Efficiency tests for estimating the gas and stellar population parameters in Type 2 objects

TL;DR

This study evaluates ULySS's effectiveness in estimating stellar population and AGN emission parameters in Type 2 active galaxies through extensive simulations, highlighting conditions for accurate analysis.

Contribution

It introduces a validated method for simultaneous fitting of AGN and stellar components in galaxy spectra using ULySS, with detailed performance assessment.

Findings

ULySS accurately recovers stellar population characteristics at SNR > 20.

Analysis is reliable when SP contributes more than 10% to total flux.

Degeneracies increase with higher AGN continuum fraction.

Abstract

We investigated the efficiency of estimating characteristics of stellar populations (SP) and Active Galactic Nuclei (AGN) emission using ULySS code. To analyse simultaneously AGN and SP components in the integrated spectrum of Type 2 active galaxies, we modelled the featureless continuum (FC) and emission lines, and we used PEGASE.HR stellar population models provided by ULySS. In order to validate the method, we simulated over 7000 integrated spectra of Seyfert 2 galaxies. Spectra were generated using different characteristics of the featureless AGN continuum, signal-to-noise ratio (SNR), spectral ranges, properties of emission lines and single stellar population (SSP) model whose initial mass function (IMF) and abundance pattern is similar to the solar neighbourhood. Simulated spectra were fitted with ULySS to evaluate the ability of the method to extract SP and AGN properties. We found that the analysis with ULySS can efficiently restore the characteristics of SP in spectra of Seyfert 2 AGNs, where signal-to-noise ratio is higher than 20, and where SP contributes with more than 10% to the total flux. Degeneracies between AGN and SP parameters increase with increasing the AGN continuum fraction, which points out the importance of simultaneous fitting of the FC and SP contributions.