List of Past CTC Theory Lunches : 01-Sep-2018 to 31-Dec-2018

Date:   Monday 12-Nov-2018
Speaker:   Matej Malik
Title:  "Radiative Transfer Modeling of Exoplanets: methods, ingredients, and outcomes."

I discuss the methodology on how to tackle radiative transfer in exoplanetary atmospheres and give an overview of the crucial ingredients and common assumptions. Specifically, the focus lies on the chemistry and the opacities and how they influence the obtained temperatures and spectra of planets. A live demonstration of a radiative transfer calculation is shown using the GPU-accelerated code HELIOS.

Date:   Monday 19-Nov-2018
Speaker:   Kirill Tchernyshyov
Title:  "The spatially resolved velocity field of interstellar matter in the Milky Way and the nature of the Milky Way's spiral arms"

It is generally agreed upon that the Milky Way has spiral arms but their number and nature are still under debate. The spiral arms are thought to be either quasi-stationary density waves or transient arms that quickly form, wind up, and dissipate. These two models of spiral structure make qualitatively different predictions for the velocity fields of the gaseous spiral arms. To determine which model applies to the Milky Way, I have mapped the velocity field of interstellar gas and dust as a function of location in the Galactic plane. These maps are inconsistent with simulations of quasi-stationary density wave spiral structure and consistent with simulations of transient spiral structure.

Date:   Monday 26-Nov-2018
Speaker:   Johan Samsing
Title:  "Formation of Black Hole Mergers in Dense Stellar Systems."

I will present recent results on how binary black holes (BBHs) merge in dense stellar systems through chaotic few-body interactions. By taking into account GR effects in the equation-of-motion, I will show that dense stellar systems are likely to produce non-circular (eccentric) mergers in both LISA and LIGO with rates that are 10-100 times larger than what have been reported over the past decades using Newtonian N-body codes. In particular, I will demonstrate using simple analytical arguments that 5-10% of all BBH mergers from classical globular clusters will be eccentric in LIGO. This makes eccentricity a promising parameter for distinguishing BBH merger channels from each other. I will further discuss new ideas related to how the BBH merger distribution indirectly can be mapped using interrupted stellar tidal disruptions.

Date:   Monday 3-Dec-2018
Speaker:   Sibasish Laha
Title:  "The role of ionized and molecular outflows in quasar evolution"

The reason for cosmic down sizing of quasars is still a big puzzle in astronomy and it is commonly believed that the central active galactic nucleus (AGN) must have played a significant role in quenching itself, in a self-regulatory mechanism popularly termed “AGN feedback” . The AGN feedback also plays a crucial role in black hole and host galaxy coevolution across cosmic time. In this talk I will discuss the nature and impact of pc scale outflows from AGN, detected in X-rays, popularly known as warm absorbers (WAX sample study, Laha et al. 2014, 2016), as well as kpc scale outflows detected in IR and sub-mm, popularly known as Molecular outflows (MOX sample study, Laha et al. 2018). These different types of outflows are believed to be strong contenders for removing gas and dust from the vicinity of the super massive black hole and thereby starving it to death (quenching). However, the exact nature of the interaction of these outflows with that of the host galaxy gas and dust is still highly debated. Although we largely believe that feedback is an important mechanism by which the quenching happens, it brings us to an interesting question: Is there any fundamental difference between the central engines of the local AGN compared to their high redshift counterparts? Are they simply scaled down (lower black hole mass) versions of their higher redshift counterparts, or are different in some other way? I will present results from a sample study of low luminosity quasars (LLQSO study, Laha et al. 2018) in the local Universe to address this issue.

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