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This Week at Physics

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Events on Thursday, January 26th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Measuring the Extragalactic Magnetic Field Via Gamma-Ray Blazar Observations
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Tom Weisgarber, University of Chicago
Abstract: Despite many efforts, the extragalactic magnetic field (EGMF), presumed to exist in the voids of the large scale structure, remains undetected. Since the EGMF may be generated either by processes in the early universe or by outflows from galaxies, and it could supply the seed fields required by many models of galactic and cluster field formation, its properties are of interest from both cosmological and astrophysical viewpoints. I will review a recently developed technique for measuring the EGMF strength using combined gamma-ray observations from the Fermi Gamma-Ray Space Telescope and ground-based instruments such as VERITAS. The technique relies on modeling the electromagnetic cascade that develops in extragalactic space due to gamma-ray interactions with the extragalactic background light and CMB and for the first time permits the placement of a lower limit on the EGMF strength. I will describe two approaches to characterizing the cascade and discuss the interpretation of gamma-ray observations of the blazar RGB J0710+591 as limits on the existence of an EGMF-induced "halo."
Host: Stefan Westerhoff
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Astronomy Colloquium
Probing the dark hearts of dusty galaxies - molecules as diagnostic tools
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Susanne Aalto, Chalmers University of Technology
Abstract: Spectacular starburst and AGN activity occurs when mergers of gas-rich systems funnel massive amounts of molecular gas and dust
into the remnant centers of ultraluminous infrared galaxies (ULIRGs). In these compact regions molecular gas rotating in the cores obscures and feeds the activity. Much of the ongoing research into initial phases of galaxy building, however, also focuses on the pre-ULIRG phases of starbursts, QSOs and assembly of galaxies via major mergers. These phases parallel conditions in lower luminosity starbursts (LIRGs) with spatially extended starburst regions. Detailed studies of LIRGS, ULIRGs, and AGN in the near-field are therefore essential both for defining the evolution of present day galaxies and sorting out key astrophysical processes in their more distant predecessors.

I will present how we can probe the nature and evolution of the dense interstellar medium (ISM), a primary evolutionary vector in starburst and AGN activity, using molecular tracers that penetrate the vast columns of dust - and also enable unique investigations of chemical and physical conditions in the molecular gas and dust. The most compact obscured nuclei, for example, need to be studied with radiatively excited molecular emission to get past the optically thick barrier.
With the emerging unprecedented capacities of ALMA we can address the nature of AGNs and starbursts, their associated molecular outflows in the context of their evolution and the starburst-AGN connection near and far.
Host: Professor John S Gallagher
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