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Register a new userTesting Quasar Unification: Radiative Transfer in Clumpy Winds
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Various unification schemes interpret the complex phenomenology of quasars and luminous active galactic nuclei (AGN) in terms of a simple picture involving a central black hole, an accretion disc and an associated outflow. Here, we continue our tests of this paradigm by comparing quasar spectra to synthetic spectra of biconical disc wind models, produced with our state-of-the-art Monte Carlo radiative transfer code. Previously, we have shown that we could produce synthetic spectra resembling those of observed broad absorption line (BAL) quasars, but only if the X-ray luminosity was limited to $10^{43}$ erg s$^{-1}$. Here, we introduce a simple treatment of clumping, and find that a filling factor of $sim0.01$ moderates the ionization state sufficiently for BAL features to form in the rest-frame UV at more realistic X-ray luminosities. Our fiducial model shows good agreement with AGN X-ray properties and the wind produces strong line emission in, e.g., Ly alpha and CIV 1550AA at low inclinations. At high inclinations, the spectra possess prominent LoBAL features. Despite these successes, we cannot reproduce all emission lines seen in quasar spectra with the correct equivalent-width ratios, and we find an angular dependence of emission-line equivalent width despite the similarities in the observed emission line properties of BAL and non-BAL quasars. Overall, our work suggests that biconical winds can reproduce much of the qualitative behaviour expected from a unified model, but we cannot yet provide quantitative matches with quasar properties at all viewing angles. Whether disc winds can successfully unify quasars is therefore still an open question.
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Accretion disk winds are thought to produce many of the characteristic features seen in the spectra of active galactic nuclei (AGN) and quasi-stellar objects (QSOs). These outflows also represent a natural form of feedback between the central supermassive black hole and its host galaxy. The mechanism for driving this mass loss remains unknown, although radiation pressure mediated by spectral lines is a leading candidate. Here, we calculate the ionization state of, and emergent spectra for, the hydrodynamic simulation of a line-driven disk wind previously presented by Proga & Kallman (2004). To achieve this, we carry out a comprehensive Monte Carlo simulation of the radiative transfer through, and energy exchange within, the predicted outflow. We find that the wind is much more ionized than originally estimated. This is in part because it is much more difficult to shield any wind regions effectively when the outflow itself is allowed to reprocess and redirect ionizing photons. As a result, the calculated spectrum that would be observed from this particular outflow solution would not contain the ultraviolet spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so highly ionized that line-driving would not actually be efficient. This does not necessarily mean that line-driven winds are not viable. However, our work does illustrate that in order to arrive at a self-consistent model of line-driven disk winds in AGN/QSO, it will be critical to include a more detailed treatment of radiative transfer and ionization in the next generation of hydrodynamic simulations.
We study the geometry and the internal structure of the outflowing wind from the accretion disk of a quasar by observing multiple sightlines with the aid of strong gravitational lensing. Using Subaru/HDS, we performed high-resolution ($R$ $sim$ 36,000) spectroscopic observations of images A and B of the gravitationally lensed quasar SDSS J1029+2623 (at $z_{em}$ $sim$ 2.197) whose image separation angle, $theta$ $sim$ 22$^{primeprime}!!$.5, is the largest among those discovered so far. We confirm that the difference in absorption profiles in the images A and B discovered by Misawa et al. (2013) remains unchanged since 2010, implying the difference is not due to time variability of the absorption profiles over the delay between the images, $Delta t$ $sim$ 744 days, but rather due to differences along the sightlines. We also discovered time variation of C IV absorption strength in both images A and B, due to change of ionization condition. If a typical absorbers size is smaller than its distance from the flux source by more than five orders of magnitude, it should be possible to detect sightline variations among images of other smaller separation, galaxy-scale gravitationally lensed quasars.
Since it became publicly available in 2004, the radiative transfer code STOKES has been used to model the spectroscopic, polarimetric, timing and imaging signatures for different astrophysical scenarios. Ten years later, at the release of a new version of the Monte Carlo code, we make a census of the different scientific cases explored with STOKES and review the main results obtained so far.
Radiative feedback (RFB) from stars plays a key role in galaxies, but remains poorly-understood. We explore this using high-resolution, multi-frequency radiation-hydrodynamics (RHD) simulations from the Feedback In Realistic Environments (FIRE) project. We study ultra-faint dwarf through Milky Way mass scales, including H+He photo-ionization; photo-electric, Lyman Werner, Compton, and dust heating; and single+multiple scattering radiation pressure (RP). We compare distinct numerical algorithms: ray-based LEBRON (exact when optically-thin) and moments-based M1 (exact when optically-thick). The most important RFB channels on galaxy scales are photo-ionization heating and single-scattering RP: in all galaxies, most ionizing/far-UV luminosity (~1/2 of lifetime-integrated bolometric) is absorbed. In dwarfs, the most important effect is photo-ionization heating from the UV background suppressing accretion. In MW-mass galaxies, meta-galactic backgrounds have negligible effects; but local photo-ionization and single-scattering RP contribute to regulating the galactic star formation efficiency and lowering central densities. Without some RFB (or other rapid FB), resolved GMCs convert too-efficiently into stars, making galaxies dominated by hyper-dense, bound star clusters. This makes star formation more violent and bursty when SNe explode in these hyper-clustered objects: thus, including RFB smoothes SFHs. These conclusions are robust to RHD methods, but M1 produces somewhat stronger effects. Like in previous FIRE simulations, IR multiple-scattering is rare (negligible in dwarfs, ~10% of RP in massive galaxies): absorption occurs primarily in normal GMCs with A_v~1.
Gravitationally lensed quasars are useful for studying astrophysics and cosmology, and enlarging the sample size of lensed quasars is important for multiple studies. In this work, we develop a lens search algorithm for four-image (quad) lensed quasars based on their time variability. In the development of the lens search algorithm, we constructed a pipeline simulating multi-epoch images of lensed quasars in cadenced surveys, accounting for quasar variabilities, quasar hosts, lens galaxies, and the PSF variation. Applying the simulation pipeline to the Hyper Suprime-Cam (HSC) transient survey, we generated HSC-like difference images of the mock lensed quasars from Oguri & Marshalls lens catalog. We further developed a lens search algorithm that picks out variable objects as lensed quasar candidates based on their spatial extent in the difference images. We tested our lens search algorithm with the mock lensed quasars and variable objects from the HSC transient survey. Using difference images from multiple epochs, our lens search algorithm achieves a high true-positive rate (TPR) of 90.1% and a low false-positive rate (FPR) of 2.3% for the bright quads with wide separation. With a preselection of the number of blobs in the difference image, we obtain a TPR of 97.6% and a FPR of 2.6% for the bright quads with wide separation. Even when difference images are only available in one single epoch, our lens search algorithm can still detect the bright quads with wide separation at high TPR of 97.6% and low FPR of 2.4% in the optimal seeing scenario, and at TPR of $sim94%$ and FPR of $sim5%$ in typical scenarios. Therefore, our lens search algorithm is promising and is applicable to ongoing and upcoming cadenced surveys, particularly the HSC transient survey and the Rubin Observatory Legacy Survey of Space and Time, for finding new lensed quasar systems. [abridged]
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