the UV and a few optical lines. We also present UV line predictions for a sample of galaxies in the 0.0686<z<0.8829 range. The sample of galaxies including Lya observations in their spectra does not show peculiar physical conditions of the emitting gas, nor abnormal element abundances. However, the high velocity (Vs>1000 km/s) component of the emitting gas is accompanied by relatively low preshock densities (n0 ~100-400 cm^-3) leading in some cases to broad forbidden lines. Some spectra are best reproduced by shock dominated models in which the photoionizing source is hidden or absent. Within more than 50 galaxies modelled in this work, only a few spectra from galaxies at z~2.5 correspond to a starburst temperature Ts>10^5 K, similar to that found in galaxies showing some activity.