October 24-28, 2016

Abstract

Dust in the wind: the mineralogy of newly formed dust in Active Galactic Nuclei

Sundar Srinivasan (ASIAA)

Ciska Kemper (ASIAA) Lei Hao (Shanghai Astronomical Observatory) Peter Scicluna (ASIAA) Yanxia Xie (Kavli Institute for Astronomy and Astrophysics, Peking University) Sarah Gallagher (Department of Physics and Astronomy, University of Western Ontario) Luis Ho (Kavli Institute for Astronomy and Astrophysics, Peking University)

The origin of large reservoirs of dust (Priddey et al. 2003; Beelen et al. 2006)  in the early universe still remains a mystery. The traditional (stellar) dust sources are not sufficiently productive during the first Gyr to explain the reservoir observed (Morgan & Edmunds 2003; Rowlands et al. 2014), and, furthermore, the extinction curves at high redshift are markedly different from those observed in the local universe (Maiolino et al. 2004; Stratta et al. 2007). Therefore, additional dust sources have been invoked, such as interstellar grain formation and grain growth (Martini et al. 2013). Additionally, by comparison with the dust forming environments around evolved low mass stars, Elvis et al. (2002) argue that the conditions in winds launched from the accretion discs of Active Galactic Nuclei (AGN) accretion disks allow for the formation of significant quantities of dust. This dust source would not only help resolve the so-called dust budget crisis at high redshift, but also provides a natural explanation for the origin of the dusty AGN torus (Elitzur & Shlosman 2006). We have selected a sample of Palomar Green (PG) quasars with Herschel and AKARI photometry from the sample of Petric et al. (2015), and required their archival Spitzer spectra to show the 9.7 micron silicate feature in emission. The Herschel photometry will constrain the far-infrared continuum. We will chart the variety in mineralogy present in quasar winds, and compare the results with other work present in the literature (e.g. Köhler & Li 2010; Smith et al. 2010; Xie et al. 2014), studies which have all targeted single objects, or very small samples. From spectral fitting of the solid state features seen towards these objects in the 5-40 μm wavelength range, using the method described by Markwick-Kemper et al. (2007), we can identify the dust composition in the disk wind and torus, including amorphous and crystalline silicates, as well as more primitive condensates, such as alumina (Al2O3) and periclase (MgO). Thus, future studies using the MIRI mid-infrared spectroscopy mode, potentially provide a systematic probe for the conditions in the dust condensation zone in quasar winds.

Mode of presentation: poster