10^th Annual MKI Postdoctoral Symposium

Schedule for Wednesday May 10^th

Moderator: DJ Pasham

11:45 – 12:00  Lunch

12:00 – 12:30  Allison Noble, “Tracing Accretion Histories in z~1 Galaxy Clusters”

Understanding the influence of environment is a fundamental goal in studies of galaxy evolution, and galaxy clusters offer ideal laboratories with which to examine environmental effects on their constituent members. Clusters continually evolve and build up mass through the accumulation of galaxies, resulting in distinct galaxy populations based on their accretion history. I will discuss using cluster phase space (line-of-sight velocity versus projected clustercentric radius) as a way to probe the accretion histories of cluster galaxies to study environmental effects. I will conclude with brand new results from ALMA Cycle 3 observations of some of the first molecular gas detections in cluster galaxies at z=1.6.

12:35 – 1:05  Rozenn Boissay, “A hard X-ray view of the soft excess in AGN”

An excess of X-ray emission below 1 keV, called soft excess, is detected in a large fraction of Seyfert 1-1.5s. The origin of this feature remains debated, as several models have been suggested to explain it, including warm Comptonization and blurred ionized reflection. In order to constrain the origin of this component, we exploit the different behaviors of these models above 10 keV. Ionized reflection covers a broad energy range, from the soft X-rays to the hard X-rays, while Comptonization drops very quickly in the soft X-rays. We present here the results of a study done on 102 Seyfert 1s (Sy 1.0, 1.2, 1.5 and NLSy1) from the Swift BAT 70-Month Hard X-ray Survey catalog. The joint spectral analysis of Swift/BAT and XMM-Newton data allows a hard X-ray view of the soft excess that is present in about 80% of the objects of our sample. We discuss how the soft-excess strength is linked to the reflection at high energy, to the photon index of the primary continuum and to the Eddington ratio. In particular, we find a positive dependence of the soft excess intensity on the Eddington ratio. We compare our results to simulations of blurred ionized-reflection models and show that they are in contradiction. By stacking both XMM-Newton and Swift/BAT spectra per soft-excess strength, we see that the shape of reflection at hard X-rays stays constant when the soft excess varies, showing an absence of link between reflection and soft excess. We conclude that the ionized-reflection model as the origin of the soft excess is disadvantaged in favor of the warm Comptonization model in our sample of Seyfert 1s. 

1:10 – 1:40  Carl Rodriguez, “Dense Star Clusters as Binary Black Hole Factories”

The recent detections of gravitational waves from merging binary black holes have the potential to revolutionize our understanding of compact object astrophysics. But to fully utilize this new window into the universe, we must compare these observations to detailed models of binary black hole formation throughout cosmic time. In this talk, I will describe the dynamical evolution of a dense star cluster, and how globular clusters behave as dynamical factories for binary black holes, forging hundreds of binaries that will merge within a Hubble time.  I will also describe how the spins and eccentricity of a binary black hole are determined by its formation history, and how we can use this to discriminate between binaries formed in dynamical environments and those formed through stellar evolution in galactic fields.

2017 Postdoctoral Symposium Organizers: Rana Ezzeddine, Allison Noble, and DJ Pasham