Luc Binette
Instituto de Astronomia, UNAM, México

Abstract
About 1% of observed galaxies show an active nucleus (AGN) where non-thermal emission is superposed to the stellar emission as a result of accretion around a supermassive black hole. Spectroscopy of AGN reveals the presence of emission lines from a hot plasma of temperature ~104 K. In a fraction of AGN, broad recombination lines are present. In most objects, however, narrow forbidden lines are superposed (NLR) that favor much smaller densities. The accepted dominant excitation mechanism is photoionization by the nuclear accretion disk. Traditionally the inferred temperatures are based on the [OIII] 4363Å/5007Å line ratio. However, if we do not know the plasma density where [OIII] is emitted, we cannot properly constrain the temperature since collisional de-excitation might be present. In the current work, we are proposing to use the density sensitive [ArIV] 4711Å/4740Å line ratio.  Although the [ArIV] lines are very weak, the Australian S7 Survey (Thomas & Dopita et al. 2017) was able to detect them in 16 Seyfert 2. After taking into account the inferred NLR densities, we find an average NLR temperature of 13000±703 K, which standard models have difficulty in reproducing.

2024 April 15, 13:30

IA/U.Porto
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