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Astronomy Colloquium

Thursday, September 11, 2014
4:00 AM
411 West Hall

New postdocs: Yuan Li, Abderahmen Zoghbi, Nick Indriolo

Yuan Li : Modeling AGN Feedback in Cool-Core Galaxy Clusters We study the influence of momentum-driven AGN feedback on cool-core clusters using high-resolution adaptive mesh refinement (AMR) simulations. Run-away cooling first happens only in the central 50 pc region while no local instability develops outside the very center of the cluster. The gas is accreted onto the super-massive black hole which powers AGN jets at an increasing rate as the entropy continues to decrease in the core. The ICM first cools into clumps along the propagation direction of the AGN jets. As the jet power increases, gas condensation occurs isotropically, forming spatially extended (up to a few tens kpc) structures that resemble the observed Ha filaments in Perseus and many other cool-core cluster. Jet heating elevates the gas entropy and cooling time, halting clump formation. The cold gas that is not accreted onto the SMBH settles into a rotating disk. The mass cooling rate averaged over 7 Gyr is ~ 30 M_sun/yr, an order of magnitude lower than the classic cooling flow value (which we obtain in runs without the AGN). Owing to its self-regulating mechanism, AGN feedback can successfully balance cooling with a wide range of model parameters. Besides suppressing cooling, our model produces cold structures in early stages (up to ~ 2 Gyr) that are in good agreement with the observations. However, the long-lived massive cold disk is unrealistic, suggesting that additional physical processes are still needed. Nick Indriolo : Molecular Absorption from the Diffuse ISM to Massive Protostars The abundances of various molecules and the relative populations of quantum states within those molecules harbor information about physical conditions in the ISM. In diffuse clouds, species such as H3+, OH+, and H2O+ are closely linked to ionization of H2 and H. I will briefly discuss the results from our Herschel survey of OH+ and H2O+ in sight lines throughout the Galactic disk regarding the cosmic-ray ionization rate. In the warm, dense gas surrounding massive protostars, reactions drive most of the oxygen into CO and H2O. Spectroscopic observations in the near and mid infrared reveal absorption lines from both species arising in quantum states several hundred to several thousand K above ground. Populations in these states are dependent on the density and temperature, and I will present some of our recent observations and results, including data taken during commissioning operations for EXES on board SOFIA. Abdu Zoghbi : TBA