Diffuse Gamma-rays from Star Forming Galaxies

Tim PaglioneYork College, CUNY

Boston GLAST Workshop, June 21, 2007

Hunter et al. 1997

Milky Way -raysGamma-rays from Normal Galaxies A.k.a. “foreground contamination” Interactions between cosmic rays

and interstellar matter & radiationInverse Compton scatteringBremsstrahlung Neutral pion decay

“pion bump”

Gamma-rays from Starbursts Inverse Compton scattering

Enhanced (IR) photon density from numerous clusters of young massive stars

BremsstrahlungEnhanced cosmic ray density from numerous

supernova explosions

Neutral pion decayEnhanced proton density in massive molecular clouds

Blom et al. 1999

Gamma-rays from Starbursts Only upper limits from EGRET

Paglione et al. 1996; Blom, Paglione & Carramiñana 1999; Cillis, Torres & Reimer 2005)

Promise of GLAST Better sensitivity & better resolution Follows extensive surveys in IR, radio and

molecular gas emission Improved models of pion production Extends to very high energies (CANGAROO?) Probe X = N(H2)/ICO in other galaxies, cosmic ray

diffusion (radio/IR correlation), etc.