Mid-Infrared Observations of the Torus of Active Galactic Nuclei

University Of Texas At San Antonio, San Antonio TX

Investigators

Abstract

A fundamental question in astrophysics is how black holes in active galactic nuclei (AGN) are fueled, because black hole fueling affects how galaxies are formed and evolve. The AGN themselves, lying at the very center of the galaxies, are explained as having a torus of gas and dust that blocks light from the inside, and can obscure the AGN central engine (the black hole). However, astronomers don't fully understand the exact properties of the torus, and directly viewing the torus with telescopes is extremely difficult. In this proposal, the PI plans to address the key questions of: (a) What material makes up the torus, and how is it connected to the rest of the gas and dust between the stars of the host galaxy? (b) How do the torus properties, such as geometry and thickness, depend on the brightness of the AGN? (c) Do the properties of the dust in the torus change with the AGN brightness? and (d) What is the role of star formation near the AGN in the centers of galaxies in feeding and/or blocking AGN? Answers to these questions will provide insight into how the AGN is fueled by gas in the galaxy and how that might have an impact on the formation of the galaxy itself. Through the PI's network of collaborators, the proposed work will aid in furthering links in astronomy in the developing nation of Mexico, and it promotes involvement of US Spanish-speaking team members, primarily Hispanics, through connections with Spain and Mexico. The PI also plans to work with local high-school teachers to enhance their understanding and teaching of astronomical topics. In this way, he hopes to reach local school children in the San Antonio area, an area of high diversity, providing high quality scientific content, and encouraging the students (including underrepresented minorities) to pursue scientific fields. The intent is to use the interesting astronomical content as a "gateway" to STEM subjects. Observations at mid-infrared (MIR: 7-26 microns) wavelengths are essential, as the torus intercepts a large amount of electromagnetic radiation emitted from near the black hole and re-radiates it in this waveband. MIR facilities such as the 8m Subaru telescope and the Gran Telescope Canarias (GTC) offer the possibility to probe the centers of AGN at MIR wavelengths with high spatial resolution. Models assuming clumpy dust distribution in AGN are making significant progress explaining MIR emission. High-resolution observation will help constrain model parameters and provide insight into torus physical properties. This proposal would fund analysis of data from ~100 hours of guaranteed time (GT) on the GTC and an additional 180 hours of ESO-GTC time (jointly ESO and GTC allocated time, competitively awarded as part of Spain's ascension to ESO membership). This would be combined with archival data from Gemini to tackle a key problem in AGN research. A detailed understanding of the torus, the AGN/black hole fueling process and its relationship to (or even creation of) the torus, the interaction with the host galaxy, and dust chemistry in other galaxies will be constructed. Simulations based on current data to prepare new observations for next generation facilities (such as SOFIA, JWST, TMT, etc.) are planned.