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The host galaxies of luminous type 2 AGNs at z ∼ 0.3-0.4

J. J. Urbano-Mayorgas, M. Villar-Martín, F. Buitrago, J. Piqueras-Lopez, B. Rodriguez del Pino, A. M. Koekemoer, M. Huertas-Company, C. N. Tadhunter

Abstract

We study the morphological and structural properties of the host galaxies associated with 57 optically selected luminous type 2 active galactic nuclei (AGNs) at z ∼ 0.3–0.4: 16 high-luminosity Seyfert 2 [HLSy2, 8.0 ≤ log(⁠L[OIII]/L⊙)< 8.3] and 41 obscured [QSO2, log(⁠L[OIII]/L⊙)≥ 8.3] quasars. With this work, the total number of QSO2s at z < 1 with parametrized galaxies increases from ∼35 to 76. Our analysis is based on Hubble Space Telescope WFPC2 and ACS images that we fit with galfit. HLSy2s and QSO2s show a wide diversity of galaxy hosts. The main difference lies in the higher incidence of highly disturbed systems among QSO2s. This is consistent with a scenario in which galaxy interactions are the dominant mechanism triggering nuclear activity at the highest AGN power. There is a strong dependence of galaxy properties with AGN power (assuming L[OIII] is an adequate proxy). The relative contribution of the spheroidal component to the total galaxy light (B/T) increases with L[OIII]⁠. While systems dominated by the spheroidal component spread across the total range of L[OIII]⁠, most disc-dominated galaxies concentrate at log(⁠L[OIII]/L⊙)<8.6. This is expected if more powerful AGNs are powered by more massive black holes which are hosted by more massive bulges or spheroids. The average galaxy sizes (〈re〉) are 5.0 ± 1.5 kpc for HLSy2s and 3.9 ± 0.6 kpc for HLSy2s and QSO2s, respectively. These are significantly smaller than those found for QSO1s and narrow-line radio galaxies at similar z⁠. We put the results of our work in the context of related studies of AGNs with quasar-like luminosities.

Keywords
galaxies: active; galaxies: evolution; quasars: general

Monthly Notices of the Royal Astronomical Society
Volume 483, Issue 2, Page 1829
2019 February

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia