Hot Dust Obscured Galaxies represent a significant fraction of the most luminous heavily obscured quasars known in the Universe. A small subset of them, referred to as BHDs, show excess blue emission, thought to arise from scattered light from the highly obscured quasar. Detailed studies of three of these objects (Assef et al. 2016, 2020) using observations of their morphology with the Hubble Space Telescope, of the X-ray emission with the Chandra Space Telescope, of their UV through mid-IR spectra energy distributions and of their UV emission lines led to the conclusion that the blue excess is due to scattered light from the obscured quasar that powers the mid-IR. Specifically, we find that about 1% of the light from the obscured central engine escapes in some direction and is then scattered into our line of sight. The AGN is so luminous that just 1% of its luminosity is enough to completely hide the host galaxy underneath it. Recently, in Assef et al. (2022), we used imaging polarimetric observations with FORS2 at VLT in the R band of one BHD (W0116-0505, z=3.173) to confirm the nature of the blue excess as scattered light and derive properties of the scattering medium. Our preferred model is that the scatterer is a massive outflow wind driven by the quasar detected by Finnerty et al. (2020) and that may carry over 1,000 M_sun/year of gas. In this project, we are obtaining further imaging polarimetric (ImPol) observations of BHDs using FORS2 at VLT. First, we will obtain V and I ImPol observations of W0116–0505 to better constrain the nature of the scattering material. We will also obtain ImPol observations in R of four additional BHDs to evaluate the prevalence of high polarization fractions in these objects, determine whether all can be modeled with the same physical parameters, as well as assess the possible relation with massive gaseous outflows to test a recent proposed scenario for the evolutionary sequence of luminous quasars. The observations are underway as part of an A-ranked proposal in the 2023A and B semesters.
Type of project: Research, actively recruiting new young researchers
Status: Ongoing
Researchers: Roberto Assef
Funding source: FONDECYT Regular, Basal CATA2