1. Determining star formation rates in active galactic nuclei hosts via stellar population synthesis
- Author
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Nicholas Fraser Boardman, Nícolas Dullius Mallmann, Sandro Barboza Rembold, Luiz N. da Costa, D. V. Bizyaev, Médéric Boquien, J. S. Schimoia, Rogério Riffel, Guilherme S. Couto, Thaisa Storchi-Bergmann, Gabriele da Silva Ilha, Rogemar A. Riffel, and Janaina Correa do Nascimento
- Subjects
Physics ,Active galactic nucleus ,Stellar population ,Star formation ,Extinction (astronomy) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Older population ,Stars ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Emission spectrum ,Astrophysics::Galaxy Astrophysics - Abstract
The effect of active galactic nuclei (AGN) feedback on the host galaxy, and its role in quenching or enhancing star-formation, is still uncertain due to the fact that usual star-formation rate (SFR) indicators -- emission-line luminosities based on the assumption of photoionisation by young stars -- cannot be used for active galaxies as the ionising source is the AGN. We thus investigate the use of SFR derived from the stellar population and its relation with that derived from the gas for a sample of 170 AGN hosts and a matched control sample of 291 galaxies. We compare the values of SFR densities obtained via the Ha emission line (SFRg) for regions ionised by hot stars according to diagnostic diagrams with those obtained from stellar population synthesis (SFRstars) over the last 1 to 100~Myr. We find that the SFRstars over the last 20~Myrs closely reproduces the SFRg, although a better match is obtained via the transformation: log(SFRstars) = (0.872+/-0.004) log(SFRg) -(0.075+/-0.006), which is valid for both AGN hosts and non-active galaxies. We also compare the reddening obtained via the gas Ha/Hb ratio with that derived via the full spectral fitting in the stellar population synthesis. We find that the ratio between the gas and stellar extinction is in the range 2.64 < A_Vgas/A_Vstar} < 2.85, in approximate agreement with previous results from the literature, obtained for smaller samples. We interpret the difference as being due to the fact that the reddening of the stars is dominated by that affecting the less obscured underlying older population, while the reddening of the gas is larger as it is associated to a younger stellar population buried deeper in the dust., 13 pages, accepted for publication in MNRAS
- Published
- 2020