An optical view of extragalactic gamma-ray emitters

TL;DR

This paper uses optical spectroscopy from the Gran Telescopio Canarias to confirm the nature and determine the redshifts of extragalactic gamma-ray sources, mainly blazars, aiding in understanding their physics and cosmic evolution.

Contribution

It presents an extensive campaign of optical spectroscopic observations to identify blazar properties and constrain their redshifts, improving models of gamma-ray emitters and their role in cosmic background light.

Findings

Confirmed blazar nature of several sources

Determined or constrained redshifts for multiple objects

Provided insights into blazar evolution and background light absorption

Abstract

The Fermi Gamma-ray Observatory discovered about a thousand extragalactic sources emitting energy from 100 MeV to 100 GeV. The majority of these sources belong to the class of blazars characterized by a quasi-featureless optical spectrum (BL Lac Objects). This hampers the determination of their redshift and therefore hinders the characterization of this class of objects. To investigate the nature of these sources and to determine their redshift, we are carrying out an extensive campaign using the 10m Gran Telescopio Canarias to obtain high S/N ratio optical spectra. These observations allow us to confirm the blazar nature of the targets, to find new redshifts or to set stringent limits on the redshift based on the minimum equivalent width of specific absorption features that can be measured in the spectrum and are expected from their host galaxy, assuming it is a massive elliptical galaxy. These results are of importance for the multi-frequencies emission models of the blazars, to test their extreme physics, to shed light on their cosmic evolution and abundance in the far Universe. These gamma emitters are also of great importance for the characterization of the extragalactic background light through the absorption by the IR-optical background photons.