Bibcode
Hutsemékers, D.; Agís González, B.; Marin, F.; Sluse, D.; Ramos Almeida, C.; Acosta Pulido, J.-A.
Bibliographical reference
Astronomy and Astrophysics, Volume 625, id.A54, 6 pp.
Advertised on:
5
2019
Journal
Citations
50
Refereed citations
41
Description
If the disappearance of the broad emission lines observed in
changing-look quasars originates from the obscuration of the quasar core
by dusty clouds moving in the torus, high linear optical polarization
would be expected in those objects. We then measured the rest-frame
UV-blue linear polarization of a sample of 13 changing-look quasars, 7
of them being in a type 1.9-2 state. For all quasars but one the
polarization degree is lower than 1%. This suggests that the
disappearance of the broad emission lines cannot be attributed to dust
obscuration, and supports the scenario in which changes of look are
caused by a change in the rate of accretion onto the supermassive black
hole. Such low polarization degrees also indicate that these quasars are
seen under inclinations close to the system axis. One type 1.9-2 quasar
in our sample shows a high polarization degree of 6.8%. While this
polarization could be ascribed to obscuration by a moving dusty cloud,
we argue that this is unlikely given the very long time needed for a
cloud from the torus to eclipse the broad emission line region of that
object. We propose that the high polarization is due to the echo of a
past bright phase seen in polar-scattered light. This interpretation
raises the possibility that broad emission lines observed in the
polarized light of some type 2 active galactic nuclei can be echoes of
past type 1 phases and not evidence of hidden broad emission line
regions.
Based on observations made with the William Herschel telescope operated
on the island of La Palma by the Isaac Newton Group of Telescopes in the
Spanish Observatorio del Roque de los Muchachos of the Instituto de
Astrofísica de Canarias and observations made with ESO Very Large
Telescope at the Paranal Observatory under program ID 101.B-0209.
Related projects
Nuclear Activity in Galaxies: a 3D Perspective from the Nucleus to the Outskirts
This project consists of two main research lines. First, the study of quasar-driven outflows in luminous and nearby obscured active galactic nuclei (AGN) and the impact that they have on their massive host galaxies (AGN feedback). To do so, we have obtained Gran Telescopio CANARIAS (GTC) infrared and optical observations with the instruments
Cristina
Ramos Almeida