quasars: general; quasars: emission lines; Astrophysics - Astrophysics of Galaxies
Abstract :
[en] 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.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Hutsemekers, Damien ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Agis-Gonzalez, Beatriz ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Inter. fondamentales en physique et astrophysique (IFPA)
Marin, F.; Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550, 67000, Strasbourg, France
Sluse, Dominique ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Ramos Almeida, C.; Instituto de Astrofisica de Canarias, Calle Via Lactea, 38205, La Laguna, Tenerife, Spain ; Departamento de Astrofisica, Universidad de La Laguna, 38205, La Laguna, Tenerife, Spain
Acosta Pulido, J.-A.; Instituto de Astrofisica de Canarias, Calle Via Lactea, 38205, La Laguna, Tenerife, Spain ; Departamento de Astrofisica, Universidad de La Laguna, 38205, La Laguna, Tenerife, Spain)
Alexandroff, R. M., Zakamska, N. L., Barth, A. J., et al. 2018, MNRAS, 479, 4936
Antonucci, R. 1993, ARA&A, 31, 473
Antonucci, R. R. J., & Miller, J. S. 1985, ApJ, 297, 621
Batcheldor, D., Robinson, A., Axon, D. J., et al. 2011, ApJ, 738, 90
Bentz, M. C., Denney, K. D., Grier, C. J., et al. 2013, ApJ, 767, 149
Borguet, B., Hutsemékers, D., Letawe, G., Letawe, Y., & Magain, P. 2008, A&A, 478, 321
Capetti, A., Macchetto, F., Axon, D. J., Sparks, W. B., & Boksenberg, A. 1995, ApJ, 452, L87
Chambers, K. C., Magnier, E. A., & Metcalfe, N. 2016,. ArXiv e-prints [arXiv:1612.05560]
Cohen, R. D., Rudy, R. J., Puetter, R. C., Ake, T. B., & Foltz, C. B. 1986, ApJ, 311, 135
Denney, K. D., De Rosa, G., Croxall, K., et al. 2014, ApJ, 796, 134
di Serego Alighieri, S. 1989, in European Southern Observatory Conference and Workshop Proceedings, eds. P. J. Grosbøl, F. Murtagh, & R. H. Warmels, ESO/ST-ECF Data Analysis Workshop, 31, 157
Eisenstein, D. J., Weinberg, D. H., Agol, E., et al. 2011, AJ, 142, 72
Elitzur, M., Ho, L. C., & Trump, J. R. 2014, MNRAS, 438, 3340
Flewelling, H. A., Magnier, E. A., & Chambers, K. C. 2016,. ArXiv e-prints [arXiv:1612.05243]
Fossati, L., Bagnulo, S., Mason, E., & Landi Degl'Innocenti, E. 2007, in The Future of Photometric, Spectrophotometric and Polarimetric Standardization, ed. C. Sterken, ASP Conf. Ser., 364, 503
Gezari, S., Hung, T., Cenko, S. B., et al. 2017, ApJ, 835, 144
Goodrich, R. W. 1989, ApJ, 340, 190
Goosmann, R. W., & Gaskell, C. M. 2007, A&A, 465, 129
Hamilton, T. S., Casertano, S., & Turnshek, D. A. 2008, ApJ, 678, 22
Husemann, B., Urrutia, T., Tremblay, G. R., et al. 2016, A&A, 593, L9
Hutsemékers, D., Agís González, B., Sluse, D., Ramos Almeida, C., & Acosta Pulido, J.-A. 2017, A&A, 604, L3
Hutsemékers, D., Borguet, B., Sluse, D., & Pelgrims, V. 2018, A&A, 620, A68
Kay, L. E. 1994, ApJ, 430, 196
Khachikian, E. Y., & Weedman, D. W. 1971, ApJ, 164, L109
Kishimoto, M., Kay, L. E., Antonucci, R., et al. 2002, ApJ, 565, 155
Kotilainen, J. K., & Ward, M. J. 1994, MNRAS, 266, 953
LaMassa, S. M., Cales, S., Moran, E. C., et al. 2015, ApJ, 800, 144
Lamy, H., & Hutsemékers, D. 1999, The Messenger, 96, 25
MacLeod, C. L., Ross, N. P., Lawrence, A., et al. 2016, MNRAS, 457, 389
MacLeod, C. L., Green, P. J., Anderson, S. F., et al. 2019, ApJ, 874, 8
Marin, F. 2014, MNRAS, 441, 551
Marin, F. 2017, A&A, 607, A40
Marin, F. 2018, A&A, 615, A171
Marin, F., Goosmann, R. W., Gaskell, C. M., Porquet, D., & Dovčiak, M. 2012, A&A, 548, A121
Marin, F., Goosmann, R. W., & Gaskell, C. M. 2015, A&A, 577, A66
McElroy, R. E., Husemann, B., Croom, S. M., et al. 2016, A&A, 593, L8
Patat, F., & Romaniello, M. 2006, PASP, 118, 146
Penston, M. V., & Perez, E. 1984, MNRAS, 211, 33P
Ramos Almeida, C., Levenson, N. A., Alonso-Herrero, A., et al. 2011, ApJ, 731, 92
Ramos Almeida, C., Martínez González, M. J., Asensio Ramos, A., et al. 2016, MNRAS, 461, 1387
Rojas Lobos, P. A., Goosmann, R. W., Marin, F., & Savić, D. 2018, A&A, 611, A39
Ruan, J. J., Anderson, S. F., Cales, S. L., et al. 2016, ApJ, 826, 188
Runnoe, J. C., Cales, S., Ruan, J. J., et al. 2016, MNRAS, 455, 1691
Serkowski, K. 1958, Acta Astron., 8, 135
Serkowski, K. 1962, Adv. Astron. Astrophys., 1, 289
Shappee, B. J., Prieto, J. L., Grupe, D., et al. 2014, ApJ, 788, 48