Imaging Polarization of the Blue-excess Hot Dust-obscured Galaxy WISE J011601.41–050504.0
We report on VLT/FORS2 imaging polarimetry observations in the R_(Special) band of WISE J011601.41–050504.0 (W0116–0505), a heavily obscured hyperluminous quasar at z = 3.173 classified as a Hot Dust-obscured Galaxy (Hot DOG) based on its mid-IR colors. Recently, Assef et al. identified W0116–0505 as having excess rest-frame optical/UV emission and concluded that this excess emission is most likely scattered light from the heavily obscured AGN. We find that the broadband rest-frame UV flux is strongly linearly polarized (10.8% ± 1.9%, with a polarization angle of 74° ± 9°), confirming this conclusion. We analyze these observations in the context of a simple model based on scattering either by free electrons or by optically thin dust, assuming a classical dust torus with polar openings. Both can replicate the degree of polarization and the luminosity of the scattered component for a range of geometries and column densities, but we argue that optically thin dust in the ISM is the more likely scenario. We also explore the possibility that the scattering medium corresponds to an outflow recently identified for W0116–0505. This is a feasible option if the outflow component is biconical with most of the scattering occurring at the base of the receding outflow. In this scenario, the quasar would still be obscured even if viewed face-on but might appear as a reddened type 1 quasar once the outflow has expanded. We discuss a possible connection between blue-excess Hot DOGs, extremely red quasars, reddened type 1 quasars, and unreddened quasars that depends on a combination of evolution and viewing geometry.
© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 February 18; revised 2022 May 26; accepted 2022 June 11; published 2022 July 28. We thank Aleksandar Cikota for helping us with the reduction of the FORS2 imaging polarimetry data and Matthew Temple and Aaron Barth for comments and suggestions that helped improve our work. We also thank the anonymous referee for all of the comments and suggestions on the submitted manuscript. R.J.A. was supported by FONDECYT grant No. 1191124 and ANID BASAL project FB210003. F.E.B. acknowledges support from ANID-Chile BASAL AFB-170002, ACE210002, and FB210003; FONDECYT Regular 1200495 and 1190818; and Millennium Science Initiative Program ICN12_009. H.D.J. was supported by National Research Foundation of Korea (NRF) grant 2022R1C1C2013543 funded by the Ministry of Science and ICT (MSIT) of Korea. C.W.T. acknowledges support from NSFC grant 11973051. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 106.218J.001. This research uses data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory (JPL)/California Institute of Technology (Caltech), funded by the National Aeronautics and Space Administration (NASA). Portions of this research were carried out at JPL/Caltech under a contract with NASA. This research made use of Photutils, an Astropy package for detection and photometry of astronomical sources (Bradley et al. 2019). This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 526555. These observations are associated with program 14358. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science.
Accepted Version - 2206.04093.pdf
Published - Assef_2022_ApJ_934_101.pdf