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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-4076
DTSTART:20160212T190000Z
DTEND:20160212T200000Z
DTSTAMP:20260505T194657Z
LAST-MODIFIED:20160208T174145Z
LOCATION:4274 Chamberlin Hall
SUMMARY:High- and intermediate-velocity clouds as a tracer of cosmic r
 ays in the Galactic halo\, NPAC (Nuclear/Particle/Astro/Cosmo) Forum\,
  Luigi Tibaldo\, MPIK\, Heidelberg
DESCRIPTION:I will present the first observational estimate of the lar
 ge-scale distribution of cosmic-ray (CR) nuclei in the halo of the Mil
 ky Way\, achieved through gamma-ray observations of high- and intermed
 iate velocity clouds by the Fermi Large Area Telescope. CRs up to at l
 east PeV energies are usually described in the framework of an element
 ary scenario that involves acceleration by supernova remnants or super
 bubbles in the Milky Way disk\, and then diffusive propagation through
 out the Galaxy and its halo. The details of the propagation process ar
 e so far mainly constrained indirectly by the composition of CRs in th
 e solar system\, and then extrapolated to the whole Galaxy. The densit
 ies of CR nuclei in remote locations\, on the other hand\, can be trac
 ed via the gamma rays they produce in inelastic collisions with clouds
  of interstellar gas. Recently\, we performed a search for gamma-ray e
 mission from  several high- and intermediate-velocity clouds located i
 n the halo of the Milky Way up to ~ 7 kpc from the disk. The gamma-ray
  emission rate per hydrogen atom was found to decrease with distance f
 rom the disk\, which provides direct evidence that CRs at the relevant
  energies originate therein. Furthermore\, I will discuss how the resu
 lts call for a critical reexamination of propagation models against ot
 her direct and indirect observations of CRs.
URL:https://www.physics.wisc.edu/events/?id=4076
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