Where are the Broad Absorption Line Outflows Situated and How Important are they to Active Galactic Nuclei Feedback?

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Quasars are the most luminous objects in the universe. The active galactic nucleus (AGN) that is the quasar's powerhouse can outshine its entire host galaxy. In the more than fifty years since their discovery, a picture has emerged of a quasar as a supermassive black hole residing at or near the center of a large galaxy. Interstellar gas in the galaxy, perhaps the residue of stars disrupted by tidal forces as they orbit close to the black hole, falls into the black hole and in doing so is heated to very high temperatures and emits copious radiation over a wide range of wavelengths. Along with the gas inflow, it is also clear that quasars drive gas out of the nuclear region. This is evidenced by jets of material emitted by a minority of quasars but also by an outflow seen in absorption in the spectra of many quasars. These objects are called broad absorption line quasars or BAL quasars in reference to the broad spectral features due to mildly-ionized atomic species seen in their ultraviolet spectra. Long thought to be oddities, it is becoming clear that many or most quasars demonstrate such spectral features when viewed along certain lines of sight. An outstanding question is how the BAL outflow is generated. Is it gas that is launched from very near the black hole or is its genesis from somewhere outside of the nuclear region? The answer is important because, depending on its strength, the BAL wind can affect the properties of the host galaxy through so-called quasar feedback. This project will use detailed spectral analysis and imaging of a number of BAL quasars to better determine where the BAL gas originates and what its properties are. The project will engage a number of undergraduate researchers many of whom are women or underrepresented minorities. Arguably the most important parameter to be determined for broad absorption line outflows is their distance from the central source (R). A definitive answer will go a long way to: (a) determine whether these outflows are energetic enough to generate the sought after "quasar mode feedback," which is suggested by theorists to be a key mechanism for influencing the assembly history of galaxies and clusters; (b) establish the role of the outflows in the connection between the supermassive black hole and the host galaxy; (c) allow for realistic modeling of the outflow's origin and acceleration. Most AGN researchers and especially dynamical modelers, favor a picture where BAL outflows are launched from the AGN accretion disc and are observed in its vicinity (R~0.01-0.1 pc). However, in a recent series of papers the principal investigator's team measured R to more than 20 outflow components in 10 individual quasars and in every case found R to be between 100-10,000 parsecs. The large difference between the previously assumed and measured R has dramatic consequences since the outflow's mass flux and kinetic luminosity are linearly dependent on R. A prominent result was the team's finding of the most energetic quasar outflow measured to date, with ample kinetic luminosity to be a major contributor to AGN feedback. Therefore, if these large R flows are representative of most BAL outflows, they can supply the theoretically desired quasar mode feedback. This project will advance this unique observational and modeling program by observing a heterogeneous set of objects, to analyzing samples in well-designed surveys, acquiring direct imaging spectroscopy of these outflows, and extracting R from rich new data sets of BAL variability. The result should definitively assess whether BAL winds can be a dominant agent of AGN feedback.